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Heterochromosomes in the Poeciliidae

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Li r r a r y
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DATE
NORTHWESTERN UNIVERSITY
HRTEROCHROMOSOMES IN THE POECILIIDAE
A DISSERTATION
SUBMITTED TO THE GRADUATE SCHOOL
IN PARTIAL FULFILMENT OF THE REQUIREMENTS
f o r t h e d eg ree
DOCTOR OF PHILOSOPHY
DEPARTMENT OF ZOOLOGY
by
JEAN CRAIG KRAFT
EVANSTON, ILLINOIS
JUNE, 1940
ProQuest Number: 10101616
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INFORMATION TO ALL USERS
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i
TABLE OF CONTENTS
Page
I n tr o d u c t i o n and S tatem en t o f P r o b le m ............................. ......................................
1
Review o f L i t e r a t u r e ......................................... . ..........................................................
3
S ex r a t i o s • • • . .................................................
3
G e n e tic a l i n v e s t i g a t i o n s and t h e o r i e s o f s e x d e te r m in a tio n . . .
5
G e n e tic a l a n a l y s is
o f A p l o c h e i l u s .......................................................
5
G e n e tic a l a n a l y s is
o f P la ty p o e c ilu s ...................................................
10
G e n e tic a l a n a l y s is o f L e b i s t e s ............................................ ...
. . .
13
G e n e tic a l a n a l y s is o f X ip h o p h o r u s ............................................................17
I n t e r s p e c i f i c c r o s s e s among th e P o e c i l i i d a e ................................... 19
C y to lo g ic a l s tu d i e s upon t e l e o s t e a n germ c e l l s ..........................................2&
M a te r ia ls and M e th o d s .............................................................................* ........................... 32
S o u rce o f m a t e r i a l ........................................................................................................ 32
P re p a ra tio n o f s lid e s
..................................................................................32
M easurem ent o f h e te ro c h ro m o s o m e s ......................................................................... 3-4
S t a t i s t i c a l a n a l y s is o f d a t a .....................................................
37
T reatm en t
o f s p e c ie s w ith two heterochrom osom es . . . . . .
T rea tm e n t
o f s p e c ie s w ith t h r e e h e te ro c h ro m o s o m e s ..................... 43
T rea tm e n t
o f s p e c ie s w ith fo u r h e te r o c h r o m o s o m e s ..................... 44
R e s u lts o f C y to lo g ic a l
37
S tu d y and S t a t i s t i c a l A n a l y s i s ...................................47
S p e c ie s w ith tw o h e te r o ch ro m o so m es.................................................................... 47
I n tr o d u c t i o n
.
............................................................................................... 47
C y to lo g ic a l o b s e rv a tio n s
S t a t i s t i c a l a n a l y s is
. . . . . . . . .
................................
49
.................................................................................
55
S p e c ie s w ith compound h e te r o c h r o m o s o m e s .......................................................64
I n tr o d u c t i o n
........................................
64
ii
S p e c ie s w ith t h r e e h e te r o ch ro m o so m es..............................................
66
C y to lo g ic a l o b s e r v a t i o n s ................................... ♦ .. ...........................
66
S t a t i s t i c a l a n a l y s i s . . . . . ...........................................................
69
S p e c ie s w ith f o u r h e te r o ch ro m o so m es...........................................................
74
C y to lo g ic a l o b s e r v a t i o n s ...................................................................* .
74
S t a t i s t i c a l a n a l y s is .................................................................................
75
Summary o f R e s u l t s ............................................................................................................
78
D is c u s s io n an d C o n c l u s i o n s ..........................................................................................
85
P o s s ib le f u n c t io n a l s ig n i f i c a n c e o f t h e heterochrom osom es . . .
85
D is c u s s io n o f t h e ty p e o f s e x -d e te rm in in g m e c h a n is m .......................
90
E v id en c e f o r t h e v ie w -p o in t t h a t s e x chromosomes i n t h e
P o e c i l i i d a e a r e i n t h e p ro c e s s o f e v o l u t i o n ...........................
96
Summary and c o n c l u s i o n s ......................................................................................
99
A c k n o w le d g m e n ts ......................................................................................................................100
B i b l i o g r a p h y ...............................................................................................................................101
F ig u re s and E x p la n a tio n o f F ig u re s
Graphs
V ita
1
I.
INTRODUCTION AND STATEMENT OF PROBLEM
D u rin g t h e p a s t f i f t e e n y e a r s , f i e l d s tu d ie s made upon t h e ovov iv ip a r o u s t e l e o s t s have drawn a t t e n t i o n t o d e v ia tio n s from t h e norm al 1 :1
s e x r a t io *
I n a d d i t i o n , r e p o r t s o f se x r e v e r s a l from th e fem ale t o t h e m ale
c o n d itio n have b een f r e q u e n t.
G e n e tic r e s e a r c h has b ro u g h t t o l i g h t two more u n u s u a l phenomena.
F i r s t , s t u d i e s o f s e x lin k a g e have shown t h e e x is te n c e o f b o th t h e Droso­
p h i l a XX-XY ty p e o f se x i n h e r i t a n c e and t h e A braxas ZZ-WZ ty p e w ith in t h e
s in g l e f a m ily , P o e c i l i i d a e .
Second, c r o s s in g o v e r betw een t h e h etero m o rp h ic
s e x chromosomes (XY o r WZ) has been d is c o v e re d f o r th e f i r s t tim e .
S in ce a b e r r a n t s e x r a t i o s and se x r e v e r s a l p o in t t o e n v iro n m e n ta l
in f lu e n c e s p la y in g a r o l e i n d e te r m in a tio n o f s e x , a n d , s in c e t h e r e s u l t s
o f g e n e tic s tu d i e s p o in t t o an i n h e r i t e d ty p e o f se x d e te r m in a tio n i n t h i s
f a m ily , s e v e r a l i n t e r e s t i n g p o s tu la tio n s c o n c e rn in g th e s e x -d e te rm in in g
mechanism i n t h i s group have been made.
W hile, a t t h i s tim e , postponem ent
o f a d is c u s s io n o f t h e s e t h e o r i e s i s a d v is a b le , th e la c k o f agreem ent b e­
tw een them i s w o rth y o f m en tio n , f o r t h i s v e r y la c k o f agreem ent i s i l l u s ­
t r a t i v e o f t h e extrem e co m p lex ity o f th e whole p roblem .
The p o s tu la tio n s
form a g rad ed s e r i e s w ith r e s p e c t t o t h e d eg ree o f em phasis p la c e d upon
e i t h e r t h e e x t r i n s i c o r i n t r i n s i c f a c t o r s in v o lv e d .
The r e s u l t s o f c y t o l o g i c a l i n v e s t i g a t i o n s o f t h i s group a ls o show
la c k o f a g reem en t.
Some c y t o l o g i s t s c la im t o have found ev id en ce o f a p a i r
o f heterochrom osom es w hich t h e y have s u g g e ste d may f u n c tio n a s se x chromo­
som es.
O th e r w o rk ers do n o t o b serv e t h e s e chromosomes and doubt t h e i r e x i s ­
te n c e .
T e le o s t chromosomes a r e s m a ll, num erous, and te n d t o be a l i k e i n
s iz e and form so t h a t i n v e s t i g a t i o n o f them i s te d io u s and d i f f i c u l t .
As a
2
r e s u l t , t h e c y t o l o g i c a l work done upon t e l e o s t s i n g e n e r a l i s r a t h e r l i m i t e d ,
and e s p e c i a l l y so when i t comes t o th e fa m ily P o e c i l i i d a e .
I n v iew o f t h e
f a c t t h a t t h e g e n e t i c a l work form s an i n t e r e s t i n g p o in t o f d e p a r tu r e , and
b eca u se t h e c y t o l o g i c a l a s p e c ts o f th e problem a r e i n d isa g re e m e n t, i t was
c o n s id e re d t h a t i t w ould be p r o f i t a b l e to make a c y t o lo g ic a l su rv e y o f t h e
gonads o f a s many P o e c iH id s a s p o s s i b l e , i n o r d e r t o a s c e r t a i n w h eth er a
p a i r o f heterochrom osom es i s p r e s e n t, an d , i f s o , w h eth er th e y c o rre sp o n d
i n m orphology and b e h a v io r t o t h e se x chromosomes w hich a r e known t o e x i s t
i n o t h e r g ro u p s o f a n im a ls .
I n a d d i tio n , an a tte m p t w i l l be made t o d i s ­
co v e r w h e th e r t h e i n d i v i d u a l chromosomes o f su ch p a i r s a r e a l i k e o r u n lik e
i n s iz e an d sh a p e .
I t w i l l a ls o be o f v a lu e t o c o r r e l a t e th e s e c y to l o g i c a l f in d in g s
w ith t h e g e n e t i c a l s tu d i e s w hich have b een made and t o re v ie w th e t h e o r i e s
o f se x d e te r m in a tio n w hich have b een p o s tu la te d f o r t h i s g ro u p , a g a in c o r­
r e l a t i n g , i n s o f a r a s p o s s i b l e , th e r e s u l t s w hich have been o b ta in e d i n t h i s
s tu d y .
The p u rp o se o f t h i s p a p e r i s f o u r - f o l d :
1.
To s tu d y e y t o l o g i c a l l y th e germ c e l l s o f tw e n ty s p e c ie s o f
P o e c i l i i d a e i n o r d e r t o d is c o v e r w h eth er h e te r o chromosomes a r e p r e s e n t i n
a l l o r some o f t h e s p e c i e s .
2.
To d e te rm in e w h e th e r th e h e te r o chromosomes, p ro v id e d th e y a r e
p r e s e n t , may be i d e n t i f i e d a s se x chromosomes,
3*
To d e te rm in e , i f p o s s ib le , w h eth er t h e heterochrom osom es a r e
m o rp h o lo g ic a lly s i m i l a r o r d i s s i m i l a r , i n o rd e r t o p o s tu l a t e an XT o r WZ con­
d i t i o n f o r e a c h s p e c ie s .
4.
To c o r r e l a t e c y t o l o g ic a l o b s e rv a tio n s w ith g e n e t i c a l r e s e a r c h
3
and w ith t h e t h e o r i e s o f s e x d e te r m in a tio n w hich have been advanced f o r t h i s
group o f t e l e o s t s .
II.
REVIEW OF LITERATURE
A re v ie w o f r e le v a n t l i t e r a t u r e may be o rg a n iz e d aro u n d t h r e e
t o p i c s , nam ely, s tu d i e s upon s e x r a t i o s , s t u d i e s upon i n h e r it a n c e and s e x
d e te r m in a tio n , and c y t o l o g i c a l s tu d i e s o f t h e g e m c e l l s .
Sex R a tio s
The norm al s e x r a t i o i n most d io e c io u s an im a ls i s 1 :1 b u t t h e r e
i s e v id e n c e o f a d e v ia tio n i n f a v o r o f one s e x o r a n o th e r i n some o f th e
o v o v iv ip a ro u s t e l e o s t s .
H ild e b ra n d (1927) w r ite s t h a t im m ature Gambusia
a f f i n i s show a r a t i o o f 1 :1 b u t t h a t among a d u lt f i s h th e r a t i o a p p e a rs t o
be 1 :2 .5 m ale t o fe m a le .
S. W. G e is e r (1924 and 1 9 2 5 ), w orking upon th e
same s p e c i e s , r e p o r t s a s i m i l a r r a t i o .
B arney and Anson (1921) a ls o f in d
t h a t i n f i e l d c o l l e c t i o n s o f Gambusia a f f i n i s , made a t a l l tim e s o f th e
y e a r , t h e r e a r e alw ays more fem ales th a n m a le s.
E sse n b e rg (1923) r e p o r t s
t h a t i n XLphophorus h e l l e r i i t h e sex r a t i o a t b i r t h i s 1 :2 m ale t o fem ale
and t h a t a t m a tu r ity i t i s r e v e r s e d t o 2 :1 m ale t o fe m a le .
He e x p la in s
t h i s u n u s u a l r a t i o by a r e v e r s a l o f o n e - h a lf o f th e fem ales t o m a le s.
A
p rep o n d e ra n c e o f m ales o v e r fe m ales i n a d u lt X iphophorus i s d i r e c t l y op­
posed t o t h e o b serv ed r a t i o i n a d u lt Gambusia a f f i n i s , a f a i r l y c l o s e ly r e ­
la te d f is h .
M. Gordon (1937) p o in ts out t h a t i n 1930 he and Dr. C. L. Hubbs
found two s i z e s o f m ale X iphophorus i n a s m a ll la k e n e a r J a la p a , V era C ruz,
M exico.
W hile t h e sword was w e ll d eveloped i n b o th g ro u p s, t h e l a r g e r m ales
showed d e g e n e ra te gonopods, w ith gonads w hich v/ere e i t h e r v e r y sm a ll o r com­
p l e t e l y l a c k in g .
The s m a lle r m a le s, how ever, c o n ta in e d w e ll d e v e lo p e d , n o r­
4
m al t e s t e s .
S in c e t h e o n ly o th e r s p e c ie s i n t h e l a k e , P seudoxiphophorus
b lm m acu latu s. i s n o t c l o s e ly r e l a t e d t o X iphophorus, t h e o c c u rre n c e o f t h e
la r g e form s was a t t r i b u t e d t o tr a n s f o r m a tio n o f s e x from fem ale t o m ale
r a t h e r th a n t o h y b r id i z a ti o n .
Thus th e s e f i e l d o b s e rv a tio n s te n d t o le n d
su p p o rt t o E s s e n b e rg ts c o n te n tio n .
B r e id e r (1935)* w orking w ith X iphophorus
h e l l e r i i » s t a t e s t h a t t h e s e x r a t i o may show e i t h e r a p rep o n d eran c e o f f e ­
m ales o r o f m a le s .
He b e lie v e s t h e c o n t r o ll i n g f a c t o r s t o be h e r e d ita r y
b ecau se e x p e rim e n ta l a n a ly s e s o f su ch f a c t o r s a s s e a s o n a l d i f f e r e n c e s , age
o f sperm , te m p e r a tu r e , u n fa v o ra b le fo o d , sp ace l i m i t a t i o n , age o f p a r e n ts
and s iz e o f b ro o d showed no in f lu e n c e upon t h e s e x r a t i o .
However, a c c o rd ­
in g t o t h e r e s u l t s o f B ellam y (1924)> e x c e ss m ales a r e c h a r a c t e r i s t i c .
Out
o f 2835 young b o rn , w ith a m o r t a l i t y o f 2 6 .9 p e r c e n t, 1126 were m ales and
947 fe m a le s .
B o u len g er (1912) shows a r a t i o o f t h r e e fem ales t o one m ale
i n G ira rd in u s p o e c ilo id e s and c la im s i n l e t t e r s t o H uxley (1920) t h a t th e
r a t i o changed d u r in g t h e w in te r t o about two fem a le s t o t h r e e m a le s.
T h is
p e r io d l a s t e d s i x weeks and was su cceeded by a t h i r d p e r io d c h a r a c te r iz e d
by a 1 :1 r a t i o .
The norm al 1 :1 r a t i o p e r s i s t e d f o r th e re m a in d e r o f th e
tim e th e y w ere b r e d , a p e r io d o f s e v e r a l y e a r s .
Huxley e x p la in s t h e p e r io d
o f v a r i a b i l i t y by assum ing a n XX-XY ty p e o f s e x mechanism i n w hich a d e f i n i t e
p e rc e n ta g e o f XI m ales r e v e r s e d a s th e r e s u l t o f an u p s e t i n t h e norm al com­
p le x o f e n v iro n m e n ta l f a c t o r s .
A cco rd in g t o him, c o n tin u a tio n o f th e modi­
f y in g in f lu e n c e a t t h e same l e v e l o f i n t e n s i t y w i l l produce two e f f e c t s :
( l ) t h e p r o p o r tio n o f so m atic fem ales (XY) w i l l in c r e a s e and t h e p re p o n d e r­
ance o f g e n o ty p ic fem ales d e c re a s e ; ( 2 ) t h i s r e s u l t s i n a g r e a t e r prep o n ­
d e ra n c e o f m ales i n t h e g e n e r a tio n a f t e r th e end o f t h e f i r s t p e r io d , when
t h e m o d ify in g i n f lu e n c e s c ea se t o o p e r a te .
Henn (1916) found t h a t i n L e b is -
5
t e s r e t i c u l a t u s . c o l l e c t e d i n t h e f i e l d and c l o s e ly r e l a t e d t o X iphophorus,
/
t h e r a t i o was 1 : 1 *
W hatever t h e cau se o f a t y p i c a l s e x r a t i o s i n t h e s e f i s h may b e ,
th e f a c t t h a t t h e y o c c u r i s c e r t a i n l y i n d i c a t i v e o f an u n s ta b le s e x d e t e r ­
m in in g m echanism .
W hile i t i s im p ro b ab le t h a t any c y t o lo g ic a l s tu d y o f
th e germ c e l l s o f t h i s group w i l l r e v e a l any u n d e r ly in g " c a u s e ” f o r t h e s e
abnorm al r a t i o s , i t w i l l p ro v e o f v a lu e t o know w h eth er o r n o t t h e p o e c il i i d s p o s s e s s i d e n t i f i a b l e se x chromosomes, and t o d is c o v e r w h eth er su ch
chromosomes d i f f e r m ark ed ly i n t h e i r m orphology and b e h a v io r , from t h e
autosom es*
G e n e tic a l I n v e s t i g a t i o n s and T h e o rie s o f
Sex P e t e rm in a tio n
G e n e tic a l s tu d i e s made upon t e l e o s t s o f th e o r d e r C y p rin o d o n tes
have been c o n fin e d t o one o v ip a ro u s form , A p lo c h e ilu s o r O ry z ia s l a t i p e s o f
t h e f a m ily C y p rin o d o n tid a e , and t o s p e c ie s o f f o u r g e n e ra o f t h e fa m ily
P o e c iliid a e :
A.
P l a t y p o e c i l u s , L e b is t e s , X iphophorous and L im ia.
G e n e tic a l a n a l y s i s o f A p lo c h e ilu s
A ida (1921) has d is c o v e re d th r e e genes f o r c o lo r p a t t e r n s i n
A p lo c h e ilu s and one o f t h e genes shows sex lin k a g e .
R i s a s e x - lin k e d
gene p ro d u c in g t h e x a n th o p h o re s r e s p o n s ib le f o r y e llo w c o lo r a t io n .
B is
an au to so m al gene p ro d u c in g m elanophores w hich a r e u n ifo rm ly d i s t r i b u t e d
th ro u g h o u t t h e body.
B1 i s an au to so m al gene p ro d u c in g m elanophores w hich
o n ly p a r t i a l l y c o v e r t h e body.
The w ild ty p e A p lo c h e ilu s i s brown, a c o lo r
pro d u ced by t h e o c c u rre n c e o f genes B and R t o g e t h e r .
Gene B a lo n e g iv e s
b lu e c o l o r a t io n and gene R a lo n e an o ra n g e -re d w hich A ida speaks o f sim p ly
6
as re d ,
B1 w henever p r e s e n t w ith o u t gene B, p ro d u ces a v a r i e g a te d e f f e c t ,
b u t when com bined w ith B i s r e c e s s i v e .
w h ite i n d i v i d u a l s .
Absence o f genes B and R r e s u l t i n
A p p ro p ria te c r o s s e s in d i c a t e d t h a t s e x i n h e r it a n c e i n
A p lo c h e ilu s b e lo n g s t o t h e XX-XY D ro so p h ila t y p e .
c e s s iv e w h ite fem ale w ith a homozygous re d m ale.
A ida c ro s s e d a p u re r e ­
The
g e n e r a tio n was
a l l h e te ro z y g o u s r e d and when b a c k -c ro s s e d t o t h e w h ite r e c e s s iv e fem ale
gave a n F£ o f w h ite fe m a le s and re d m a le s.
I f t h e A braxas ty p e o f s e x de­
te r m i n a t i o n i s assum ed, t h e e x p e c te d F2 r e s u l t would be w h ite fem ales and
m ales i n e q u a l num bers.
However, t h e a fo re m e n tio n e d r e s u l t s n e c e s s i t a t e
t h e a ssu m p tio n o f an XX-XY ty p e o f d e te r m in a tio n .
o b ta in e d a c r o s s - o v e r o f R from X t o Y.
I n a l a t e r c r o s s , he a ls o
The e x p e c ta tio n from t h e c r o s s o f
a h e te ro z y g o u s r e d fem ale w ith a h e te ro z y g o u s r e d m a le , was re d fe m a le s,
re d m ales and w h ite m a le s .
He a c t u a l l y o b ta in e d two w h ite fem ales whose
p re s e n c e c o u ld e a s i l y be e x p la in e d by t h e assu m p tio n o f a c r o s s - o v e r o f R
from X t o Y.
A ida (1930) i n f u r t h e r s tu d i e s on A p lo c h e ilu s claim ed t h a t
o f h is supposed c r o s s - o v e r s were a c t u a l l y c a s e s o f n o n - d is ju n c tio n .
some
In
m a tin g re d m ales (XyY^) t o w h ite fem a le s (Xr Xr ) he o b ta in e d a c r o s s - o v e r
o f R from Y t o X i n t h e r a t i o o f 1 :3 0 0 .
I n e x p erim en ts o f s i x y e a r s d u ra ­
t i o n he o b ta in e d 2023 norm al and 28 e x c e p tio n a l o f f s p r i n g .
D uring t h e
m a tin g o f r e d m ales (X^Yr ) t o w h ite fem ales (XpXj,) he o b ta in e d c r o s s - o v e r
o f t h e R gene i n t h e r a t i o 1 :360 f o r t h e r e were 500 norm al o f f s p r i n g t o IX
e x c e p tio n a l.
However, su b seq u en t b re e d in g o f th e e x c e p tio n a l re d m ales t o
r e c e s s i v e fe m a le s showed tw o t o be t r u e c r o s s - o v e r s , and seven t o have r e ­
s u l t e d from n o n - d is ju n c tio n o f Xg iv in g phen o ty p es o f t h e fo rm u la X^X^Y^,.
I f th e
n o n - d is j u n c t i o n a l m ales had been t h e r e s u l t o f c r o s s - o v e r and
co n -
7
s e q u e n tly o f t h e fo rm u la ^ Y ^ , t h e i r o f f s p r i n g when b a c k -c ro s s e d t o a r e ­
c e s s iv e fem ale sh o u ld have been r e d m ales and w h ite fem ales i n e q u a l num­
b ers,
However, s in c e t h e y w ere XjjXpY , th e y p ro d u c e d , when c ro s s e d t o th e
r e c e s s i v e fe m a le s , 996 r e d fe m a le s , 953 w h ite fe m a le s , 11 r e d m a le s, and
8 w h ite m a le s.
F u r th e r b re e d in g c o n tin u e d t o g iv e a m a jo r ity o f fe m a le s ,
w ith how ever, a n i n c r e a s e i n t h e p r o p o r tio n o f s o n s .
A ida was u n a b le t o
t e s t t h e e x c e p tio n a l w h ite fem ales i n o r d e r t o a s c e r t a i n w h eth er th e y were
t h e p ro d u c t o f c r o s s - o v e r (XpX^,) o r o f n o n - d is ju n c tio n (Xr 0 ) .
W ith o n ly
2 o f t h e 14- e x c e p tio n a l form s p ro v in g th e m se lv e s t o be t r u e c r o s s - o v e r s ,
t h e r a t i o o f c r o s s - o v e r o f genes from X t o Y becomes 1:1200 in s t e a d o f
1 :3 6 0 .
T h e re f o re , t h e R gene c r o s s e s o v e r from Y t o X ab o u t f o u r tim e s
o f t e n e r th a n from X t o Y.
T hus, a s A ida p o in ts o u t, i f t h e Y chromosome
lo s e s a dom inant gene more e a s i l y th a n i t g a in s one, i n o th e r a n im a ls a s
w e ll a s i n A p lo c h e ilu s , t h i s may be wa p l a u s i b l e e x p la n a tio n o f t h e s o c a l l e d empty Y chromosome o f D ro s o p h ila 1*. (page 4 )
Winge (1930) s u g g e ste d t h a t A ida was d e a lin g w ith XX m ales r a t h e r
th a n w ith n o n - d is j u n c t i o n a l fo rm s.
By assum ing s e x r e v e r s a l , a l l t h e o f f ­
s p r i n g sh o u ld be fem ale when a n XX m ale i s c ro s s e d w ith a norm al XX fe m a le .
However, s in c e A ida o b ta in e d a few m ales th e f i r s t g e n e r a tio n , and an i n ­
c r e a s in g p r o p o r tio n o f m ales i n t h e su c c e e d in g g e n e r a tio n s , Winge assum ed
t h a t a s a r e s u l t o f in b r e e d in g , genes w ith a m a le -p ro d u c in g te n d e n c y w ere
b e in g s e l e c t e d and accu m u lated upon t h e autosom es.
A ida (1936) shows t h a t
b r e e d in g t e s t s have p ro v en h is e x c e p tio n a l m ales n o t t o be th e p ro d u c t o f
n o n - d is ju n c tio n and a d o p ts Winge* s assu m p tio n t h a t he i s w orking w ith soma­
t i c m ales w ith an XX g en o ty p e.
He r e j e c t s , however, th e s u g g e s tio n t h a t
t h e i n c r e a s i n g p r o p o r tio n o f m ales i n h is XX m ale s to c k s r e s u l t s from an
a c c u m u la tio n , upon t h e autosom .es, o f genes w ith m a le -d e te rm in in g te n d e n c ie s ,
and f o rm u la te s what he te rm s ” a new th e o r y o f s e x d e te r m in a tio n ." He b e­
l i e v e s t h a t genes f o r p rim a ry se x c h a r a c te r s a r e lo c a te d i n th e autosom es,
b u t n eed t o be a c t i v a t e d by t h e s o - c a l l e d " s ti m u l a tin g genes" i n th e se x
chromosomes.
genes p r e s e n t .
Sex d i f f e r e n t i a t i o n i s a r e s u l t o f t h e number o f s tim u la tin g
When t h e y a r e p r e s e n t i n a q u a n tity above a c e r t a i n th r e s h o l d
v a lu e , a u to so m al fe m in in e genes a r e s tim u la te d .
t h r e s h o l d a c t i v a t e m a sc u lin e g e n e s.
Q u a n titie s below t h i s
I n h e te ro g a m e tic m ales th e t o t a l sum
o f s ti m u l a t o r s i n X and Y i s l e s s th a n t h a t c o n ta in e d i n two X chromosomes.
I n h e te ro g a m e tic fe m a le s j u s t t h e r e v e r s e c o n d itio n i s t r u e .
He assum es
t h a t t h e p o te n c ie s i n X and Y a r e s t a b l e i n th e w ild brown t y p e .
In th e
c o lo r e d v a r i e t i e s p ro d u ced by i n t e n s i v e in b re e d in g th e p o te n c ie s o f th e
s t i m u l a t i n g genes f l u c t u a t e .
As a r e s u l t , a few XX co m b in atio n s become low
i n p o te n c y and f a l l below th e t h r e s h o ld v a lu e , p ro d u c in g som atic XX m a le s.
G oldschm idt (1937) m a in ta in s t h a t A id a’ s "new" th e o r y i s e s s e n ­
t i a l l y t h e th e o r y t h a t h e, G o ld sch m id t, fo rm u la te d i n o r d e r t o e x p la in se x
d e te r m in a tio n i n t h e Gypsy moth L y m a n tria .
A ccording t o G oldschm idt what
A ida te rm s " s t i m u l a t i n g genes" i n t h e X chromosome a r e i d e n t i c a l w ith th e
M g en es i n t h e Z chromosome o f L y m an tria.
A id a ’ s id e a o f d i f f e r e n t i a l quan­
t i t i e s o f s ti m u l a t i n g genes w orking upon t h e p rim a ry se x genes i n t h e a u to ­
somes i s i n r e a l i t y a r e s ta te m e n t o f G o ld sch m id t’ s id e a t h a t d i f f e r e n t quan­
t i t i e s o f M a r e b a la n c e d a g a in s t a q u a n t ity o f F upon t h e autosom es.
A id a 's
" th r e s h o l d v a lu e " i s com parable t o G o ld sc h m id t's " E p i s t a t i c minimum f o r th e
b a la n c e F/M” , w h ile t h e id e a o f f l u c t u a t i n g q u a n t i t i e s o f th e s ti m u l a t o r i s
e q u iv a le n t t o t h e c o n cep t o f a weak and s tr o n g M.
W itsc h i (1932) r e i n t e r p r e t s A id a 's r e s u l t s i n t h e l i g h t o f h is own
t h e o r y w hich was d e v is e d t o e x p la in c o n d itio n s found i n th e s o - c a l l e d d i f ­
f e r e n t i a t e d and - u n d if f e r e n tia te d r a c e s o f f r o g s .
He, l i k e G oldschm idt,
assum es t h a t fe m a le -d e te rm in in g genes F and f a r e lo c a te d i n X and Y, w hereas
m a le -d e te rm in in g f a c t o r s M a r e borne i n t h e autosom e g ro u p .
Q u a n tita tiv e
v a lu e s a r e a r b i t r a r i l y a s s ig n e d t o th e s e f a c t o r s , w ith th e r e s u l t t h a t th e
norm al A p lo c h e ilu s fem ale i s d e s ig n a te d a s M-15 M-15 F+17 F+17 ( t o t a l +4 )
and t h e m ale a s M-15 M-15 F+17 f+9 ( t o t a l - 4 ) •
The F f a c t o r s on X, l i k e
so m atic f a c t o r s , a r e assum ed t o be l i n e a r l y a rra n g e d , and w h ile th e sum
t o t a l o f t h e i r p o te n c ie s rem ain s 17* i n d i v i d u a l f a c t o r s v a r y i n p o te n c y .
The above c o n d itio n s a l s o h o ld f o r t h e f f a c t o r s upon Y, w ith t h e e x c e p tio n
t h a t t h e sum o f t h e i r t o t a l p o te n c ie s i s 9 i n s t e a d o f 1 7 A id a ’ s e x c e p tio n a l r e d m ales (X^Jf^) a r e assumed t o have o r ig in a te d
from a c r o s s - o v e r o f gene R from X t o Y, accom panied by c r o s s - o v e r s o f sex
genes a s w e l l .
I n c a s e s w here s e x f a c t o r s o f low i n d iv i d u a l p o te n c y happen
t o c r o s s - o v e r from X t o Y, t h e sum o f t h e p o te n c ie s o f t h e f a c t o r s i n X
changes from +17 t o a lo w e r num ber.
I f a gam ete c o n ta in in g an X chromosome
w ith F f a c t o r s o f a b n o rm a lly low p o te n c y i s f e r t i l i z e d by a sperm atozoan
c o n ta in in g an X o f low v a lu e , t h e combined e f f e c t o f t h e two XXs may n o t be
f a r enough on t h e p o s i t i v e s id e o f t h e s c a le t o overcome t h e n e g a tiv e t e n ­
dency o f t h e au to so m es.
Thus XX so m atic m ales make t h e i r a p p e a ra n c e .
As
j u s t i f i c a t i o n f o r t h e a p p l i c a t i o n o f c o n c lu s io n s g a in e d from t h e stu d y o f
am phibia t o f i s h , Wit sc h i c i t e s th e p e r io d o f ju v e n ile h erm ap h ro d itism com­
mon t o b o th g ro u p s.
Among t h e C y p rin o d o n tes E ssen b erg (1923, 1926) and
D ild in e (1936) have g iv e n e v id e n c e o f su ch a c o n d itio n i n Xyphophorous and
L e b is t e s , r e s p e c t i v e l y .
B.
G e n e tic a l A n a ly s is o f P la t.y p o e c ilu s
B ellam y (1923, 1928) found e v id en ce t h a t fo u r ty p e s o f c o l o r a tio n
i n P l a ty p o e c ilu s m a c u la tu s a r e i n h e r i t e d a s s e x - lin k e d m u ltip le a l l e l o ­
m orphs, w ith t h e fem ale t h e h e te ro g a m e tic se x ; n ig r a (N ), p u lc h r a ( P ),
ru b ra (R ) and w h ite (W) c o n s t i t u t e t h e m u ltip le a lle lo m o rp h ic s e x lin k e d
s e rie s .
Hence p u lc h r a , n ig r a and r u b ra a r e c o n s id e re d t o be gene m u ta tio n s
a t a s i n g l e lo c u s on one o f t h e s e x chromosomes.
B ellam y (1933b) d is c u s s e s t h e p h e n o ty p ic a s p e c ts o f th e m u ltip le
a lle lo m o rp h ic c h a r a c t e r s .
N ig ra form s a r e s t i p p l e d i n ap p earan ce due t o
arran g em en t o f m acrom elanophores i n a d e f i n i t e p a t t e r n .
Rubra i s r e d ,
s t i p p l e d and s p o tte d i n a p p e a ra n c e and p u lc h ra i s s t i p p l e d , s p o tte d and
n o n -re d .
p o e c ilu s .
W hite i s r e s p o n s ib le f o r t h e o liv a c e o u s -g r e y w ild ty p e o f P la ty ­
M ales (ZZ) may be h ete ro z y g o u s f o r any tw o f a c t o r s w h ile fem ales
(ZW) may c a r r y o n ly o n e.
Red c o lo r and b la c k s p o ts , w hich make up th e
p h e n o ty p ic a s p e c t o f r u b r a , were n e v e r s e p a r a te d .
n e v e r o b ta in e d r e d , n o n - s p o tte d i n d i v i d u a l s .
I n o th e r w ords, Bellam y
However, he does b e lie v e t h a t
t h e f a c t o r s f o r r e d and s p o ts had s e p a r a te o r ig i n s and a s a consequence o f
c r o s s - o v e r betw een s e x chromosomes, became lin k e d t o g e t h e r t o form t h e ru b ra
com plex.
B ellam y (1933a) d e s c r ib e s an au to so m al c h a r a c te r , g o ld , i n P la t y ­
p o e c ilu s .
I t b eh av es a s a sim p le M endelian c h a r a c te r , r e c e s s iv e t o th e w ild
ty p e .
P la ty p o e c ilu s m a c u la tu s has a l s o been worked upon i n t e n s i v e l y by
Myron G ordon.
Gordon (1 9 2 6 a, 1927* 1931) s tu d ie d th e h is to lo g y o f t h e c o lo r
p a t t e r n s and d is c o v e re d t h a t th e y a l l may be t r a c e d back t o changes i n th e
arran g em en t o f f o u r b a s ic ty p e s o f ch ro m ato p h o res, nam ely m icro m elan o p h o res,
n
m acro m elan o p h o res, x a n th o p h o re s and e r y t h ro p h o res .
The s t i p p l e d p l a t y ( S t ) , w hich B ellam y te rm s w h ite (W), i s a d ark
o l i v e —b u f f due t o d o t—li k e m icro m elanophores o c c u r rin g i n la r g e numbers o v er
t h e body and o v e r ly in g t h e x a n th o p h o re s .
B oth se x e s show th e p a t t e r n b u t
t h e m ales a r e b r i g h t e r .
The s p o tte d v a r i e t y (Sp) (Bellamy* s p u lc h r a (P )) has a ground c o lo r
l i k e t h e s t i p p l e d p l a t y , due t o t h e a c ti o n o f x a n th o p h o re s and m icrom elanop h o r e s , an d , i n a d d i t i o n , p o s s e s s e s m acrom elanophores w hich produce la r g e
b la c k , i r r e g u l a r l y d i s t r i b u t e d pigm ent s p o ts .
The b la c k v a r i e t y ( n ig r a ) (N) i s c o n s id e re d t o be an extrem e phase
o f t h e b la c k s p o tte d v a r i e t y .
A la r g e s h e e t - l i k e b la c k band o f macrom elano­
p h o re s e x te n d s from t h e r e g io n b e h in d th e eye t o t h e b ase o f t h e c a u d a l f i n .
M icrom elanophores and x an th o p h o re s a r e a l s o p r e s e n t .
The r e d v a r i e t y (R - Sp o r R a lo n e ) i d e n t i c a l w ith th e r u b ra (R)
v a r i e t y o f B ellam y, may c o n ta in a l l f o u r ty p e s o f ch ro m ato p h o res.
However,
th e m icro m elan o p h o res p ro d u c in g s t i p p l i n g and th e m acrom elanophores p ro ­
d u c in g s p o tt i n g may be a b s e n t, r e s u l t i n g o f c o u rse i n a p u re r e d t y p e .
T h is
i s c o n tr a r y t o Bellamy* s r e s u l t s , f o r he n e v e r o b ta in e d a s e p a r a tio n o f re d
from s p o ts .
The g o ld v a r i e t y c o n ta in s o n ly x an th o p h o res and i s p u re g o ld i n
c o lo r.
I t i s th u s e v id e n t t h a t t h e r e a r e th r e e f a c t o r s w hich may be t e s t e d
g e n e t i c a l l y , t h e i n h e r i t a n c e o f e r y t h ro p h o re s, m icrom elanophores and macro­
m e lan o p h o re s.
C ro sses were made by Gordon (1927) w ith r e d , g o ld and s t i p p l e d
s tra in s .
C ro s sin g o f a h etero zy g o u s s p o tte d , s t i p p l e d fem ale (Z g^W -Stst) t o
t o a h e te ro z y g o u s s p o tt e d , s t i p p l e d m ale ( ^ p Z g p - S t s t ) gave f o u r pheno­
t y p e s , i n d i c a t i n g t h a t tw o p a i r s o f f a c t o r s a r e o p e r a tin g .
I n a d d iti o n t o
t h e p a r e n t a l p h en o ty p e ( s p o t t e d , s t i p p l e d ) and th e p u re r e c e s s iv e pheno­
ty p e o f t h e fem ale g r a n d p a re n t, n o n - s p o tte d , n o n - s tip p le d , two new c l a s s e s —
n o n - s p o tte d , s t i p p l e d , and n o n - s tip p le d , s p o tte d —made t h e i r a p p e a ra n c e .
E x am in atio n o f se x e s i n t h e a fo re m e n tio n e d c r o s s showed m ales and
fe m a le s t o be p r e s e n t i n a l l c l a s s e s e x cep t th e p u re r e c e s s iv e c l a s s , nons p o tte d : n o n - s tip p le d , and t h e n o n - s p o t te d :s ti p p le d c l a s s .
two c o n ta in e d o n ly fe m a le s .
These l a t t e r
T hus, w h ile th e f a c t o r f o r s t i p p l i n g i s a u to ­
som al, t h a t f o r s p o t t i n g i s se x lin k e d .
S ubsequent c r o s s e s have
th u s
shown t h a t n ig r a and r e d a r e sex lin k e d ,
c o n firm in g Bellamy* s e a r l i e r work i n 1922 and 1928.
F u r th e r t e s t i n g o f t h i s
ty p e by means o f d i r e c t , r e c i p r o c a l and
b a c k - c ro s s e s has s u b s t a n t i a t e d t h e h y p o th e s is t h a t t h e Abraxas ty p e o f sex
d e te r m in a tio n o p e r a te s i n P la ty p o e c ilu s m a c u la tu s .
When p u re s t i p p l e d w ith o u t t h e c o m p lic a tin g f a c t o r o f s e x lin k e d
s p o ts , was t e s t e d w ith t h e p u re au to so m al g o ld r e c e s s i v e , t h e s t i p p l e d F-^
g e n e r a tio n showed th e f a c t o r f o r s t i p p l e t o be dom inant.
F r a s e r and Gordon (1928, 1929) do n o t b e l i e v e , a s does B ellam y,
t h a t r e d and s p o ts a r e members o f t h e same a lle lo m o rp h ic s e r i e s , f o r a
norm al re d s p o tte d fe m a le w i l l tr a n s m it b o th c h a r a c te r s t o h e r s o n s.
C ro sses
betw een r e d - s p o t t e d f i s h and t h e r e c e s s iv e gold show b re a k s i n th e lin k a g e
betw een r e d and s p o ts b eca u se o f c r o s s - o v e r betw een t h e W and Z chromosomes.
I n one i n s t a n c e , F r a s e r and Gordon o b ta in e d a c r o s s - o v e r o f b o th R and Sp
from t h e Z chromosome t o t h e W, p ro d u c in g a Zr s p Wttbp
DC fem ale.
When t h i s e x -
c e p t i o n a l fem ale was c ro s s e d t o a m ale, h ete ro z y g o u s f o r b o th re d and s p o ts ,
rsp '
tw o t y p e s o f fem ale s were o b ta in e d , ZDO
and Z
W_ 0 .
7 RSp RSp
r s p RSp
The
f i r s t i n d i v i d u a l i s v e r y u n u s u a l, f o r i t r e p r e s e n t s a c o n d itio n o f homo­
z y g o s ity i n t h e h e te ro g a m e tic se x .
C.
G e n e tic a l A n aly ses o f L e b is te s
I n L e b is te s r e t i c u l a t u s , Winge (1922a and b ) , has d is c o v e re d a
c o n d itio n o f o n e -s id e d m a sc u lin e i n h e r it a n c e , w hich has le d him t o conclude
t h a t an XX-WY ty p e o f s e x mechanism i s o p e r a tin g .
B oth t h e X and X chromo­
somes b e a r c o lo r f a c t o r s b u t , b ecau se o f extrem e s e x u a l dim orphism , c o lo r genes
c a r r i e d by fem a les n e v e r become p h e n o ty p ic a lly e x p re s s e d .
I n L e b is t e s , a s w e ll a s i n A p lo c h e ilu s and P la ty p o e c ilu s , t h e r e
i s e v id e n c e o f c r o s s - o v e r betw een t h e h etero m o rp h ic se x chromosomes, w hich
i n t h e c a se o f L e b is te s ta k e s p la c e betw een th e X and Y.
Winge (1923)
d e s c r ib e s a f a c t o r e lo n g a tu s ( e ) w hich i s l o c a te d i n th e X.
E lo n g a tu s i s
r e s p o n s ib le f o r a p r o lo n g a tio n o f t h e d o r s a l edge o f th e c a u d a l f i n and
f o r v i v i d r e d d is h - y e llo w c o lo r in g on i t s d o r s a l and v e n t r a l m a rg in s .
An
^e^rna mal e was E ^ te d t o a fem ale w ith o u t c o lo r f a c t o r s i n th e X, (XQX0 ) .
A ll fe m a le s were e x p e c te d t o c a r r y t h e e lo n g a tu s f a c t o r and none o f t h e
103,168 t o p o s s e s s i t .
^e1* f a c t o r .
However, one male out o f s e v e n ty - th r e e showed th e
F u r th e r t e s t s i n d i c a te d t h a t " e *1 had c ro s s e d o v er from X t o
Y and t h a t t h e e x c e p tio n a l m ale had th e form ula X0YpTna.
Winge (1927) l o c a t e s e ig h te e n genes w hich a r e a s s o c ia te d w ith
t h e d e te r m in a tio n o f c o lo r p a t t e r n i n L e b is te s .
one i s a u to so m a l.
Of t h e e ig h te e n g e n e s, o n ly
Mine o f th e re m a in in g s e v e n te e n a r e i n v a r ia b ly lo c a te d
on Y and show o n e -s id e d m a sc u lin e i n h e r it a n c e .
T hree o f th e genes a r e con­
s i s t e n t l y l o c a te d i n X and f i v e o f them c ro s s o v er i n v a r io u s w ays, from
X t o I , I t o X o r from X t o X.
T e s t c r o s s e s show t h a t w henever th e s e genes
a r e p r e s e n t i n t h e m ale genotype th e y become e x p re s s e d p h e n o ty p ic a l l y .
Hence t h e s e genes have no r e c e s s i v e a lle lo m o rp h s .
Demerec (1928) s t a t e s
t h a t t h e ch an ces o f s e v e n te e n o u t o f e ig h te e n dom inant m u ta tio n s b e in g l o ­
c a te d on one o u t o f tw e n ty - th r e e p a i r s o f chromosomes a r e one i n e ig h t tim e s
21
10 ^ The f i g u r e i s to o low t o be p r o b a b le .
Even w ith t h e assu m p tio n t h a t
t h e m u t a b i l i t y o f t h e heterochrom osom es i s h ig h e r th a n t h a t o f t h e a u to ­
som es, t h e s e x chromosomes would have t o be 374 tim e s a s m utable a s th e
au to so m es.
T h is , t o o , i s re g a rd e d by Demerec a s im p ro b a b le .
Demerec would
assum e t h a t chromosomes o f L e b is te s do not s e g re g a te in d e p e n d e n tly , b u t,
i n s t e a d , c e r t a i n ones form a chromosome com plex, w hich behaves a s a u n i t
d u r in g t h e r e d u c tio n d i v i s i o n .
a p p e a r t o be s e x - l i n k e d .
Thus th e s e s e v e n te e n c h a r a c te r s would m erely
W ingeTs c a s e s of c r o s s - o v e r would th e n r e s u l t from
re c o m b in a tio n s o f t h e chromosomes m aking up th e more o r l e s s s ta b l e chromo­
some com plex.
Winge (1934a) does n o t a c c e p t t h e above e x p la n a tio n .
He claim s
t h a t s in c e c r o s s - o v e r s o c c u r, i n o rd e r t o ad o p t Demerec*s s u g g e s tio n one
w ould have t o assum e a new m echanism, by means o f w hich nth e v a r io u s chromo­
some p a i r s 7<rere u n e q u a lly o f te n s e t f r e e from t h e n o rm a lly o c c u r rin g chromo­
some a s s o c i a t i o n .
T h is a ssu m p tio n would mean a f a t a l blow t o a l l c y to g e n e tic s
and e s p e c i a l l y t o t h e a p p re h e n sio n o f c r o s s - o v e r .M (page J+8)
F u rth e rm o re ,
i n s p i t e o f t h e low c r o s s - o v e r v a lu e s , WTin g e has been a b le t o s u c c e s s f u ll y
map o u t t h e X and Y chromosomes w ith r e s p e c t t o t h e exam ined g en es.
Winge (1930) o b ta in e d m ales i n h is s to c k s w hich were i n t e r p r e t e d
t o be gerrtypacally XX.
W hile u s u a lly t h e fem ale L e b is te s do not show c o lo r
c h a r a c t e r s , o c c a s io n a lly fe m ales dev elo p c o lo r , gonopods and se x g la n d s con-
j t a i n i n g b o th o v a r ia n and t e s t i c u l a r t i s s u e .
M a le -lik e fe m a le s, w hich showed t r a c e s o f th e c o lo r p a t t e r n s f o r
w hich t h e y w ere g e n o ty p ic a lly homozygous, were m ated t o m ales o f th e same
J
race.
T hese m ales c a r r i e d t h e m a c u la tu s f a c t o r upon t h e i r Y chromosomes.
; The Ma gene i n t h e geno ty p e o f a m ale L e b is te s I s d e te c te d p h e n o ty p ic a lly
by t h e p re s e n c e o f a l a r g e b la c k sp o t i n t h e d o r s a l f i n and a re d sp o t be­
low and a n t e r i o r t o t h e d o r s a l f i n (W inge, 1 9 2 7 ).
M ales w ith th e gene
j m ac u la tu s were s e l e c t e d b e c a u s e , out o f t e n s o f th o u sa n d s o f i n d i v i d u a l s ,
Ma had n e v e r c ro s s e d o v e r t o X and th u s had n e v e r been t r a n s m itt e d t o a f e ­
m ale.
However, E l o f f (1 9 3 2 ), w orking w ith s to c k s e n t t o him by Winge,
c la im s t o have o b ta in e d a c r o s s - o v e r o f gene Ma from Y t o X.
A fem ale he
b e lie v e s t o have t h e c o n s t i t u t i o n XqX ^ a p p e a re d among t h e progeny o f one
o f h is c ro s s e s .
R e s u lts o f t h e b a c k -c ro s s o f t h i s i n d i v i d u a l t o an XqYj^
male have n o t y e t been o b ta in e d .
Winge (1934a) b e lie v e s t h a t when E lo f f
o b ta in s t h e d a ta from h is t e s t c r o s s , he w i l l f in d t h a t he has an XY so m atic
fem ale s i m i l a r t o th o s e w hich Winge has a lr e a d y p ro d u ced .
To r e t u r n t o
W in g e's c r o s s o f homozygous m a le - lik e fem ales t o m ales w ith a m a c u la tu s b e a r in g Y chromosome, o u t o f f i f t y - e i g h t s o n s , t h r e e f a i l e d t o show th e
m acu la tu s f a c t o r .
C o n s id e rin g t h e s t a b i l i t y o f Ma, th e o n ly c o n c lu s io n t o
be drawn was t h a t th e s e m ales la c k e d a Y chromosome.
When t h e XX m ales were
b a c k -c ro s s e d t o t h e i r own d a u g h te rs , o n ly fem ales (107) w ere p ro d u ced .
Some
o f t h e fem a le s showed m ale c h a r a c te r s b u t no c o m p le te ly m ale in d iv id u a ls were
o b se rv e d .
Winge (1934& and b) has c o n tin u e d t o in b re e d XX m ales w ith t h e i r
d a u g h te rs f o r s e v e r a l g e n e r a tio n s .
He f in d s t h a t g r a d u a lly more p h e n o ty p ic
m ales a p p e a r , u n t i l e v e n tu a lly he o b ta in e d p rogeny i n t h e r a t i o o f 1 XX
16
fem ale : 1 XX m a le .
He assum es t h a t i n t h e norm al L e b is te s t h e autosom es
j
|
c o n ta in b o th m ale and fem ale d e te r m in e rs , t h e X chromosome has a fem ale
I te n d e n c y w h ile t h e Y e x e r t s a m ale e f f e c t .
i
Normal m ales have a p lu s sum
f
j
f o r t h e i r s e x -d e te r m in in g genes and t h e fem a le s a n e g a tiv e sum.
The p lu s
; m ale and m inus fem ale genes upon t h e autosom es a r e b a la n c e d so t h a t u n d er
norm al c o n d itio n s th e y do n o t e x e r t any in f lu e n c e upon se x d e te r m in a tio n .
I
The s l i g h t l y m a s c u lin iz e d fem ales may have c o n ta in e d f a i r l y h ig h
I p o s i t i v e m ale a u to so m al d e te rm in e rs w hich o v e r-b a la n c e d th e n e g a tiv e fem ale
genes i n t h e X chromosomes t o such an e x te n t t h a t c o lo r genes borne on th e
X w ere e n a b le d t o e x p re s s th e m se lv e s p h e n o ty p ic a lly .
C o n v ersely , m ales
from t h i s r a c e may c o n ta in p o s i t i v e m ale v a lu e s w hich a r e h ig h e r th a n n o r­
m al.
R ep e ated b a c k - c r o s s in g t o an XX m ale may r e s u l t i n t h e ap p earan ce o f
new XX m a le s, due t o an a c c u m u la tio n o f t h e o f f s p r in g o f t h e l a r g e r number
o f p o s i t i v e m ale a u to so m a l genes c h a r a c t e r i s t i c o f th e s e m a le s.
C ro s s-o v e rs
betw een t h e chromosomes o f t h e XX r a c e o f m ales may r e s u l t i n an a c c u m u la tio n
o f h ig h e r p o s i t i v e v a lu e s upon one p a i r o f autosom es th a n upon th e o th e r s .
I f t h i s o c c u rs , a new mechanism o f se x d e te r m in a tio n w i l l have become e s ­
t a b l i s h e d and t h e fo rm er p a i r o f se x chromosomes w i l l have become e q u iv a le n t
t o au to so m es.
Winge (1934a) p r e d i c t s t h a t f u tu r e i n v e s t i g a t i o n s w i l l show
t h a t new s e x - lin k a g e s have been e s ta b l i s h e d .
I n a d d itio n t o p ro d u c in g XX m a le s, Winge (1934a and b) has been
s u c c e s s f u l i n e s t a b l i s h i n g a l i n e o f XY fem ales and XY m a le s.
A f te r th e
d is c o v e ry o f an XY fe m a le , t h e su b seq u en t p ro ce d u re fo llo w e d t h a t a lr e a d y
o u t lin e d f o r t h e e s ta b lis h m e n t o f an XX r a c e w ith t h e e v e n tu a l p ro d u c tio n
o f a new p a i r o f se x chromosomes.
v i a b l e YY a n im a ls .
Winge i s th e f i r s t t o have o b ta in e d
I n t h i s in s ta n c e th e YY form s a r e m ales and e a s i l y d e -
I
t e c t a b l e p h e n o ty p ic a l l y b e ca u se t h e Y chromosomes a r e m arked by c o lo r c h a r -
i
,
a c t e r s n e v e r knoTm t o have c ro s s e d o v e r.
W itsc h i (1932) d is a g r e e s w ith t h e l o c a t i o n o f a dom inant m ale f a c ­
t o r upon t h e Y chromosomes and s u g g e s ts t h a t th e autosom es e x e r t a m ale and
t h e X chromosomes a fem ale i n f l u e n c e .
fem ale v a lu e .
upon t h e Y.
The Y chromosome may c o n ta in a low
G oldschm idt (1937) o b je c ts t o t h e l o c a t i o n o f a m ale f a c t o r
A lso , he d oes n o t b e lie v e t h a t Winge i s j u s t i f i e d i n a s s uming
; th e p resen ce o f male and fem ale ( - and +) genes upon th e autosomes because
no ev id en ce has been p resen ted t o show which genes are w ithout in flu e n c e
under normal c o n d itio n s .
Moreover, Goldschmidt in te r p r e ts Winge*s th eo ry
i
t o mean th a t many autosom al genes may a c t as m odifyin g f a c to r s upon e it h e r
s e x i f m utated or recombined in a d e f in it e manner.
The on ly d iffe r e n c e be­
tween Winge*s th e o r y and th e th e o r ie s o f th e o ld e r authors i s th a t " th ese
claim ed autosom al m o d ifie r s o n ly when found, whereas Winge in tro d u ces them
in la r g e numbers a p r i o r i . 11 (page 4 3 7 ).
D.
G e n e tic a l A nalyses o f Xiphophorus
Xiphophorus has not been stu d ie d as in t e n s iv e ly as P la ty p o e c ilu s
or L e b is te s and so f a r no s e x -lin k a g e
K e rrig a n (1934) s tu d ie d t h e
X iphophorus h e l l e r i i *
has been d isco v er ed .
c r e s c e n t and tw in s p o t m arkings i n
C resce n t i s i n h e r i t e d as a dom inant au to so m al f a c ­
t o r and i s produced by t h e i n t e r a c t i o n o f t h e f a c t o r C w ith an e x te n s o r P.
Twin sp o t i s p ro d u ced by C w ith o u t t h e e x te n s o r P and n o n -sp o t r e s u l t s from
any co m b in a tio n s o f c , p and P.
I n o th e r w ords, t h e c r e s c e n t p a t t e r n i s
due t o su p p le m e n ta ry f a c t o r s p ro d u c in g c r e s c e n t, tw in sp o t and n o n -sp o t i n
t h e r a t i o o f 9 * 3 :4 -
Gordon (1935) s tu d ie d t h e i n h e r it a n c e o f m icrom elanophores i n
two v a r i e t i e s o f X ip h o p h o ru s, t h e aquarium montezumae and t h e y e llo w sword­
ta il.
The aq u ariu m X iphophorus known a s montezumae i s n o t th e X iphophorus
montezumae d e s c rib e d by Jo rd a n and S n y d er.
The aquarium ty p e i s claim ed
t o have b een o r i g i n a l l y a h y b rid betw een one o f t h e s u b s p e c ie s o f Xipho­
p h o ru s h e l l e r i i H eckel and t h e w ild ty p e X iphophorus montezumae.
As a
consequence o f c o n s ta n t b a c k - c r o s s in g t o X iphophorus h e l l e r i i , many o r i g i n a l
h y b rid c h a r a c t e r s w ere l o s t .
The y e llo w s w o r d ta il i s an aquarium -produced
s t r a i n o f X iphophorus h e l l e r i i .
The y e llo w s w o r d ta il i s r e c e s s iv e t o a l l th e ty p e s o f chrom atop h o re s o c c u r r in g i n t h e m ontezum ae.
X iphophorus montezumae i s c h a r a c te r iz e d
by a f a c t o r Rf f o r t h e e r y t h ro p h o res w hich pro d u ce o ra n g e -re d m argins upon
t h e f i n s , by a f a c t o r Sp f o r t h e m acrom elanophores p ro d u c in g two rows o f
b la c k s p o ts , and by t h e f a c t o r S t f o r t h e m icrom elanophores p ro d u c in g t h e
s tip p le d e f f e c t.
Montezumae (R f Sp S t) X y e llo w s w o r d ta il ( r f sp s t ) g iv e
f o u r ty p e s i n t h e F^ g e n e r a tio n .
Two a r e
l i k e t h e p a r e n t a l t y p e s , (R f r f
Sp sp S t s t ) r e d d is h w ith rows o f b la c k s p o ts l i k e t h e m ontezumae, and
y e llo w ( r f r f sp sp s t s t ) l i k e t h e r e c e s s iv e p a r e n t.
a r e new.
The o th e r two ty p e s
Type number t h r e e i s l i k e t h e w ild g r e y is h - g re e n X iphophorus ( r f
r f sp sp S t s t ) and ty p e number f o u r i s r e d d is h w ith o n ly a t r a c e o f b la c k
s p o t t i n g n e a r t h e head (R f r f Sp sp s t s t ) .
T here i s some i n d i c a t i o n t h a t
Rf and Sp may be s e x - lin k e d and t h a t S t may be au to so m al.
Thus G ordon1s g e n e t i c a l ex p erim en ts show a t l e a s t one o f th e form s
o f X iphophorus t o have s e x - lin k a g e and t h e r e f o r e sex chromosomes.
Gordon
does n o t p r e s e n t h i s r e s u l t s i n enough d e t a i l t o show w h eth er s e x -lin k a g e
i n d i c a t e s s e x d e te r m in a tio n t o be o f t h e A braxas o r o f th e D ro so p h ila ty p e .
19
j E.
I n t e r s p e c i f i c c r o s s e s among t h e P o e c i l i i d a e w ith r e s p e c t t o s e x
d e t e rm in a t i on
Bellam y (1922) o b ta in e d e x tre m e ly abnorm al and v a r i a b l e se x r a t i o s ,
i; i n t e r s exes and s t e r i l e i n d i v i d u a l s when P la ty p o e c ilu s m a c u la tu s was c ro s s e d
w ith X iphophorus h e l l e r i i .
T h ree m atin g s gave i n t h e F-^ g e n e r a tio n s , 8 m ales :
; 1 fe m a le , 0 m ales : 10 fe m a les and 6 m ales : 0 fe m a le s.
The same in c o n s i s -
| t e n c i e s w ere o b se rv e d i n t h e F£ h y b r id s , where one m a tin g gave 12 m ales :
30 fe m a le s and a n o th e r 30 m ales : 5 fe m a le s .
I n 1936 Bellam y p u b lis h e d d a ta c o n c e rn in g i n t e r s p e c i f i c h y b rid s
i n P la ty p o e c ilu s .
P la ty p o e c ilu s m a c u la tu s . a ZZ WZ ty p e was c ro s s e d w ith
; P la ty p o e c ilu s v a r i a t u s . an XX XI form .
B oth t h e w ild ty p e P la ty p o e c ilu s ,
w ith i t s Z chromosome, m arked by a gene f o r w ild t y p e , Zs and th e s p o tte d
o r p u lc h r a ty p e o f P la t y p o e c i l u s , b e a r in g t h e gene f o r s p o tt i n g upon i t s
t Z chromosome (Z p ), were u s e d .
V a r ia tu s X and Y chromosomes were unm arked,
a lth o u g h r e s u l t s seemed t o i n d i c a t e t h a t t h e s t r i p e d components o f t h e w ild
ty p e p a t t e r n o f v a r i a t u s was a s s o c ia t e d w ith th e I chromosome.
The f o u r
c r o s s e s , and t h e r e s u l t s o b ta in e d from them a r e summarized i n t a b u l a r form
on page 20.
B ecause o f t h e u n is e x u a l p ro g en y o b ta in e d from c r o s s A, Bellam y
co n c lu d e s t h a t i n P la ty p o e c ilu s v a r i a t u s t h e m ales a r e h e te ro g a m e tic , and
p o s t u l a t e s t h a t t h e r e i s a se x d i f f e r e n t i a l f o r m alen ess a s s o c ia te d w ith
t h e m a c u la tu s Z and t h e v a r i a t u s Y.
c i a t e d w ith fe m a le n e s s .
C o n v ersely , X and W a p p e a r t o be a s s o ­
Young an im a ls a r e b e lie v e d t o be b i p o t e n t i a l , w ith
m ale and fem ale te n d e n c ie s n e a r e q u ilib r iu m .
Any s e x d i f f e r e n t i a l , w h eth er
i t be b o rn e i n t h e s e x chromosomes o r w h eth er i t be o f e n v iro n m e n ta l o r ig i n ,
i s c a p a b le o f s h i f t i n g t h e e q u ilib r iu m t o one s id e o f t h e s c a le o r t h e o th e r .
20
C ross A
m a c u la tu s
P u lc h ra
zp zp
£
x v a ria tu s 0
-------XX
P henotype
¥
118
ZpX
C ross B
F]_ £ from A x m a c u la tu s £
P u lc h ra
w ild ty p e
ZpX
z sw
33
ZpZg
C ross C
F]_
from A x v a r i a t u s £
-------P u lc h ra
ZpX
XX
A9
ZpX
C ross D
/\
v a r i a t u s 6 x m a c u la tu s £
-------w ild ty p e
XI
ZSW
10
ZSY
0
tsi -P"
C ro sses
£
P u lc h ra dom­
in a n t and
a p p e a rs i n
a l l m ales
-
-
10
wx
P henotype
In te rsex es
---------
0
no s t r i p e s
w ild ty p e
more l i k e
m acu latu s
th a n v a r i ­
a tu s
0
V a r ia b le
p u lc h r a
9
zs x
0
P u lc h ra
0
69 W ild ty p e
XX
0
0
S trip e s
13
z sx
2 No s t r i p e s
WX
or
wr?
1
R eed, Gordon and L a n sin g (1933) have i n v e s t i g a t e d th e i n h e r it a n c e
o f t h e s p o t f a c t o r f o r m acrom elanophores i n c r o s s e s betw een P la ty p o e c ilu s
m a c u la tu s and P . c o u c h ia n u s .
They have d is c o v e re d t h a t h y b rid s i n h e r i t i n g
t h e sp o t f a c t o r d e v elo p m e la n o tic n eo p lasm s.
F our c r o s s e s were made i n ­
v o lv in g P . m a c u la tu s fe m a les h e te ro z y g o u s f o r t h e sp o t f a c t o r , lo c a te d i n
e i t h e r t h e W o r t h e Z chromosomes, and P . co u ch ian u s m a le s.
They o b ta in e d
107 m e la n o tic o f f s p r i n g and 120 norm al h y b rid s ,
P . m a c u la tu s
(ZgpW) x
P. c o u c h ia n u s
P . m a c u la tu s
(3 c r o s s e s )
(ZW« ) x
P . co u ch ian u s
m e la n o tic m ales
norm al fem ales
-----
m e la n o tic fem ales
norm al m ales
3 m e la n o tic m a le s,
c o n s id e re d t o be
c ro ss-o v e r ty p e s .
21
F l h y b rid s w ere in b r e d and p ro d u ced I& norm als and 23 m e la n o tic s .
I n some
o f t h e m e la n o tic f i s h l a r g e n e o p l a s tic a r e a s w ere p r e s e n t on th e day o f t h e i r
b irth .
Gordon (1933) c o n tin u e d h y b r id iz in g s p e c ie s o f P la ty p o e c ilu s ,
s tu d y in g i n h e r i t a n c e o f t h e f a c t o r f o r m acrom elanophores, and i t s r e l a t i o n
t o t h e f a c t o r R f o r r e d body co lo r*
A.
P . m a c u la tu s (ZWgpR) x P . co u ch ian u s
B.
P . m a c u la tu s ( ZWgDp ) x P . x i p h i d i u m
C.
P . m ac u la tu s (ZWgpj^) x P . v a r i a t u s
m e la n o tic d a u g h te rs
sons l i k e f a t h e r
D.
P . m a c u la tu s (ZgpWgp) x X* h e l l e r i i
m e la n o tic d a u g h te rs
and sons
-------
m e la n o tic d a u g h te rs
sons l i k e f a t h e r
m e la n o tic
d a u g h te rs
sons l i k e f a t h e r
The r e s u l t s o f c r o s s D showed t h a t m e la n o tic o vergrow ths a r e i n t e n s i f i e d
when t h e s p o t f a c t o r i s a lo n e r a t h e r th a n co u p led w ith r e d .
S in c e i n t e r ­
se x e s d id n o t a p p e a r, Gordon co n cluded t h a t se x chromosomes dom inate th e
s e x -d e te rm in in g in f lu e n c e s i n t h i s g ro u p .
Reed and Gordon (1931) have i n ­
v e s t i g a t e d th e m orphology o f th e m e la n o tic overgrow ths and have come t o th e
c o n c lu s io n t h a t th e y a r e t r u e n eo p lasm s.
T h e ir ap p earan ce i n t h e h y b rid s
i s i n d i c a t i v e o f m e ta b o lic d is tu r b a n c e s w ith in t h e org an ism , p erh ap s due t o
p h y s io lo g ic a l i n c o m p a t i b i l it y betw een f o r e ig n p ro to p la s m s.
Kosswig has a l s o s tu d ie d th e problem o f h y b r id i z a tio n .
D ata ob­
t a i n e d from c r o s s e s betw een X iphophorus and s e v e r a l s p e c ie s o f P la ty p o e c ilu s
have l e d
him t o co n clu d e t h a t X iphophorus i s a l a t e n t g e n o ty p ic herm aphro­
d i t e , " p h e n o ty p ic a lly 11 se x d e te rm in e d .
I n e x p la n a tio n o f h is te rm in o lo g y ,
K osswig (1935) d e f in e s a p h e n o ty p ic a lly se x d eterm in e d a n im al as one w hich
i n s p i t e o f w e ll d ev e lo p e d seco n d ary s e x c h a r a c te r s i s g e n o ty p ic a lly b i ­
s e x u a l t o su ch an e x te n t t h a t e n v iro n m e n ta l in f lu e n c e s form th e b a s is o f
se x d e te r m in a tio n .
K osswig (1933) c ro s s e d X iphophorus h e l l e r i i and P la ty p o e c ilu s
m a c u la tu s .
C ross 1 .
X iphophorus £ (z z ) x m a c u la tu s / \ z z ) — / / and 9 $ i n Xipho­
phorus r a t i o o f 75
p e r c e n t m ales
C ro ss 2 .
m a c u la tu s 9 (ZW) x
(Zz)
— / </ and 9 9
o f 1 :1
C ro ss 3*
m a c u la tu s /
(Z z)
— a l l /* ^
C ross 4 .
X iphophorus /
(ZZ) x F]_ ^
(z z ) x m a c u la tu s o (ZW)— / c / and 9 9
o f 1 :1
in ra tio
in ra tio
I n a n o th e r s e r i e s o f c r o s s e s w ith P la ty p o e c ilu s Kosswig (1935) s e le c te d a
s t r a i n i n w hich t h e Z chromosome was m arked by t h e gene R f o r re d body c o lo r .
C ro ss 5*
X iphophorus 9 (z z ) x re d m ac u la tu s / (Z^Z^) — r e d £ £ and r e d / /
C ross 6 .
X iphophorus / ( z z ) x F^_ 9
C ross 7«
X iphophorus c / ( z z ) x F2 re d ^ ( % z )
— greyp.? : g r e y / /
and i r e d 9
C ross S.
X iphophorus < / (z z ) x re d maculatus^(ZjjW )
— re d // :
C ross 9*
Red F]_ c /
— 2 r e d / / : 1 re d 9
1 g re y 9
(^Rz )
(Zj^z)
x re<^ m aculatus/Z j^W )
— re d £ £ : rede/ / 1
(more
) and
g re y
: g re y //
(more r f V )
g rey £ 9
On th e b a s i s o f th e s e and o th e r i n t e r g e n e r i c c r o s s e s , Kosswig (1933
and 1935) draws s e v e r a l c o n c lu s io n s c o n c e rn in g t h e se x mechanism o f Xipho­
p h o ru s and P la ty p o e c ilu s :
1.
fe m a le s a p p e a r.
I n C ross 3 , t h e P la ty p o e c ilu s W chromosome i s la c k in g and no
T h e re fo re Kosswig co n clu d es t h a t t h e W chromosome con­
t a i n s fe m a le -d e te rm in in g g en es.
T h is c o n c lu s io n i s b ased upon t h e a s -
23
su m p tio n t h a t X iphophorus has no s e x chromosomes and no se x genes*
Howeveij C ross 4 i n d i c a t e s t h a t one o f t h e X iphophorus chromosomes i s
homologous t o t h e P la ty p o e c ilu s Z, f o r i n t h i s c r o s s Z form s a r e m ales
and W form s a r e fe m a le s .
I n s p i t e o f t h i s seem in g ly c o n tr a d ic to r y
e v id e n c e , K ossw ig b e lie v e s t h a t th e assu m p tio n o f p h e n o ty p ic a l s e x de­
te r m in a tio n i n X iphophorus g iv e s t h e most l i k e l y e x p la n a tio n o f th e
r e s u l t s a s a whole*
a.
His re a s o n s a r e a s fo llo w s :
I n C ro ss 6 , r e d F2 fem ales a p p e a r, w hich would n o t be
p o s s i b l e i f X iphophorus fem ale s w ere ZW.
b.
I n C ross 7> th e s e same r e d F2 fem ales when c ro s s e d t o
t h e X iphophorus m ale pro d u ce b o th g re y m ales and fe m a le s.
I f t h e F2
fem ale c o n ta in e d a W chromosome from X iphophorus a l l t h e m ales s h o u ld
be r e d and a l l t h e fem ales g re y .
c.
B ecau se, i n o th e r g e n e r a tio n s , i n d iv id u a ls a r e produced
c o n ta in in g b o th o f t h e X iphophorus chromosomes ( z z ) , w hich a r e supposed
t o be homologous t o P la ty p o e c ilu s Z chromosomes, and t h e s e i n d iv id u a l s
a r e of b o th s e x e s .
2.
som es.
Male d e te rm in e rs i n P la ty p o e c ilu s a r e lo c a te d upon th e a u to When t h e F^_ o f C ross 1 a r e m ated, ZZ x ZZ, presum ably t h r e e
g en o ty p es a r e p o s s i b l e , ZZ, Zz and z z .
F is h o f zz c o n s t i t u t i o n a r e
l i k e p u re X iphophorus and y e t , among th e s e fo rm s, t h e p r o p o r tio n o f
m ales t o fe m a le s i s much h ig h e r th a n n o rm a lly found i n p u re zz X i­
phophorus s to c k s .
T h e re f o re , t h e P la ty p o e c ilu s autosom es i n t h i s zz
h y b rid m ust be e x e r t i n g a m ale in f lu e n c e .
3.
I n C ross 1 , t h e p ro g en y , su p p o sed ly a l l g e n o ty p ic a lly Zz,
fo llo w t h e t y p i c a l X iphophorus sex r a t i o o f 3 m ales : 1 fe m a le .
Be-
ca u se o f t h i s r a t i o , K ossw ig assum es t h a t p h e n o ty p ic a l sex d e te rm in a ­
t i o n i s dom inant o v e r t h e g e n o ty p ic t y p e , r e p r e s e n te d i n t h i s c ase by
t h e P l a ty p o e c ilu s Z chromosome.
S in ce se x chromosomes and se x genes
a r e assum ed t o be la c k in g i n X iphophorus, t h e a n la g e f o r p h e n o ty p ic
se x d e te r m in a tio n i s i n h e r i t e d w ith in th e p ro to p la sm and, m oreover,
t h e Z chromosome i s assum ed t o be i n h i b i t e d by t h e f o r e ig n obplasm .
I n t h e r e c i p r o c a l c r o s s , how ever, (C ro ss X) t h e r a t i o o f m ales t o f e ­
m ales i s 1 : 1 .
A gain t h e h y b rid s a r e g e n o ty p ic a lly Zz.
Here i t i s
assum ed t h a t , b ec au se i n t h i s c a se t h e o8p lasm i s c o n tr ib u te d by P la ty ­
p o e c ilu s i n s t e a d o f X ip h o p h o ru s, t h e Z and W chromosomes a r e a b le t o
o p e r a te n o rm a lly , and t h e g e n o ty p ic ty p e o f se x d e te r m in a tio n i s
dom inant •
Kosswig (1933) makes t h e fo llo w in g g e n e r a li z a tio n s c o n c e rn in g
se x d e te r m in a tio n i n P la ty p o e c ilu s - X iphophorus h y b r id s .
1.
Sex d e te r m in a tio n (when th e oBplasm o r i g i n a t e s from Xipho­
p h o ru s) f o llo w s t h e X iphophorus ty p e :
a.
When a f u l l X iphophorus genotype i s p r e s e n t;
b.
When more th a n a f u l l X iphophorus genotype i s p r e s e n t;
c.
When d e f i n i t e X iphophorus chromosomes a r e p r e s e n t i n a
homozygous c o n d itio n i n a p r e p o n d e ra n tly P la ty p o e c ilu s h e r e d i ta r y
com plex.
2.
S ex d e te r m in a tio n fo llo w s t h e P la ty p o e c ilu s ty p e when th e
f i s h p o s s e s s e s more th a n a f u l l P la ty p o e c ilu s gene complex.
G oldschm idt (1937) b e lie v e s t h a t a l l o f K ossw ig’ s d a ta may be
i n t e r p r e t e d by a p p ly in g t h e fo rm u la w hich s u c c e s s f u lly e x p la in s se x d e te r ­
m in a tio n i n L y m a n tria, Amphibia and D ro s o p h ila .
P la ty p o e c ilu s i s assumed
25
t o be s i m i l a r t o t h e d i f f e r e n t i a t e d r a c e s o f f ro g s and s in c e i t i s h e te r o g am etic i n t h e fem ale r a t h e r th a n i n th e m ale, fem ale (FF) r a t h e r th a n
m ale (MM) d e te r m in e rs a r e l o c a t e d upon t h e au to so m es.
S tro n g m ale (M str)
f a c t o r s a r e assum ed t o be on t h e Z chromosomes and no s e x f a c t o r s (m) upon
th e W.
I n su ch a c a se FF>M<MM,
Thus t h e fo rm u lae f o r P la ty p o e c ilu s
m ales and fe m a le s a r e a s fo llo w s :
FF M str M
s tr
m ale
FF M str m
fem ale
X iphophorus i s compared t o th e u n d i f f e r e n t i a t e d r a c e s o f f ro g s
and i s assum ed t o p o s s e s s fem ale digam ety a s does P la ty p o e c ilu s ,
A gain
(FF) fem ale f a c t o r s a r e c a r r i e d i n t h e autosom es and th e Z chromosomes
b e a r r e l a t i v e l y weak m a le -d e te rm in e rs (Mw).
The W chromosome b e a r s a m ale
gene whose p o te n c y v a r i e s i n d i f f e r e n t r a c e s o f v a r y in g d e g re e s o f d i f f e r ­
e n tia tio n ,
T hus, r a c e s o f X iphophorus may c o n ta in M genes on t h e W, g rad ­
in g i n i n t e n s i t y from M - Ml - M 2
m.
On t h i s b a s is a r a c e o f Xipho­
p h o ru s m ight have t h e fo llo w in g fo rm u lae:
FF
Mw
Mw
--------
FF
Mw
Ml
-------
m ale
fem ale
G oldschm idt s u c c e s s f u l l y a p p lie s t h e s e fo rm u lae t o a m a jo r ity o f th e c r o s s e s
made by K ossw ig.
F o r p u rp o se s o f i l l u s t r a t i o n i t m ight be w e ll t o show
G o ld sch m id t’ s i n t e r p r e t a t i o n o f one c r o s s .
C ross 1 (K ossw ig) •
X iphophorus £
x P. m acu latu s
— m ales and f e ­
m ales i n a t y p i c a l
X iphophorus r a t i o .
K ossw ig, o f c o u rs e , assum ed dom inance o f th e p h e n o ty p ic ty p e o f se x d e t e r ­
m in a tio n .
Such a n assu m p tio n i s u n n e c e s sa ry when th e r e s u l t s a r e i n t e r ­
p r e t e d a c c o rd in g t o G o ld sch m id t’ s th e o r y .
26
X iphophorus
FF Mw Ml
(ZW)
x
P . m a c u la tu s
x
FF M str M str
(ZZ)
J (FFMW M str) m ales
and J (FFM1 M str) fe m a le s w ith a s tr o n g m ale te n d e n c y , s tr o n g e r th a n
i n X iphophorus (MIAMI) and th u s much se x tr a n s f o r m a tio n .
A cco rd in g t o G oldschm idt (1 9 2 7 ), B r e id e r c ro s s e d t h r e e s p e c ie s o f
L im ia, nam ely, L in d a v i t t a t a . L. n i g r o f a s c i a t a and L. c a u d a ta .
He o b ta in e d
v a r y in g p r o p o r tio n s o f m ales and fem a le s from a v a r i e t y o f c r o s s e s and used
a l l o f K ossw ig’ s a ssu m p tio n s t o e x p la in h is r e s u l t s :
1.
From t h e r e s u l t s o f a c r o s s betw een Lim ia c a u d a ta and L. n i -
g r o f a s c i a t a i n w hich o n ly m ales were p ro d u ced , he co ncluded t h a t Lim ia
n i g r o f a s c i a t a was o f XX-XY c o n s t i t u t i o n and Lim ia c a u d a ta was s im i l a r
t o X ip h o p h o ru s, h av in g p h e n o ty p ic s e x d e te r m in a tio n .
L a te r c r o s s e s
were assum ed t o show Lim ia v i t t a t a t o be l i k e L. c a u d a ta *
2.
To e x p la in t h e r e s u l t s o f a l l t h e r e s t o f h is c r o s s e s he em­
p lo y e d a l l o f K ossw ig1s a s su m p tio n s, such a s :
a.
Dominance o f one ty p e o f se x d e te r m in a tio n o v er t h e o th e r .
b.
M u ltip le au to so m al m ale d e te r m in e rs .
c.
I n f lu e n c e o f odplasm upon se x d e te r m in a tio n .
d.
Empty X-chromosomes and m ale—d e te rm in e rs i n t h e Y-chromosome.
G oldschm idt m a in ta in s t h a t B r e id e r ’ s r e s u l t s , l i k e th o s e o f Koss­
w ig , f a l l i n t o l i n e w ith o th e r work upon f i s h w ith o u t in tr o d u c in g any new
and c o m p lic a tin g p o s t u l a t i o n s .
The few s p e c i a l f e a t u r e s may be e x p la in e d
on t h e b a s i s o f c r o s s - o v e r o r l e t h a l e f f e c t s .
F.
C o n clu sio n s
G e n e tic a l i n v e s t i g a t i o n s upon A p lo c h e ilu s , L e b is te s , L im ia, and
27
X iphophorus have shown t h a t t h e h e r e d i t a r y mechanisms o p e r a tin g w ith in t h e
group a r e v e r y s i m i l a r ,
1#
I n a l l fo rm s, ex c ep t X iphophorus h e l l e r i i , th e m a jo r ity o f
t e s t e d c o lo r genes have been shown t o be s e x - lin k e d .
I n L e b is te s ,
s e v e n te e n o u t o f e ig h te e n t e s t e d c o lo r genes show s e x - lin k a g e .
2.
I n a l l o f t h e g e n e ra s tu d i e d , ex cep t X iphophorus, c r o s s - o v e r
o c c u rs betw een t h e X and X o r Z and W chromosomes.
3.
S tu d ie s upon s e x -lih k a g e have shown t h a t b o th th e A braxas ty p e
o f s e x d e te r m in a tio n and t h e D ro so p h ila ty p e e x i s t w ith in a s in g le sub­
f a m ily .
4.
I n t e r s p e c i f i c c r o s s e s i n d i c a t e t h a t t h e sex d e te rm in in g me­
chanism i s r e l a t i v e l y u n s ta b le , p a r t i c u l a r l y i n X iphophorus.
5.
W ith t h e e x c e p tio n o f K ossw igTs th e o r y o f se x d e te r m in a tio n ,
th o s e o f W Its c h i, G oldsch m id t, B ellam y, A id a, and Winge, w h ile th e y
d i f f e r i n numerous d e t a i l s , a g r e e t o t h e e x te n t t h a t th e y a l l e x p la in
s e x d e te r m in a tio n by assum ing a q u a n t i t a t i v e b a la n c e betw een t h e sex
d e te rm in e rs upon t h e autosom es and th o s e upon one o r b o th o f th e sex
c h r omo some s •
6.
Winge has shown t h a t se x chromosomes may be tra n s fo rm e d i n t o
autosom es and autosom es i n t o s e x chromosomes.
T h is would seem t o i n ­
d i c a t e t h a t , p h y s io l o g i c a l l y , a t l e a s t , heterochrom osom es a r e n o t w e ll
d i f f e r e n t i a t e d , and le n d s su p p o rt t o W its c h iTs (1932) s u g g e s tio n , t h a t
t e l e o s t e a n s e x chromosomes ve x h ib it e a r l y p h ases i n t h e e v o lu tio n o f
chromosomal mechanisms o f s e x d e te r m in a tio n .1” (page 2 0 7 ).
G e n e tic a l e v id en c e o f s e x -lin k a g e i n d i c a t e s t h a t t h e germ c e l l s
o f t h e P o e c i l i i d s may c o n ta in i d e n t i f i a b l e sex chromosomes.
On th e o th e r
28
hand, e v id e n c e f o r t h e e x is te n c e o f d i f f e r e n t i a t e d and u n d i f f e r e n t i a t e d
r a c e s o f f i s h , e v id e n c e f o r o n e -s id e d m ascu li n e and o n e -s id e d fem in in e i n ­
h e r i ta n c e w ith in a s in g l e s u b -fa m ily , ev id e n c e o f tr a n s f o r m a tio n o f sex
chromosomes i n t o autosom es and v ic e v e r s a , and ev id en ce o f l a t e n t herma­
p h r o d itis m , p o in t t o t h e p o s s i b i l i t y t h a t
heterochrom osom es have not y e t
become d i s t i n g u i s h a b l e from au to so m es.
However, t h e v e r y e x is te n c e o f th e s e tyro l i n e s o f c o n f l i c t i n g
ev id e n c e n o t o n ly i n d i c a t e s th e need f o r e x te n s iv e c y to lo g ic a l r e s e a r c h ,
b u t may s tim u la te t h e i n t e r e s t s o f c y t o l o g i s t s t o overcome t h e i r u n d e r­
s ta n d a b le r e lu c ta n c e t o s tu d y t h e t e l e o s t germ c e l l s w ith t h e i r s m a ll and
numerous chromosomes,
C y to lo g ic a l S tu d ie s upon T e le o s te a n Germ C e lls
B efo re ex am in in g t h e c y to l o g i c a l l i t e r a t u r e c o n c e rn in g t e l e o s t e a n
h e te r o chromosomes, i t m ight be w e ll t o rev iew b r i e f l y some l i t e r a t u r e con­
c e rn e d w ith t h e m orphology and b e h a v io r o f se x chromosomes i n g e n e r a l, i n
o r d e r t o e s t a b l i s h a s e t o f e f f e c t i v e c r i t e r i a f o r d i s ti n g u i s h in g them ,
McClung (1899) 9 w orking upon th e male germ c e l l s o f some s p e c ie s
o f t h e fa m ily L o c u s tid a e , d e s c r ib e s what he te rm s 11a
p e c u l i a r n u c le a r e l e ­
m ent” (page l ) :
a.
The elem ent f i r s t a p p e a rs upon th e s u r f a c e o f th e n u c le a r
v e s i c l e o f t h e sperm atogonium .
b.
B efo re t h e sp e rra a to g o n ia l d i v i s i o n , t h e n u c le a r elem ent be­
came t h r e a d - l i k e and U -sh ap ed ,
t h e tim e
c.
D iv is io n t a k e s p la c e i n l a t e an ap h a se .
d.
D uring t h e s y n a p tic s ta g e s , i t rem ains t o one s id e , but a t
t h e chromosomes e n t e r th e d i a k in e s i s s ta g e , i t s h o rte n s t o form a
29
U -sh ap ed t e t r a d .
e.
D u rin g t h e p rim a ry sp e rm a to c y te d i v i s i o n , th e a c c e s s o ry ch ro ­
mosome l i e s o u ts id e o f t h e group o f chromosomes upon t h e e q u a t o r ia l p l a t e ,
d iv id e s d u r in g a n ap h a se , and fo llo w s th e r e s t o f t h e chromosomes t o t h e p o le .
McClung (1900) d e s c r ib e s a s i m i l a r n u c le a r elem ent i n some o f
t h e A c r id id a e .
The chromosome i n t h i s c a se l i e s w ith in i t s own v e s i c l e
u n t i l t h e m etap h ase s ta g e i s re a c h e d .
D uring th e m etap h ase, th e a c c e s s o ry
chromosome i s i n d i s t i n g u i s h a b l e from th e autosom es.
I n 1902, McClung s u g g e ste d t h a t t h e a c c e s s o r y chromosome may be
se x d e te r m in a n t, and l i s t e d t h r e e c r i t e r i a f o r r e c o g n iz in g i t .
1*
A s e x chromosome may be re c o g n iz e d by i t s s ta i n i n g r e a c ti o n
and by t h e d i f f e r e n c e s betw een i t s developm ent and t h a t o f th e a u to ­
somes i n t h e sp e rm a to g o n ia .
2.
I t shows a te n d e n c y t o l a g b eh in d th e o th e r chromosomes.
3.
D uring a l l s ta g e s , ex cep t a c t u a l d i v i s i o n , i t i s e n c lo s e d
w ith in i t s own membrane.
I n 1918 he w ro te t h a t , p erh a p s due t o la g g in g upon th e m etaphase
p l a t e , i t was d i s t r i b u t e d t o o n ly h a l f o f t h e ova.
Up u n t i l 1934 "the amount o f work done upon t h e chromosomes o f
t e l e o s t s was r a t h e r l i m i t e d .
D u ring t h e l a s t f iv e y e a r s , however, th e
p roblem has b een r e c e i v i n g much more a t t e n t i o n .
I n r e s p e c t t o sex chromosomes, th e c y t o l o g i s t s a r e i n d is a g r e e ­
ment^ t h e b u lk o f accu m u lated e v id e n c e , however, i s a g a in s t th e p re se n c e
o f i d e n t i f i a b l e s e x chromosomes i n t h e germ c e l l s o f t e l e o s t s .
S a jir o
Makino and A lex an d ra P ro k o fie v a have done most o f th e work upon t e l e o s t s ,
o th e r th a n t h e C y p rin o d o n te s.
Makino (1933-1934) worked upon two s p e c ie s
o f s t i c k e l b a c k s , P u n g itiu s ty m e n sis and P . p u n g i t i u s . and found no ev id en ce
a t a l l f o r heterochrom osom es i n e i t h e r s p e c i e s .
I n 1937 he re a c h e d th e
same c o n c lu s io n a f t e r ex am in in g t h e germ c e l l s o f t h e lo a c h , M isg u rin a ang u i l l i c a u d a t u s , t h e salm on Qncorhvnchus k e t a , and o f P h o lis p ic tu s and Hexagrammes octogram m us.
P ro k o fie v a (1934) s tu d ie d chromosomes i n s p e c ie s o f
f i s h b e lo n g in g t o t h e g e n e ra Salmo and C oregonus, a s w e ll as i n t h e h y b rid s
betw een s p e c ie s o f Salmo and S a lv e lin u s f o n t i n a l i s and betw een s p e c ie s o f
Coregonus and S a lv e lin u s f o n t i n a l i s .
He o b serv ed no se x chromosomes*
Ka-
toyma (1937) i n v e s t i g a t e d p o s s i b l e se x chromosomes i n A p lo c h e ilu s and ob­
t a i n e d n e g a tiv e r e s u l t s .
I r i k i ( 1932) a ls o made a s tu d y o f t h e s e x chromo­
somes o f A p lo c h e ilu s w ith o u t o b s e rv in g h e te r o chromosomes.
He claim s t h a t
chromosomes com parable t o th o s e d e s c rib e d a s se x chromosomes by G e is e r and
V aupel w ere o b se rv e d i n h i s m a t e r ia l i f i t was p o o rly f ix e d .
I r i k i (1932a)
made a s tu d y o f L e b is te s chromosomes b u t was u n ab le t o i d e n t i f y th e chromo­
somes w hich G e is e r (1924) had d e s c rib e d .
Winge (1922a) exam ined L e b is te s
c y t o l o g i c a l l y w ith o u t b e in g a b le t o d e te c t heterochrom osom es.
He claim s
t h a t c e l l s do n o t become s e p a r a te d a f t e r th e p rim a ry sp erm ato cy te d iv is io n
so t h a t t h e r e a r e no sec o n d a ry sp e rm a to c y te s form ed,
Winge (1922a) s t a t e s :
11A v e r y c h a r a c t e r i s t i c f e a t u r e i s t h e a b s o lu te la c k o f s ta g e s w hich may be
c a l l e d s y n a p s is and d i a k i n e s i s .
At most a f a i n t d e p o s it o f ch ro m atin may
be o b serv ed a s a co m p en satio n f o r t h e s y n a p s i s .11 (page 1 4 l)«
Friedm an and
Gordon (1934) i n v e s t i g a t e d P la ty p o e c ilu s b u t were u n ab le t o o b ta in ev id en ce
f o r s e x chromosomes.
They do n o t b e lie v e t h a t R a ls to n (1934) has demon­
s t r a t e d t h a t a p a i r o f chromosomes p re c e d in g th e chromosomes upon th e m eta­
p h ase p l a t e a r e se x chromosomes.
Even i f su ch chromosomes a r e c o n s i s t e n t l y
p r e s e n t , a c y t o l o g i c a l e x a m in a tio n o f b o th sex es would be n e c e s s a ry b e fo re
31 ,
c o n c lu s io n s c o u ld be draw n.
F o le y , B e n n in g to n , G e is e r, V aupel and R a ls to n b e lie v e th e y have
o b ta in e d e v id e n c e f o r s e x chromosomes.
F o le y (1926) s tu d ie d sperm atogene­
s i s i n Umbra l i m i . an d c o n s i s t e n t l y found i n a l l t h e sp e rm a to g o n ia l c e l l s
a l a r g e L—shaped chromosome, r e l a t i v e l y c o n s ta n t i n s iz e and sh ap e.
b e l ie v e s i t may be t h e s e x chromosome.
He
B ennington (1936) i n h is p a p e r upon
s p e rm a to g e n e s is i n t h e S iam ese f i g h t i n g f i s h , B e tta s p le n d e n s . s a y s , " In
sp e rm a to g o n ia l d i v i s i o n s t h e chromosomes a r e n o t d i s t r i b u t e d e q u a lly upon
th e e q u a to ria l p la te .
Two, much l a r g e r th a n th e o th e r chromosomes, p o s s i­
b ly r e p r e s e n t se x chrom osom es.” (page 1 0 5 ).
T h is same chromosome la g s upon
t h e e q u a t o r i a l p l a t e i n t h e p rim a ry sp e rm a to c y te d i v i s i o n , d iv id in g l a t e r
th a n t h e o th e r chromosomes.
G e is e r (1924) w r ite s i n h i s p a p e r upon Gambusia
h o lb r o o k i i ; '"Lagging chromosomes a r e f r e q u e n tly se e n i n an ap h ase s ta g e s
view ed from t h e s i d e , b u t n o t c o n s ta n tly enough t o g iv e a c lu e as t o t h e
num ber, s i z e and form o f p o s s ib le heterochrom osom es" (page 1&7) •
V aupel
(1929) has a l s o se e n a p a i r o f m etaphase chromosomes i n L e b is te s , w hich p a ss
t o t h e p o le s ah ead o f t h e o t h e r s .
She i n t e r p r e t s th e s e a s p o s s ib le se x ch ro ­
mosomes i n P l a t y p o e c i l u s , i n X ip h ophorus, and i n t h e P la ty p o e c ilu s -X ip h o p h o ru s h y b r id s .
They p re c e d e th e r e s t o f t h e chromosomes t o th e p o le s .
T hus, th ro u g h t h e work o f R a ls to n on P la ty p o e c ilu s and X iphophorus,
G e is e r on Gam busia, and V au p el on L e b is te s , i t seems p ro b a b le t h a t th e p o e c i l i i d s p o s s e s s a p a i r o f se x chromosomes, w hich a r e most e a s i l y o b serv ed
i n t h e m etap h ase o f t h e p rim a ry sp e rm a to c y te d iv i s io n .
S in c e th e p re se n c e
o f s e x chromosomes seems t o be f a i r l y w e ll e s ta b lis h e d , f o r th e s e p o e c i l i i d s ,
i t w i l l be i n t e r e s t i n g t o d is c o v e r w h eth er th e y a r e common t o many s p e c ie s ,
o r t o j u s t a few .
MATERIALS AND METHODS
III.
S ource o f M a te r ia l
The tw e n ty s p e c ie s o f P o e c i l i i d a e u se d i n t h i s s tu d y were o b ta in e d
from s e v e r a l s o u rc e s .
T h ree s p e c ie s had been c o lle c te d and f ix e d by Dr.
C. L. T u rn e r i n t h e f i e l d i n Mexico and f i v e were o b ta in e d from s to c k s main­
t a i n e d by D r. T u rn e r i n h i s la b o r a t o r y .
D r. C. L. Hubbs c o n tr ib u te d m ales
o f s i x s p e c ie s an d , i n a d d i t i o n , specim ens o f s i x more s p e c ie s were p u r­
ch ased from t h e E v e rg la d e s A q u a tic N u r s e r ie s i n Tampa, F lo r id a and sh ip p ed
a l i v e t o E v a n sto n .
B ecause t h o s e c y t o l o g i s t s who have d e s c rib e d heterochrom osom es
i n t e l e o s t m a t e r ia l f in d t h a t th e y a r e m ost e a s i l y s tu d ie d d u rin g th e m eta­
p h ase p h ase o f t h e p rim a ry sp e rm a to c y te d i v i s i o n , o n ly m ale specim ens were
used.
Of c o u rs e , i n a l l p r o b a b i l i t y , t h e p rim a ry o d cy te d i v i s i o n would
prove e q u a lly v a lu a b le , ex c ep t f o r t h e f a c t t h a t , so f a r a s i s known, t h e
p rim a ry o d c y te d i v i s i o n t a k e s p la c e v e r y q u ic k ly f o llo w in g f e r t i l i z a t i o n ,
so t h a t i t i s d i f f i c u l t t o c a tc h t h a t s ta g e o f te n enough t o p ro v id e th e
abundance o f m a t e r i a l n e c e s s a r y f o r s tu d y .
P r e p a r a tio n o f S lid e s
A nim als w ere k i l l e d by im m ersion i n B ouin' s f l u i d and were allow ed
t o rem ain im m ersed i n t h e f i x a t i v e w h ile t h e gonads were removed.
The t e s ­
t e s , upon re m o v al, w ere p la c e d i n sm a ll p r o p e rly la b e le d v i a l s o f f i x a t i v e
f o r from e ig h t t o tw e lv e h o u rs .
C are was ta k e n t o u se a volume o f B o u in 's
a t l e a s t t e n tim e s a s g r e a t a s t h e e s tim a te d volume o f th e t e s t e s .
A ll o f
t h e sp e cim e n s, w ith t h e e x c e p tio n o f th o s e f ix e d i n t h e f i e l d and re c e iv e d
i n 70 p e r c e n t a lc o h o l, w ere tr e a .te d i n t h i s m anner.
F o llo w in g f i x a t i o n , t h e gonads r e c e iv e d t h r e e o r fo u r washes o f
50 p e r c e n t a l c o h o l , w ere removed t o 70 p e r c e n t f o r two hours and f i n a l l y
p la c e d i n d io x a n e o v e r n i g h t .
A lth o u g h t h e u se o f dioxane i s supposed to
p r e c lu d e t h e u se o f a c l e a r i n g a g e n t, b e t t e r r e s u l t s were o b ta in e d i f th e
t i s s u e had been c le a r e d i n c e d a r o i l f o r two hours a f t e r rem oval from d io x an e.
E xcess c e d a r o i l was removed by a wash o f x y l o l and t h e t i s s u e s p la c e d i n
p a ra ffin .
F our o r f i v e changes o f p a r a f f i n were fo llo w e d by im bedding.
S in c e o n ly m ales w ere u s e d , i t was p o s s ib le t o sav e tim e by im bedding fo u r
o r f i v e specim ens o f a s in g l e s p e c ie s i n one b lo c k .
B oth t r a n s v e r s e and s a g i t t a l s e c tio n s o f th e t e s t e s were c u t two
o r f o u r m ic ra i n t h i c k n e s s .
S a g i t t a l s e c tio n s were th e more v a lu a b le be­
cau se more c e l l s c o u ld be o b serv ed on a g iv en s e c tio n and becau se t h e gonads
o f m ost o f t h e m ales w ere e lo n g a te d and co u ld be s e c tio n e d more q u ic k ly when
cu t p a r a l l e l t o th e lo n g itu d in a l a x is .
S t a i n i n g was a cco m p lish ed by th e u se o f H eidenhain*s i r o n hema­
t o x y l i n i n aqueous s o l u t i o n .
A f te r p r e lim in a r y tre a tm e n t I n 4 p e r c e n t ir o n
alum f o r tw e n ty - f o u r h o u rs , t h e s l i d e s were s ta in e d f o r a s im i l a r le n g th o f
tim e .
S e c tio n s w ere d e s ta in e d f o r a p p ro x im a te ly one hour i n a s a tu r a te d
s o lu t i o n o f p i c r i c a c id i n 95 p e r c e n t a lc o h o l.
O v e rs ta in in g w ith a conse­
q u e n tly lo n g e r p e r io d o f d e s ta in i n g gave th e b e t t e r r e s u l t s .
D e sta in e d
m a t e r i a l was w ashed r e p e a te d ly i n c l e a r 95 p e r c e n t a lc o h o l, f o r o th e rw ise
t h e p i c r i c a c i d c r y s t a l l i z e d upon t h e s l i d e s and d e s tro y e d t h e i r u s e f u ln e s s .
An e x tre m e ly d i l u t e a l c o h o l i c s o l u t i o n o f p o ta ssiu m a c e t a t e was employed to
b r in g back t h e b lu e c o lo r t o t h e s e c tio n s .
The p i c r i c a c id method of de­
s t a i n i n g a llo w s one t o c o n t r o l t h e end p o in t o f s t a i n rem oval much more a c ­
c u r a t e l y th a n when u s in g a weak s o lu t i o n o f i r o n alum .
S in ce th e a c t io n o f
p i c r i c a c id i s so v e r y much slo w e r th a n t h a t o f i r o n alum , s l i d e s may be ob-
s e rv e d a number o f tim e s b e fo re th e y become e x c e s s iv e ly d e s ta in e d .
If
s l i d e s a r e t e m p o r a r ily m ounted i n a medium o f c e d a r o i l , th e d eg ree o f d e s t a i n i n g can be checked q u ic k ly and a c c u r a te ly th ro u g h o b s e rv a tio n o f i n d i ­
v id u a l c e l l s u n d e r o i l im m ersion.
O b s e rv a tio n s w ere made u s in g a 100X o i l im m ersion o b je c tiv e w ith
15 and 20X o c u l a r s .
Drawings w ere made w ith an Abbe camera l u c id a upon a
draw in g b o a rd e le v a te d a c o n s ta n t d is ta n c e above t h e t a b l e l e v e l .
Thus th e
m a g n if ic a tio n o f a l l c e l l s i s t h e same.
M easurem ents o f Heterochromosomes
The heterochrom osom es d u rin g t h e p rim a ry sp e rm ato cy te d iv i s io n
a r e i s o l a t e d from t h e o th e r chromosomes grouped upon th e m etaphase p l a t e .
B ecause o f t h i s f o r t u n a t e o c c u rre n c e , i t i s p o s s ib le t o m easure them , and
t o t r e a t su ch m easurem ents s t a t i s t i c a l l y , i n o r d e r t o d ete rm in e w h eth er
b o th members o f t h e p a i r a r e r e l a t i v e l y th e same o r d i f f e r e n t I n s i z e .
In
o th e r g ro u p s, i t has been e s t a b l i s h e d , b o th g e n e t i c a l l y and c y t o l o g i c a l l y ,
t h a t i f se x chromosomes i n t h e m ales a re u n lik e i n s i z e , th e a n im als a r e o f
t h e XX - XY t y p e .
I f th e re i s
no d if f e r e n c e i n s iz e betw een th e m ale sex
chromosomes, th e y may be o f t h e ZZ, ZW ty p e ,
XT g ro u p .
o r p h y s io lo g ic a lly i n t h e XX -
F o r t h e p u rp o se s o f t h i s s tu d y i t i s n o t im p o rta n t t o know t h e
e x a c t s iz e o f t h e i n d i v i d u a l members o f a p a i r o f h e te ro chromosomes, n o r t o
know t h e e x a c t m agnitude o f d i f f e r e n c e betw een them , i f one i s found.
The
w r i t e r m e re ly w ish es t o f i n d o u t w hether t h e r e i s , o r i s n o t, a d if f e r e n c e
in s iz e .
I t soon became a p p a r e n t, a f t e r c o n s id e r a tio n o f th e fo llo w in g
t e c h n i c a l d i f f i c u l t i e s , t h a t s t a t i s t i c a l tre a tm e n t o f t h e m easurem ents was
a d v is a b le :
1.
H eterochrom osom es i n a g iv en c e l l may be whole o r s e c tio n e d .
T hus, even i n a s p e c ie s w ith heterochrom osom es o f e q u a l s i z e , s l i g h t d i f ­
f e r e n c e s a s a r e s u l t o f s e c t io n i n g may be o b se rv e d .
However, a la r g e d i f ­
f e r e n c e due t o extrem e s e c tio n in g o f one heterochrom osom e and n o t t h e o th e r
i s s e e n o n ly i n r a r e i n s t a n c e s .
The e x p la n a tio n i s d o u b tle s s t h a t t h e g e m
c e l l s a r e s m a ll and t h e s e chromosomes a r e q u it e c lo s e to g e t h e r , so t h a t I n
most c a s e s when t h e y a r e s e c tio n e d , b o th chromosomes seem t o be c u t a lo n g
th e same p la n e and t o a p p ro x im a te ly th e same d e g re e .
The elem ent o f s e c ­
t i o n i n g , be i t s l i g h t o r g r e a t , makes i t v e r y d i f f i c u l t t o d e c id e upon th e
b a s is o f o p t i c a l e v id e n c e a lo n e , w h eth er o r n o t t h e heterochrom osom es o f a
s p e c ie s a r e m o rp h o lo g ic a lly l i k e o r u n lik e .
O b s e rv a tio n s need t o be s u p p le ­
m ented by m easurem ents o f a f a i r l y la r g e number o f chromosomes.
2.
Due t o s e c tio n in g , t o d if f e r e n c e s i n th e o r i e n t a t i o n
o fc e l l s
w ith in a s in g l e c y s t , and t o s i m i l a r i t y i n shape betw een th e heterochrom o­
som es, i t i s im p o s s ib le t o i d e n t i f y a g iv en heterochrom osom e th ro u g h o u t a
s e rie s of c e lls .
I n o th e r w ords, i f chromosomes A and B o f one c e l l and
chromosomes Aq and Bq o f a n o th e r c e l l a r e m easured, and t h e m easurem ents
show a d i f f e r e n c e i n s iz e betw een A and B and betw een Aq and B q , t h e r e i s
no way o f d e te rm in in g th ro u g h o b s e rv a tio n w h eth er chromosome A o f c e l l No* 1
c o rre sp o n d s t o chromosome Aq o r t o chromosome Bq i n c e l l No. 2.
3.
An a p p a re n t s iz e d if f e r e n c e may be a c c o u n te d f o r ,
i n some i n ­
s ta n c e s , by s l i g h t e r r o r s i n judgment o f th e maximum f o c a l p o i n t .
T h ere a r e s e v e r a l ways o f t r e a t i n g t h e m easurem ents a f t e r th e y
a r e o b ta in e d .
The fo llo w in g method was su g g e ste d by D r. F. A. Brown, J r .
b e c a u se t h e fe w e st p o s s ib le a ssu m p tio n s were r e q u ir e d i n o rd e r t o employ
I t and t h e t e c h n i c a l d i f f i c u l t i e s were m inim ized t o th e g r e a t e s t e x te n t .
1.
D raw ings were made w ith th e cam era lu c id a upon a draw ing board
o f c o n s ta n t h e ig h t.
The draw ing o f each chromosome was m easured w ith a
v e rn ie r c a lip e r.
2.
Each h e te r o chromosome was drawn t e n tim e s , c o m p le te ly r e fo c u s in g
a f t e r eac h d raw in g .
By t h i s m eans, e r r o r s i n judgm ent o f th e maximum f o c a l
p o in t te n d e d t o be c a n c e lle d .
3.
The le n g th o f eac h chromosome was c o n s id e re d t o be th e av erag e
f o r t h e m easurem ents o f t e n d ra w in g s.
4.
F i f t y p a i r s o f chromosomes were t r e a t e d i n t h i s m anner, w ith
t h e r e s u l t t h a t a s e t o f a v erag e m easurem ents f o r one hundred chromosomes
was o b ta in e d f o r each o f tw e n ty s p e c ie s .
5.
A lte r n a te s e c tio n s o f c y s ts o f c e l l s i n t h e p rim a ry sperm ato­
c y te d i v i s i o n w ere u sed t o e x clu d e th e p o s s i b i l i t y o f m easu rin g s u c c e s s iv e
s e c tio n s o f a s i n g l e p a i r o f heterochrom osom es.
6.
The one hundred m easurem ents were a rra n g e d i n fre q u e n c y c la s s e s
and p l o t t e d on g rap h p a p e r, th e fre q u e n c y c la s s e s fo rm in g th e o r d in a te and
t h e m easurem ents t h e a b s c i s s a .
I t was assumed a t t h i s p o in t t h a t t h e number
o f c a s e s was l a r g e enough f o r v a r i a b i l i t y betw een t h e chromosomes and v a r i a ­
b i l i t y in tro d u c e d by s e c tio n in g t o be d i s t r i b u t e d I n a norm al curve o f e r r o r s .
7.
G ra n tin g th e above a ssu m p tio n , two p o s s ib le ty p e s o f cu rv es
a r e o b ta in a b le .
T h e o r e t i c a l l y , i f t h e two heterochrom osom es a r e a l i k e , a
cu rv e w hich ap p ro x im a te s a norm al d i s t r i b u t i o n curve r e s u l t s .
I f th e y a re
u n l i k e , th e cu rv e may be b im o d al, t h e d if f e r e n c e s betw een th e chromosomes
show ing up i n t h i s m a n n er o v e r and above t h e v a r i a b i l i t y due t o i n d iv id u a l
d if f e r e n c e s and s e c t io n i n g .
P resum ably, th e g r e a t e r th e degree o f d i f f e r ­
ence betw een t h e chromosomes, t h e more d i s t i n c t t h e bim odal a s p e c t o f th e
c u rv e .
T hus, t h i s m ethod e lim in a te d t h e n e c e s s i t y o f i d e n t i f y i n g a g iv en
chromosome I n eac h o f f i f t y p a i r s and le s s e n e d th e chance o f c o n c lu d in g
t h a t chromosomes a r e d i f f e r e n t I n s iz e when a c t u a l l y th e a p p a re n t d i f f e r ­
ence i s due t o s e c t io n i n g .
I n p r a c t i c e , u n f o r t u n a t e ly , t h e cu rv es d id n o t f a l l i n t o two c a te ­
g o r i e s , norm al and b im o d al.
Those s p e c ie s w ith d i s t i n c t d if f e r e n c e s be­
tw een t h e chromosomes gave m ark ed ly bim odal c u rv e s .
On t h e o th e r hand, mono-
m odal c u rv es w hich a r e e x tre m e ly a sy m m e tric a l may r e s u l t from m easurem ents
o f chromosomes w hich a r e o n ly s l i g h t l y d i f f e r e n t i n le n g th *
I n such c a se s
t h e bim o d al c h a r a c t e r o f t h e d a ta i s o b scu red b ecau se t h e modes o f t h e two
c u rv e s a r e so c lo s e t h a t o n ly a s in g le mode a p p e a rs i n a g rap h o f t h e t o t a l
number o f m easu rem en ts.
T hus, t h e ty p e s o f cu rv es a c t u a l l y o b ta in e d ran g ed
from th o s e w hich w ere a p p ro x im a te ly norm al t o th o s e w hich wrere d e f i n i t e l y
b im o d al, w ith an in te r m e d ia te group o f h ig h ly asy m m e tric a l monomodal c u rv e s .
E xcept i n a few i n s t a n c e s , no c o n c lu s io n s could be drawn by in s p e c tio n o f
th e c u rv e s a lo n e .
Any c o n c lu s io n s co n c e rn in g d if f e r e n c e s i n s iz e betw een
chromosomes o f a p a i r , even th o s e o f a v e ry t e n t a t i v e c h a r a c t e r , had t o be
b a se d p r im a r ily upon a m a th e m a tic a l a n a ly s is o f t h e a c t u a l m easurem ents.
S t a t i s t i c a l A n a ly s is o f th e D ata
A.
T reatm en t o f s p e c ie s w ith two heterochrom osom es
The s e l e c t i o n o f an a p p r o p r ia te s t a t i s t i c a l method proved t o be
d iffic u lt.
Common s t a t i s t i c s , su c h a s t , X , and s ta n d a rd e r r o r o f th e d i f ­
f e r e n c e , w hich i n d i c a t e th e p r o b a b i l i t y t h a t two s e t s o f d a ta a r e o r a r e n o t
p a r t o f th e same i n f i n i t e p o p u la tio n , a re u s u a lly employed t o t e s t s i g n i f i ­
cance betw een twro o b serv ed s e t s o f d a ta .
S in ce th e s e c tio n in g f a c t o r made
i t im p o s s ib le t o t e s t t h e m easurem ents o f one h e te r o chromosome a g a in s t th o s e
o f a n o th e r , d i r e c t u se o f t h e above s t a t i s t i c s was p re c lu d e d .
W hile s e c t io n i n g d id n o t in tro d u c e an extrem e v a r i a b i l i t y betw een
heterochrom osom es o f a g iv e n c e l l , t h e same f a c t o r c o n s id e ra b ly in c r e a s e d
t h e v a r i a b i l i t y b etw een m easurem ents from d i f f e r e n t c e l l s .
As a r e s u l t , a
m ethod such a s F i s h e r 's A n a ly s is o f V a ria n c e co u ld n o t be s u c c e s s f u lly em­
p lo y e d .
Because th e m easurem ents had been made from draw ings o f chromosomes
i n a l t e r n a t e s e c t io n s o f c y s t s , and because th e germ c e l l s a r e so sm a ll t h a t
th e l i k e l i h o o d o f a s in g l e chromosome b e in g s e c tio n e d more th a n once i s n o t
l a r g e , D r. S e w a ll W right su g g e ste d w orking w ith r a t i o s betw een t h e p a i r s o f
heterochrom osom es.
1.
T h is m ethod has two a d v a n ta g e s:
I t e n a b le s one t o t r e a t th e p a i r s o f m easurem ents th e m se lv e s
i n s t e a d o f t h e d a ta a s a w hole.
2.
E x p re s s in g t h e d a ta i n th e form o f r a t i o s m inim izes t h e v a r i a ­
b i l i t y betw een p a i r s o f m easurem ents from d i f f e r e n t c e l l s .
I n a l l c a s e s t h e l a r g e s t measurem ent was d iv id e d by th e s m a lle s t.
T h e o r e t i c a l l y t h e r a t i o s may v a ry i n v a lu e from one t o any v a lu e g r e a t e r
th a n one.
I f t h e r a t i o s were grouped i n t o fre q u e n c y c l a s s e s , th e cu rv e ob­
t a i n e d sh o u ld ap p ro x im ate o n e - h a lf o f a norm al c u rv e .
I f th e chromosomes
a r e t h e same s i z e , most o f t h e r a t i o s sh o u ld f a l l i n t o t h e fre q u e n c y c la s s
in c lu d in g th e r a t i o o f one, and c o n s e q u e n tly th e mode o f th e curve sh o u ld
be a t t h i s p o i n t .
On t h e o th e r hand, th e f a r t h e r away from one t h e mode
o c c u r s , th e g r e a t e r t h e d if f e r e n c e s i n s iz e betw een th e chromosomes upon
wrhose m easurem ents t h e r a t i o s a r e b a se d .
S in c e th e m easurem ents o b ta in e d from a l l tw e n ty s p e c ie s f a l l
w ith in 2 .3 8 -4 * 3 0 m i l l i m e t e r s , and th u s do n o t show an extrem e v a r i a b i l i t y ,
and s in c e a r a t i o i s an a b s t r a c t number, i t i s p e r m is s ib le t o compare th e
39
r a t i o s o f one s p e c ie s w ith th o s e o f a n o th e r .
To d e te rm in e w h eth er two d i s ­
t r i b u t i o n s a r e , i n a l l p r o b a b i l i t y , r e p r e s e n t a t i v e sam ples o f a homogeneous
p o p u la tio n , o r w h eth er th e y a r e p ro b a b ly sam ples o f d i f f e r e n t p o p u la tio n s ,
t h e d i f f e r e n c e s betw een t h e s ta n d a rd e r r o r s o f t h e means o f t h e r a t i o s were
c a lc u la te d .
I n each s p e c ie s t h e a r i th m e tic mean o f t h e f i f t y r a t i o s was ob­
t a i n e d u s in g t h e fo rm u la M =
The s ta n d a rd e r r o r o f th e mean was o b ta in e d
th ro u g h t h e u se o f B e s s e l’ s fo rm u la 1
, w hich e n a b le s one t o c a l HN(N - 1)
c u la t e s ta n d a rd e r r o r d i r e c t l y from th e d a ta w ith o u t f i r s t c a l c u l a t i n g th e
s ta n d a rd d e v i a t i o n .
I n t h e s e fo rm u la e , v r e f e r s t o any o f th e f i f t y i n d i ­
v id u a l v a r i a t e s , M t o t h e mean o f t h e r a t i o s and N t o th e t o t a l number o f
m easurem ents.
The s ta n d a rd e r r o r o f th e d if f e r e n c e betw een two means was
d ete rm in e d a c c o rd in g t o t h e o r d in a r y fo rm u la
J
]/ SEj^
p
-
c o rre s p o n d s t o t h e s ta n d a rd e r r o r o f th e f i r s t mean and
seco n d .
2
where SEjj
t o t h a t o f th e
T ab le I shows t h e c a l c u l a ti o n s made f o r one s p e c ie s , P la ty p o e c ilu s
m a c u la tu s .
V alu es ra n g in g from 2 t o 3 tim e s th e s ta n d a rd e r r o r o f th e d i f ­
f e r e n c e a r e c o n s id e re d s i g n i f i c a n t .
I n t h i s i n s ta n c e , t h e e x a c t in f lu e n c e
o f s e c t io n i n g upon t h e mean and e s tim a te d s ta n d a rd e r r o r o f th e p o p u la tio n
was n o t known.
Hence two s e p a r a te sam ples o f 100 m easurem ents were ta k e n
from L e b is te s r e t i c u l a t u s , and th e d if f e r e n c e s betw een t h e s ta n d a rd e r r o r s
o f t h e means o f t h e i r r a t i o s were d e te rm in e d .
The r a t i o o f th e d if f e r e n c e
betw een t h e tw o means o f t h e r a t i o s , t o th e s ta n d a rd e r r o r o f th e d i f f e r ­
ence betw een t h e i r r a t i o s i s 3*17*
Thus f o r t h i s m a t e r ia l th e s a f e s t e s ­
tim a t e o f a s i g n i f i c a n t d if f e r e n c e was c o n s id e re d t o be 3 -5 0 .
was c a l c u l a t e d by t h e u s u a l fo rm u la ;
7
rr .
T / S i f r f - SX&2
S ig n if ic a n c e
A s ig n if ic a n t t e s t in -
40
TABLE I
C a lc u la tio n o f S ta n d a rd E r r o r f o r M easurem ents o f P la ty p o e c ilu s m a c u la tu s
C e ll
Number
R a tio (v )
l a r g e m easurem ent
s m a ll m easurem ent
1
2 .7 5 —1*015
2 .7 1
2 .8 8 - 1 .0 2 9
2 .8 0
2 . 9 8 , 1 .0 7 2
2 .7 8
2 .8 4 „ 1 .0 1 4
2 .8 0
3 .0 2 _ 1 .0 1 0
2 .9 9
3 . 6 3 _ 1 .0 6 1
3.4 2
3 .3 4 _ 1 .0 2 8
3 .2 5
. . ...
3 .0 0 _ I.O 64
2 .8 2
3 .1 7 - 1 . 0 1 3
3 .1 3
. _
3.0 3 _ 1 .0 6 2
2 .8 7
3 . 3O _ 1 .0 8 2
3 .0 5
3 . I 6 - 1 .0 3 3
3.06
3 .4 1 ^ 1 .0 7 9
3.16
3 . 5 4 - 1 .0 2 0
3 .4 7
3 .7 2 _ 1 .0 3 3
3 .6 0
3 .6 4 1 .0 4 0
3 .5 0 '
3 .8 3 _ 1 .0 1 9
3.7 5
_________
3.36 , 1 .0 3 5
3 .4 4
____
3 .1 9 ,1 .0 3 3
3 .0 3
2 .8 6 _ 1 .0 4 0
2 .7 5
3 . 1 9 - 1 .0 2 9
3 .1 0
_ .
3 . 3 1 = 1 .015
3.26
2
3
4
5
6
7
8
9
10
11
12
13
U
15
16
17
IB
19
20
21
22
v - M
(v - M)^
-.0 3 9
.0020
- .0 2 5
.0010
.018
.0003
- .0 4 0
.0020
- .0 4 4
.0020
.0 0 7
-------
-.0 2 6
.0010
.010
.0001
- .0 4 1
.0020
.008
-------
.028
.0010
- .0 2 1
.0004
.025
.0010
—.034
.0010
- .0 2 1
.0004
- .0 1 4
.0002
- .0 3 5
.0010
- .0 1 9
.0004
- .0 0 1
-------
- .0 1 4
.0002
-.0 2 5
.0010
-.0 3 9
.0020
41
R a tio (v )
l a r g e m easurem ent
s m a ll m easurem ent
23
~24
"25
26
"27
28
29
30
31
32
33
34
35
36
37
38
39
2
v - M
(v — M)
3 .2 1 - 1 .0 1 3
- .0 4 1
.0020
3*17
1 .1 1 3
.039
.0030
3 .2 8____________________________________________
3 .7 3 = 1 .0 4 2
- .0 1 2
.0001
1 *5* _______________________________________________
2 . 9 8 , 1 .0 3 8
- .0 1 6
.0003
2 .8 7 _______________________________________________
3 .0 7 = 1 .0 8 4
.030
.0010
2 .8 3_________ _____________________________________
3 .4 9 -1 * 1 2 2
. 068
.0050
3 .1 1_______________________________________________
3 .0 0 = 1 .0 1 0
- .0 4 4
•0020
2 .9 7
3 .2 4 _ 1 .0 9 8
.044
.0020
2 .9 5 _____________________________________________
3 .4 0 -,1 .0 1 8
-.0 3 6
.0010
3 .3 4 _______________________________________________
2 . 5 7 - 1 .0 2 4
- .0 3 0
.0010
2 .5 1_______________________________________________
3*52 =1 .1 1 0
.056
.0030
3-1.1 ?______________________________________________________
3 .2 9 ^ 1*2.05
.151
.0230
2 . 73
3 .1 1 . 1 .0 6 3
.009
-----2 . 8 3_______________________________________________
3 .1 4 - 1 .0 0 6
- .0 4 8
.0020
3 .1 2_______________________________________________
3.2 5 = 1.0 5 5
.001
-----3 .0 8____________________ __________________________
3 . 5 7 ^ 1.0 6 5
.011
.0001
3 .^ 3_______________________________________________
3 .2 4 = 1 .0 2 2
- .0 3 2
.0010
- l i l ? ______________________________________________________
40
41
42
43
3 .1 1 _1.054
.000
------2.95 ' _____________________________________________
3*62 ,1 .0 6 5
.011
.0001
3 .4 0 _______________________________________________
3 .5 1 - 1 .3 1 0
.256
.0660
2 .6 8
2 .4 1 _ 1 .0 0 7
- .0 4 7
.0020
2 . 3.9 ~____________________________________________________
3 .2 2 - 1 .0 1 5
- .0 3 9
.0020
_____________________________________________________
3 .5 0 = 1 .0 9 4
.040
.0020
3*2.0______________________________________________
42
C e ll
Number
R a tio (v )
l a r g e m easurem ent
s m a ll m easurem ent
3 .0 4 = 1 .0 2 0
2 .9 8
3 . 2.4 _ 1 .0 8 4
2 .9 9
3*30 = 1 .0 3 4
3 .1 9
2 .9 7 __1 .0 2 8
2 .8 9 "
2 .4 8 ^.1.074
2 .3 1
46
47
48
49
50
T o ta ls
N
=
=
5&S.712
s
.0010
.030
.0010
- .0 2 0
.0004
- .0 2 6
.0010
.020
.0004
.1214
1 .0 5 4
50
T s~ 7 v - M)2
I N (N - 1)
-
f o .!2 L T =
I 2450
(v - M) 2
- .0 3 4
52.719
M = &
S^j
v —M
0.00703
d i c a t e s t h a t d i f f e r e n c e s betw een t h e means o f two sam ples p ic k e d a t random
from a homogeneous p o p u la tio n c o u ld n o t exceed 3 .5 tim e s th e sq u a re r o o t o f
t h e s ta n d a r d e r r o r o f t h e d i f f e r e n c e betw een th e two m eans.
Each s p e c ie s was t e s t e d w ith th e n in e te e n o th e r s p e c ie s and th e
number o f s i g n i f i c a n t t e s t s p e r s p e c ie s was c o u n te d .
S p e c ie s were a rra n g e d
i n l i n e a r o r d e r , b e g in n in g w ith t h e one showing t h e g r e a t e s t number o f s i g ­
n ific a n t t e s t s .
T h is arran g em en t o f d a ta co u ld be g r a p h ic a lly e x p re ss e d
and f o r p u rp o se s o f s tu d y and com parison i t pro v ed t o be a co n v en ien t method
o f h a n d lin g t h e m a t e r i a l .
T reatm en t o f s p e c ie s w ith t h r e e h et e ro c h r omos ome s
F o r tu n a te ly , i n t h e s p e c ie s w ith more th a n two heterochrom osom es,
th e chromosomes fo rm in g a c o h e re n t group move to w ard one p o le o f th e s p in d le
and can be d is t i n g u i s h e d from t h e s in g le chromosome g o in g t o t h e o p p o s ite
p o le .
I n each c e l l t h e m easurem ents o f t h e s in g le chromosome “were com­
p a re d t o t h e mean o f t h e m easurem ents o f th e group o f chromosomes.
F or each
o f t h e f i f t y c e l l s i n any g iv e n s p e c ie s , t h e d if f e r e n c e betw een th e s in g le
m easurem ent and t h e mean o f t h e m easurem ents o f th e m u ltip le chromosomes
were d e te rm in e d .
The mean o f th e s e d if f e r e n c e s betw een t h e chromosomes i n
f i f t y c e l l s was s u b tr a c te d from each o f t h e f i f t y d i f f e r e n c e s and th e r e s u l t
s q u a re d .
The sum o f t h e s e sq u a re s was u sed t o d e term in e th e s ta n d a rd e r r o r
o f th e d i f f e r e n c e a c c o rd in g t o t h e fo rm u la
] £l(d - d )^ . i n w hich d i s th e
> N(N - 1)
d i f f e r e n c e , d t h e mean o f t h e d i f f e r e n c e s , and N th e number o f c e l l s i n w hich
chromosomes w ere m easured.
H aving o b ta in e d t h e s ta n d a rd e r r o r o f th e mean d if f e r e n c e (S E ^),
t h e s t a t i s t i c t can be d e te rm in e d th ro u g h t h e u se o f t h e fo rm u la t = —S - .
SEd
I n s p e c t i o n o f t h e fo rm u la f o r t and com parison o f i t w ith t h e form ula f o r
s ig n i f i c a n c e , d e s c r ib e d i n t h e p r e c e d in g s e c t io n , shows them t o be s i m i l a r .
S ig n if ic a n c e t e s t s f o r s m a ll sam ples a r e o f te n e s tim a te d on th e b a s is o f
t i n s t e a d o f upon a r a t i o o f d i f f e r e n c e s betw een tw o means t o t h e s ta n d a rd
e r ro r o f th e d iffe re n c e .
However, s in c e chromosomes A and B co u ld n o t be
d is tin g u i s h e d from c e l l t o c e l l , t h e t - t e s t c o u ld n o t be u sed when o n ly
tw o heterochrom osom es w ere o b s e rv e d .
The s t a t i s t i c t i s a n in d e x o f th e
p r o b a b i l i t y t h a t t h e v a lu e s t e s t e d would a p p e a r by chance i n random sam­
p lin g .
A v a lu e o f t c o rre s p o n d in g t o a p r o b a b i l i t y o f 0 .0 1 means t h a t
t h e r e i s o n ly one chance out o f 100 t h a t t h e d if f e r e n c e s betw een t h e mea­
su rem en ts o f t h e s i n g l e chromosome and t h e mean o f t h e group o f chromosomes
c o u ld have a r i s e n by ch an ce.
T a b le I I (page 45) shows t h e c a l c u l a t i o n s f o r
G -irard in u s met a l i i c u s
When t h e r e w ere o n ly two chromosomes co m p risin g t h e group g o in g
t o one p o le o f t h e c e l l d u rin g t h e p rim a ry sp e rm a to c y te d i v i s i o n , t h e p a i r s
o f m easurem ents f o r t h e s e chromosomes were t r e a t e d by th e same m ethod u sed
f o r th o s e s p e c ie s w ith o n ly two heterochrom osom es.
Thus two s e t s o f s t a ­
t i s t i c s were c a l c u l a t e d , one e s tim a tin g d if f e r e n c e s betw een th e odd chromo­
some and th o s e a s s o c i a t e d i n a g ro u p , and t h e o th e r e s tim a tin g d i f f e r e n c e s
betw een t h e chromosomes fo rm in g t h e g roup.
C.
T re atm en t o f s p e c ie s w ith f o u r heterochrom osom es
I n one s p e c i e s , f o u r heterochrom osom es w ere o b se rv e d , one chromo­
some g o in g t o one p o le and t h e o th e r t h r e e t o t h e o p p o s ite p o le .
As i n t h e
s p e c ie s w ith t h r e e heterochrom osom es, t h e measurem ent o f t h e s in g le chromo-
45
TABLE I I
C a lc u la tio n o f t f o r G ira rd in u s met a l i i cus
C e ll
Number
A
1
3 .3 4
2
3 .4 5
2 .8 2
- -3
4
3.6 6
5
3 .1 7
6
4.29__
7
4 .5 3
8
4 .7 1
9
. A*55
10
. 3 .9 3
11
3 .6 4
12
3 .7 7
3 .2 2
13
14
. 4 .3 3
15
4 .5 1
16
3 .5 9
17
3 .7 9
18
3 .8 2
19
3 .2 7
20
5 .5 7
21
3 .3 4
22
3 .5 1
3 .3 3
23
24
4 .2 4
3 .0 8
25
26
3 .5 4
27
3 .4 9
28
3 .4 9
2 .9 9
. 29
3 .2 2
30
3 .9 3
31
32
3 .1 5
3*57
__ 13
2 .9 1
__ 3 4 _____
3 .0 6
3 5 ____
36
3 .5 1
5 .1 7
,.3.7_..
38
3 .3 4
3 .1 0
39
3 .8 1
40
41
3 .3 5
42
3.59__
3.26
43
3
.6 1
44
BfcC
2
, (A-BtC
d"
2
d -d
0 .0 8
- 0 .1 7 8
3 .2 6
0 .0 5 2
0 .3 1
3 .1 4
2 .6 8
-0 .1 1 8
0 .1 4
3 .0 0
0.4 0 2
0 .6 6
- 1 .6 2
-1 .3 6
4 .5 3
2 .8 7
1 .1 6
1 .4 2
0 .5 1 2
3-76
. 0 .7 7
1 .4 8
1 .2 2
_ _ 3 .2 3
2 .8 8
1 .6 7
1 .4 1
0 .2 7 2
3*40
0 .5 3
0
.3 3 2
3 .0 5
0 .5 9
0
.0
32
3 .4 8
0.2.9
- 0 .3 2
- 0 .5 7 8
3 .5 4
0 .922
1 .1 8
3 .6 5
1 .2 8
1 .0 2
3 .2 3
0 .2 4 2
0 .3 0
3 .0 9
3 .4 0
0 .1 3 2
_ . 0 .3 9 .
3 .2 1
0 .6 1
0 .3 5 2
- 0 .1 2
-0 .3 7 8
3 .3 9
3 .1 8
2 .1 3
2 .3 9
3.0 2
0 .8 2
0 .5 6 2
0 .3 2
0 .0 6 2
3 .1 9
0 .1 5 2
2 .9 7
0 .4 1
4 .1 2
0 .1 2
- 0 .1 3 8
- 0 .9 4 8
-0 .6 9
3 .7 7
0 .0 1 2
0
.2
7
.
3 .2 7
0
.0 8 2
3.15
0 .3 4
3 .3 2
0 .1 7
- 0 .0 8 8
4*66
- 1 .6 7
___ -1*93
. - 0 .1 7
- 0 .4 2 8
3 .3 9
3.56
0.1 1 2
0 .3 7
0 .2 0 2
0 .4 6
2 .6 9
3 .6 2
- 0 .3 0 8
-0 .0 5
3 .2 2
-0 .5 6 8
_____ - 0 .3 1
-0 .5 8 8
__.__2.12 __ ....... - 0 .3 3
-0 .2 6
-0 .5 1 8
3 .7 7
1.26
1 .0 0
3 .9 1
-0 .6 6 8
3.75
-0 .4 1
- 0 .3 9 8
3 .2 4
- 0 .1 4
0.06
- 0 .1 9 8
3.7 5
- 0 .5 2
- 0 .7 7 8
3 .8 7
- 0 .1 0 8
0.15
3*44
0
.0
8
- 0 .3 3 8
3 .3 4
0 .042
0
.3
0
, .3* 3.1____
_
(d -d )2
0 .0 3 2
0 .0 0 3
0 .0 1 4
0 .1 6 2
2 .6 2 4
1*135
0.2 6 2
1 .4 8 8
1.9 8 8
0 .0 7 4
0 .1 1 0
0 .0 0 1
0 .3 3 4
0 .8 5 0
1 .0 4 0
0 .0 5 9
0 .0 1 7
0 .1 2 4
0 .1 4 3
4 .5 3 7
0.316
0 .0 0 4
0 .0 2 3
0.019
0 .8 9 9
0 .0 0 0
0 .0 0 7
0 .0 0 8
3.725
0 .1 8 3
0 .0 1 3
0 .0 4 1
0 .095
0 .3 2 3
0 .3 4 6
0 .2 6 8
1 .0 0 0
0.446
0 .1 5 8
0 .039
0 .6 0 5
0 .0 1 2
0 .1 1 4
0 .0 0 2
C e ll
Number
Bj-C
2
A
45 _
46
47
43
49
50 . . .
_
_
, A-BfC
d=
2
. _1._6_5 .
. 3 .4 2 _
3.5 6
3-21 ........
3 *44
3.2 5
3 .8 9
2 .3 4
3 .0 7
3 .3 2
3 .6 3
_3*59
0 .2 4
- 0 .4 2
- 0 .4 9
0 .1 1
0 .1 9
0 .3 4
T -2 0 .2 2
- 7*34
- 1 2 .3 3
d
se5
t
zd
50
=
=:
=
=
1 2 .3 3
50
V ^ C d -d )2
1 N (N -l)
d
SE^
=
0 .2 5 3
0 .0 9 1
=
=
=
0 .0 0 0
0 .4 6 0
0 .5 6 0
0 .0 2 2
0 .0 0 5
0 .0 0 7
2 0 .7 9 7
0 .0 9 1
2 .3 0
F or 49 d e g re e s o f Freedom, t a t ±% p o in t = 2 .6 3 0 .
o f d a ta i s s i g n i f i c a n t .
-0 .0 1 8
-0 .6 7 8
-0 .7 4 8
-0 .1 4 8
-0 .0 6 8
0 .0 8 2
(d -d )2
0 .2 5 8
| 2 0 .7 9 7
) 2450
=
d -d
T h e re fo re t v a lu e
some was compared w ith t h e mean o f t h e g ro u p , and t h e s t a t i s t i c t c a l c u l a t e d .
To compare t h e chromosomes i n t h e g ro u p , r a t i o s betw een th e t h r e e
chromosomes a , b , an d c w ere d e te rm in e d .
I n each o f t h e 50 c e l l s , th e
chromosome w ith t h e l a r g e s t m easurem ent was d e s ig n a te d as a , and i t s mea­
surem ent d iv id e d b y t h e m easurem ents o f chromosomes b and c .
The m easure­
m ents o f b and c w ere e x p re ss e d a s a r a t i o by d iv id in g b by c o r c by b
dep en d in g upon w hich chromosome had th e l a r g e r m easurem ent.
t h e mean o f t h e t h r e e r e s u l t i n g r a t i o s was o b ta in e d .
I n each c e l l
T hese f i f t y mean
r a t i o s w ere t r e a t e d l i k e t h e r a t i o s betw een s in g l e p a i r s o f heterochrom o­
somes •
IV .
RESULTS OF CYT0L0GICAL STUDY AND STATISTICAL ANALYSIS OF
THE HETEROCHROMOSOMES OF TWENTY SPECIES OF POECILIIDAE
S p e c ie s w ith Two Heterochromosom es
A.
I n tr o d u c t i o n
T h e re i s no doubt t h a t a l l o f t h e s p e c ie s o f P o e c i l i i d a e s tu d ie d
p o s s e s s tw o o r more heterochrom osom es, w hich may be d is tin g u is h e d from t h e
re m a in d e r o f t h e chromosomes by means o f t h e i r p e c u l i a r b e h a v io r.
W hile
a l l heterochrom osom es a r e n o t se x chromosomes, i t i s e n t i r e l y j u s t i f i a b l e
t o c o n s id e r s e x chromosomes a s a s p e c i a liz e d ty p e o f heterochrom osom e.
G e n e tic a l s tu d i e s upon t h e p o e c i l i i d f i s h e s have shown c e r t a i n c h a r a c te r s
t o have a s e x - lin k e d i n h e r i t a n c e and th e r e f o r e su g g e st t h a t t h e s e t e l e o s t s
may have c y t o l o g i c a l l y d is t i n g u i s h a b le se x chromosomes.
C o n seq u en tly , I t i s
im p o rta n t t o compare t h e b e h a v io r o f th e heterochrom osom es p r e s e n t i n th e
p rim a ry sp e rm a to c y te d i v i s i o n s w ith th e b e h a v io r o f chromosomes w hich have
been d e f i n i t e l y e s ta b li s h e d as s e x d e te rm in in g .
F or th e sak e o f c l a r i t y ,
i t may be w e ll t o d ig r e s s a t t h i s p o in t lo n g enough t o d is c u s s th o s e c h a ra c ­
t e r i s t i c s o f s e x chromosomes w hich a r e o f s u f f i c i e n t l y g e n e r a l c h a r a c te r t o
be u se d a s c r i t e r i a .
1.
D u rin g t h e gro w th p e rio d o f t h e p rim a ry sp e rm a to c y te s th e se x
chromosomes become h e te r o p y c n o tic , a p p e a rin g a s a homogeneous, i n t e n s e l y
s t a i n i n g ch ro m o so m e-n u cleo lu s.
and s t a i n w ith b a s ic d y e s.
They become s p h e r i c a l , g r e a t l y condensed,
The au tosom es, d u rin g t h i s same p e r io d , te n d t o
be t h r e a d - l i k e , and l i g h t l y s t a i n i n g .
H e te ro p y c n o sis i s v e ry c h a r a c t e r i s t i c
o f th e se x chromosomes a lth o u g h t h e r e i s c o n s id e ra b le v a r i a t i o n i n r e s p e c t
t o th e tim e a t v/hich i t o c c u rs and i n th e d eg ree o f c o n d e n s a tio n .
I n some
a n im a ls , su ch a s A phis s a l i c e t i , t h e p ro c e ss i s o m itte d .
2.
W hile a plasmosome i s n o t commonly p r e s e n t d u rin g t h e e a r l y
p a r t o f t h e g ro w th p e r io d , i t a p p e a rs to w ard th e m iddle o f t h i s p e r io d , o f te n
becom ing a s s o c i a t e d w ith t h e chrom osom e-nucleolus ( h e te ro p y c n o tic se x chromo­
somes) t o form a t r u e a m p h in u c le o lu s .
L a te r th e am p h in u cleo lu s b re a k s up
i n t o i t s component p a r t s .
3.
Sex chromosomes, w h eth er o f th e XX - XO, XX - XY o r ZZ - ZW
ty p e , show t h e same g e n e r a l b e h a v io r d u rin g t h e m e io tic d i v i s i o n s .
They
d iv id e e q u a t i o n a l l y i n one d i v i s i o n and i n t h e o th e r p a s s u n d iv id e d t o th e
p o le s .
The d i f f e r e n t i a l d i v i s i o n o r h e te r o k in e s is ( i . e . , t h a t i n w hich th e
sex chromosomes p a s s u n d iv id e d t o o p p o s ite p o le s ) may t a k e p la c e I n e i t h e r
t h e f i r s t o r second sp e rm a to c y te d iv i s i o n .
4..
D u rin g h e te r o k in e s is t h e sex chromosomes may p re c e d e th e a u to ­
somes t o t h e p o le s ( p re c e s s io n ) o r l a g b eh in d them ( s u c c e s s io n ) .
5.
I n a g r e a t many c a s e s , d u rin g th e f i r s t sp erm ato cy te d i v i s i o n ,
th e p o s i t i o n o f t h e se x chromosomes i n r e s p e c t t o t h e e q u a to r ia l p l a t e i s
alm o st c o n s ta n t.
As a g e n e r a l r u l e , t h e se x chromosomes l i e a s h o rt d is ta n c e
away from t h e autosom es m assed' upon t h e e q u a t o r i a l p l a t e .
6.
U s u a lly by t h e tim e o f t h e p rim a ry sp e rm a to c y te d iv i s i o n t h e
se x chromosomes become d o u b le , owing t o th e ap p earan ce o f a l o n g itu d in a l
s p l i t , w hich r e p r e s e n t s t h e p la n e o f t h e e q u a tio n a l d i v i s i o n .
D uring th e
p rim a ry sp e rm a to c y te d i v i s i o n t h e se x chromosomes p a s s t o t h e p o le s a s lo n ­
g i t u d i n a l l y dou b le b o d ie s , p ro v id e d t h a t th e h e t e r o k i n e t i c d i v i s io n ta k e s
p la c e a t t h i s tim e .
7.
I n a n im a ls e x h i b i t i n g t h e XX - XY ty p e o f s e x d e te r m in a tio n ,
t h e X-chromosome i s alm o st alw ays l a r g e r th a n th e Y.
A ccording t o W ilson
(1928, p . 768), among th e H em iptera, C o le o p te ra and D ipt e r a , a l l g r a d a tio n s
i n s i z e r e l a t i o n s h i p s betw een t h e X and Y may be o b se rv e d , f o r i n some s p e c ie s
Y may be s m a lle r t h a n , and I n o th e r s e q u a l t o X I n r e s p e c t t o s i z e .
A ccord­
in g t o D a rlin g to n (1937* P- 3 5 8 ), c a s e s w hich show Y t o be much s m a lle r th a n
X w ere fo u n d by M etz and Nonidez i n A s ilu s not a t us and by Agar i n th e mar­
s u p ia l M acropus.
Any heterochrom osom e w hich f u n c tio n s a s a se x chromosome may show
a l l o r p a r t o f t h i s c h a r a c t e r i s t i c b e h a v io r.
However, i n a g iv e n s p e c ie s
some p h a se s o f such b e h a v io r may n o t be o b se rv e d .
B.
C y to lo g ic a l O b s e rv a tio n s
F i f t e e n o f t h e tw e n ty s p e c ie s o f P o e c il iid a e s tu d ie d p o s s e s s e d
one p a i r o f heterochrom osom es.
R e se a rc h o f Dr. E. M. R a ls to n upon P l a t y -
p o e c ilu s m a c u la tu s , X iphophorus h e l l e r i i , and th e h y b rid betw een th e s e two
s p e c i e s , i n d i c a t e s t h a t t h e s ta g e o f m e io s is i n w hich t h e y a r e most con­
s p ic u o u s i s t h e p rim a ry sp e rm a to cy te d i v i s i o n .
S in c e , i n th e p r e s e n t s tu d y ,
i n t e r e s t has been c e n te r e d upon th e f u l l y form ed heterochrom osom es and t h e i r
b e h a v io r , t h e p rim a ry sp e rm a to c y te d i v i s i o n was b e lie v e d b e s t f o r s tu d y .
A ll o f t h e chromosomes s t a i n v e ry i n t e n s e l y d u rin g t h i s d i v i s i o n , so t h a t
s l i d e s had t o be c o n s id e r a b ly d e s ta in e d i n o r d e r t o make t h e chromosomes
s ta n d out s h a r p ly from one a n o th e r a g a in s t t h e i r c y to p la sm ic background.
U n f o r tu n a te ly , m ost o f t h e s ta g e s d u rin g th e grow th p e r io d o f th e p rim a ry
s p e rm a to c y te s w ere t o o much d e s ta in e d t o s tu d y w ith any d eg ree o f th o ro u g h ­
n e s s , so t h a t t h e b e h a v io r o f t h e heterochrom osom es d u rin g t h i s p e r io d i s
m e re ly t e n t a t i v e l y o u t l i n e d .
1.
P seu d o x ip h o p h o ru s b im a c u la tu s
B ecause i n a l l o f t h e f i f t e e n s p e c ie s o f P o e c i l i i d a e p o s s e s s in g
one p a i r o f heterochrom osom es, t h e b e h a v io r o f t h i s p a i r i s v e r y s i m i l a r ,
P seu d o x lp h o p h o ru s b im a c u la tu s has been s e le c t e d f o r th e ty p e form upon w hich
a g e n e r a l d e s c r i p t i o n o f chromosome b e h a v io r w i l l be b a s e d .
F o llo w in g t h e
g e n e r a l a c c o u n t, t h e re m a in in g f o u r te e n s p e c ie s w i l l be d is c u s s e d b r i e f l y ,
s t r e s s i n g any v a r i a t i o n s from t h e ty p e form .
T h ere i s some i n d i c a t i o n i n Pseudoxlphophorus t h a t t h e h e te r o ­
chromosomes may become h e te r o p y c n o tic d u rin g th e grow th p e r io d .
T here a p p e a r
t o be two i n t e n s e l y s t a i n i n g compact b o d ie s lo c a te d i n t h e n u c le u s d u rin g
t h e le p t o t e n e and s y n a p to te n e s ta g e s .
o n ly one su ch body i s n o t i c e a b l e .
B eg in n in g about th e p ach y ten e s ta g e ,
T h is body i s a l s o d e e p ly s t a i n i n g and
compact b u t a p p e a rs t o be d u m b -b ell shaped and d e c id e d ly d o u b le .
I t i s p o s­
s i b l e t h a t w ith a p p r o p r i a t e l y s ta in e d m a te r ia l and w ith more s tu d y i t can
be shown t h a t t h e s e b o d ie s a r e chromosome n u c le o li ( s e x chromosomes) u n d er­
g o in g a p ro c e s s o f h e te r o p y c n o s is .
I t seems t o be q u ite c e r t a i n t h a t i f th e
p r o c e s s o f h e te ro p y c n o s is does o c c u r i n P seu d o x lp h o p h o ru s, i t i s not o f t h e
extrem e ty p e c h a r a c te r iz e d by com plete i s o l a t i o n o f th e chromosomes w ith in
j a s e p a ra te v e s ic le .
I n t h i s s p e c ie s no v e s i c l e was o b serv ed and, w h ile
t h e r e seemed t o be a g e n e r a l te n d e n c y f o r th e ’’n u c le o lu s 1' t o become more o r
l e s s i s o l a t e d a t t h e edge o f t h e n u c le u s , t h i s d id n o t seem t o be an i n —
J
j v a r i a b l e c o n d itio n .
;
I n some a n im a ls , a lo n g to w ard th e m id d le o f th e grow th p e r io d , th e
| se x chromosomes become a s s o c i a t e d w ith t h e plasm osom e.
W hether o r not such
| an a s s o c i a t i o n e x i s t s i n P seud o x iphophorus i s unknown.
B efore any c o n c lu -
| s io n s c o u ld be draw n, i t would be n e c e s s a ry t o u se an a c id o p h i lic c o u n te r s t a i n , su ch a s e o s in , i n o r d e r t o d i f f e r e n t i a t e th e plasmosom e, p ro v id e d ,
I o f c o u r s e , t h a t one i s p r e s e n t .
I
F o llo w in g t h e p a ch y ten e s ta g e t h e b iv a le n t th r e a d s become v e ry
d i f f u s e and l i g h t l y s t a i n i n g .
T h is d i f f u s e s ta g e may r e p r e s e n t t h e p ro p h ase
; o f t h e p rim a ry sp e rm a to c y te d i v i s i o n .
At l e a s t th e t e t r a d s o f t h i s d iv i s i o n
seem t o a r i s e from c o n d e n s a tio n o f t h e l i g h t l y s t a i n i n g t h r e a d s .
E a r ly t e -
; t r a d s a r e more o r l e s s i r r e g u l a r i n shape and condense r a p i d ly t o form t h e
t y p i c a l s p h e r i c a l o r ro d -s h a p e d chromosomes o f t h e p rim a ry sp e rm a to c y te d i ­
v is io n .
I n t h i s d i v i s i o n th e s e become so m assed upon t h e e q u a t o r i a l p l a t e
t h a t I t i s im p o s s ib le t o d i s t i n g u i s h th e o u t lin e s o f any i n d iv id u a l chromo­
some ( F ig s . 1 , 38, 51* 73)*
However, t h e r e i s one p a r t i c u l a r p a i r o f chromo­
somes w hich behaves so d i f f e r e n t l y from t h e o th e r s t h a t i t seems e n t i r e l y
j u s t i f i a b l e t o c o n s id e r them as h et ero chromosome s .
The two chromosomes com­
p r i s i n g t h i s p a i r a r e so c l o s e ly a s s o c ia te d t h a t t h e y a p p e a r as a l a r g e b i ­
v a le n t chromosome o f somewhat r e c ta n g u la r sh ap e.
T h is "chromosome” la g s
when a p p ro a c h in g t h e m etaphase p l a t e so t h a t , even a f t e r t h e r e s t o f th e
chromosomes have become a rra n g e d upon th e s p in d le , i t may be o b serv ed some
d is t a n c e away from t h e s p in d le .
I t seems t o be co n n ected t o t h e au to so m al
group by means o f a s p in d le f i b e r ( F ig . 1 ) .
B e fo re t h o s e chromosomes upon t h e e q u a t o r i a l p l a t e have d iv id e d ,
t h e p a i r e d heterochrom osom es s e p a r a te ( F ig . 3 8 ) .
They a r e s t i l l i s o l a t e d
from t h e chromosomes a rra n g e d upon t h e s p in d le and i n fa v o ra b le s e c tio n s
ea c h one may be o b se rv e d a tta c h e d t o t h e s p in d le by a f in e t r a n s l u c e n t f i b e r .
O b s e rv a tio n s o f a l a r g e number o f c e l l s le a d one t o conclude t h a t th e p o s i­
t i o n o f t h e heterochrom osom es a t t h i s tim e I s q u i t e c o n s ta n t and i n a m ajo r­
i t y o f t h e s e c t io n s one a p p e a rs l a r g e r th a n t h e o th e r,.
The l a r g e r chromosome
i s i n t h e form o f an e lo n g a te o v a l, in te r m e d ia te i n shape betw een a s p h e r i c a l
chromosome and a ro d -s h a p e d one.
s p h e ric a l.
The s m a lle r o f t h e two te n d s t o be more
The heterochrom osom es do n o t a p p e a r t o have m edian c o n s t r i c t i o n s .
S h o r tly a f t e r s e p a r a t i o n , t h e heterochrom osom es a r e drawn upon t h e m etaphase
p l a t e and p ro c e e d t o o p p o s ite p o le s o f th e s p in d le , p r a c t i c a l l y re a c h in g t h e
p o le s b e f o r e t h e r e s t o f t h e chromosomes d iv id e ( F ig . 51)*
T h e re f o re , i n
P seu d o x lp h o p h o ru s t h e h e t e r o k i n e t ic d iv i s i o n ta k e s p la c e b e fo re th e eq u atio n a l.
I n t h i s s p e c i e s , th e n , t h e h e t e ro chromosomes a r e c h a r a c te r iz e d by
a d e la y i n a p p ro a c h in g t h e m etaphase p l a t e , a p re c o c io u s d i v i s io n I n m eta­
p h a se and an an ap h ase w hich I s so p re c o c io u s t h a t w h ile th e y p re c e d e t h e
o th e r s t o t h e p o l e s , t h e p r e c e s s io n i s so advanced t h a t th e s e chromosomes
have re a c h e d th e p o le s b e f o re th o s e upon t h e p l a t e have d iv id e d .
The d u r a tio n o f t h e m etaphase s ta g e o f t h e p rim a ry d i v i s i o n i s
r e l a t i v e l y lo n g , f o r p r a c t i c a l l y t h r e e - f o u r t h s o f t h e t e s t i c u l a r c y s ts con­
t a i n i n g c e l l s i n t h e p rim a ry d i v i s i o n show them t o be I n m etap h ase.
Just
p r i o r t o d i v i s i o n t h e autosom es seem t o r e p e l one a n o th e r f o r t h e y tem por­
a r i l y s p re a d o u t upon t h e s p in d l e .
B ecause o f t h i s b e h a v io r, p o la r view s
o f t h i s b r i e f s ta g e a r e ad m ira b le f o r m aking chromosomal c o u n ts .
D uring
t h i s p e r io d t h e heterochrom osom es a r e i n advanced anaphase so t h a t i n p o la r
v iew s s e c tio n e d p a r a l l e l t o th e l o n g i t u d i n a l a x is o f t h e s p in d le th e y may
be o b se rv e d a s i s o l a t e d b o d ie s a tta c h e d t o th e c e n t r a l group by a s p in d le
f i b e r ( F ig . 73) •
U n lik e m e ta p h a se , an ap h ase ta k e s p la c e v e r y r a p id ly .
th e c e l l s o b s e rv e d , o n ly ab o u t f i f t y a n ap h ases were o b se rv e d .
In a l l of
I n th e s e th e
autosom es had re a c h e d t h e p o le s so t h a t t h e heterochrom osom es co u ld no lo n g e r
be d i s t i n g u i s h e d .
I n t h e se c o n d a ry sp e rm a to c y te d i v i s i o n , t h e heterochrom osom es
p ro b a b ly d iv id e e q u a t i o n a l l y .
They e v id e n tly d iv id e a t th e same tim e a s
t h e autosom es f o r th e y were n o t o b serv ed i s o l a t e d from t h e g e n e r a l group
now w ere th e y o b serv ed p re c e d in g t h e autosom es t o t h e p o le s f o llo w in g a
p re c o c io u s m etap h ase and an a p h a se .
2.
L e b is te s r e t i c u l a t u s
The b e h a v io r o f th e heterochrom osom es i n L e b is te s fo llo w s th o s e
o f P seu d o x lp h o p h o ru s,
T here a r e , however, d if f e r e n c e s i n m orphology b e­
tw een t h e h e t e ro chromosomes o f t h e two s p e c ie s .
p a i r i s m ark ed ly l a r g e r th a n i t s p a r t n e r .
I n L e b is te s one o f th e
C o n seq u en tly th e two members
o f t h i s p a i r a r e r a r e l y s e c tio n e d so t h a t th e y a p p e a r t o be o f e q u a l s iz e
i n a g iv e n c e l l .
A second p o in t o f d if f e r e n c e i s t h a t b o th th e lo n g and
t h e s h o r t chromosomes have a c h a r a c t e r i s t i c d u m b -b e ll-lik e form , due t o th e
p re s e n c e o f a m edian c o n s t r i c t i o n ( F ig s . 2 , 37* 52, 74)*
These c o n s tr i c ­
t i o n s may i n d i c a t e t h e p la n e o f t h e e q u a tio n a l d iv is i o n o r th e y may be
s t r u c t u r a l c h a r a c t e r i s t i c s o f t h e chromosomes th e m s e lv e s .
S in ce th e s e
chromosomes can n o t be d is ti n g u i s h e d from t h e autosom es i n th e seco n d ary
sp e rm a to c y te d i v i s i o n , no c o n c lu s io n c o n c e rn in g a p o s s ib le f u n c tio n a l s i g -
n if i c a n c e o f t h e s e c o n s t r i c t i o n s co u ld be re a c h e d .
3*
L in d a n i g r o f a s c i a t a
I n t h i s s p e c ie s t h e b e h a v io r and m orphology o f th e h et e ro chromo­
somes e x a c t l y p a r a l l e l s t h a t o f P se u d o x lp h o p h o ru s.
The chromosomes a p p ear
t o be o f d i f f e r e n t s i z e i n a g r e a t many c e l l s b u t t h e s iz e d i f f e r e n c e i s
n o t a s o b v io u s a s t h a t o b serv ed i n P se u d o x lp h o p h o ru s.
T here a r e more c e l l s
i n w hich t h e y a p p e a r t o be o f t h e same s iz e th a n i n th e ty p e s p e c ie s .
As
a g e n e r a l r u l e , t h e s l i g h t e r t h e d if f e r e n c e betw een th e chromosomes i n
r e s p e c t t o s i z e , t h e g r e a t e r t h e chance f o r s e c tio n in g t o make them a p p ear
t o be a l i k e ( F ig s . 3 , 36, 53, 7 5 ).
4*
Het e r a n d r i a form osa
B eh a v io r o f t h e h e t e ro chromosomes i n H e te ra n d ria fo llo w s t h a t o f
t h e ty p e form ( F ig s . 4* 35* 54* 7 6 ).
The heterochrom osom es i n t h i s s p e c ie s
a r e r o d - l i k e b u t b e ca u se o f s l i g h t m edian tr a n s v e r s e c o n s tr i c t i o n s ap p ear
more o r l e s s d u m b -b e ll-sh a p e d .
The germ c e l l s i n H e te ra n d ria a r e much
s m a lle r t h a n t h o s e i n any o f t h e n in e te e n o th e r s p e c ie s .
S econdary s p e r­
m a to c y te n u c l e i a r e e x tre m e ly s m a ll w h ile th o s e o f th e p rim ary sperm ato­
c y te a r e ab o u t t h e same s i z e a s t h e seco n d ary sp e rm ato cy te n u c l e i o b serv ed
i n t h e o th e r s p e c i e s .
A d e f i n i t e c o n c lu s io n r e g a rd in g t h e s iz e r e l a t i o n ­
s h ip betw een t h e two heterochrom osom es co u ld not be drawn.
5.
As f a r a s c o u ld be o b s e rv e d , th e h e t ero chromosomes o f t h e fo llo w ­
i n g f o u r s p e c ie s behaved l i k e th o s e o f P seudoxlphophorus.
However, i n
t h e s e s p e c ie s i t p ro v ed d i f f i c u l t t o d e c id e , on t h e b a s is o f o p t i c a l e v i­
dence a lo n e , w h e th e r o r n o t t h e r e was a d if f e r e n c e i n s iz e betw een th e
h e t e ro chromosome s .
T h is o f c o u rse was not th e c a se i n P seu d o x lp h o p h o ru s.
The chromosomes o f t h e s e f o u r s p e c ie s were not l i k e th o s e o f P seu d o x ip h o -
p h o ru s b u t w ere more l i k e th o s e o f L e b is te s and H e te r a n d ria b ecau se t h e
p re s e n c e o f c o n s t r i c t i o n s gave them t h e c h a r a c t e r i s t i c d u m b -b ell shape o f
th e s e l a t t e r tw o fo rm s.
a*
Q u in ta n a a t r iz o n a
b.
X iphophorus h e l l e r i i
c.
B ra c h y rh a p h is e p is c o p j
d.
P l a ty p o e c ilu s m a c u la tu s
6.
( F ig s . 5* 34*
( F ig s . 11,
55* 7 7 ).
28, 61, 8 3 ).
( F ig s . 14, 25, 6 4 , 86) .
( F ig s . 15, 24, 6 5 * 8 7 ).
A seco n d group in c lu d e s sev en s p e c ie s i n w hich th e b e h a v io r o f
t h e heterochrom osom es was a g a in t r u e t o ty p e .
The heterochrom osom es i n
t h e s e s p e c ie s w ere l i k e th o s e o f P seudoxlphophorus and Lim ia n i g r o f a s c i a t a
i n t h a t th e y d id n o t p o s s e s s m edian c o n s t r i c t i o n s .
However, s iz e d i f f e r ­
e n ce s betw een members o f a g iv e n p a i r co u ld n o t be e s ta b li s h e d o p t i c a l l y
a s t h e y c o u ld f o r L im ia and P seu d o x lp h o p h o ru s.
C.
a.
Lim ia v i t t a t a
( F ig s . 6 , 33* 56 ,
7 8 ).
b.
M o ll i e n i s i a sphenops
c.
M o ll i e n i s i a p e te n e n s is
( F ig s . 13, 26, 63 * 85) .
d.
G la r id ic h th y s f a l c a t u s
( F ig s . 8 , 31* 58, 8 0 ).
e.
Gambusia a f f i n i s h o lb r o o k ii
f.
Gambusia panuco panuco
( F ig s . 12, 27* 62, 84) .
g.
M ic r o p o e c ilia b r a n n e r i
( F ig s . 10, 29, 60, 8 2 ).
( F ig s . 7* 32, 57* 79).
( F ig s . 9* 30* 59* 8 1 ).
S t a t i s t i c a l A n a ly s is
G raphs o f t h e M easurem ents
A ll o f t h e c u rv e s o b ta in e d w ere a sy m m e tric a l o r p o s i t i v e l y skewed,
a skewed c u rv e b e in g one i n w hich th e mode and mean do not c o in c id e .
may be due i n p a r t t o t h e s m a ll s iz e o f each sam ple.
T h is
However, a c c o rd in g t o
Sim pson and Hoe (1939* p . 145)* m o d e ra te ly rig h t-s k e w e d d i s t r i b u t i o n s a r e
I common i n Z oology, w h ich means t h a t , i f i t h i n any g iv e n p o p u la tio n , la r g e
; v a r i a n t s a r e more common th a n s m a ll.
I
i
1.
G raphs from s p e c ie s i n w hich a d if f e r e n c e i n chromosome s iz e was
j
|
c y t o l o g i c a l l y o b s e rv a b le .
j
a*
P seu d o x ip h o p h o ru s b im a c u la tu s .
Upon t h e b a s is o f o p t i c a l
! e v id e n c e , i t may be rem em bered, i t was co ncluded t h a t th e h e t ero chromosomes
j
j
]
o f P seu d o x lp h o p h o ru s a r e n o t a l i k e , y e t Graph 1 shows a monomodal d i s t r i b u t i o n , p ro b a b ly p o s i t i v e l y skewed, a lth o u g h t h e in d e x f o r skew ness was
j
| not c a lc u la te d .
I n s p i t e o f t h e p re s e n c e o f one mode o n ly , th e skew ness
j
! and t h e e x tre m e ly t a l l n arrow c h a r a c te r o f t h e cu rv e p o in t t o t h e con­
c lu s i o n t h a t t h e cu rv e may be b im o d al, w ith t h e modes o f th e two c la s s e s
o f m easurem ents so c lo s e t h a t g ra p h in g o f th e d i s t r i b u t i o n o b sc u re s t h e b i —
ji
m o d a lity .
S in c e c y t o l o g i c a l e x am in atio n o f t h e germ c e l l s showed t h e h e-
j terochrom osom .es t o be o f d i f f e r e n t s i z e s , t h e d i s t r i b u t i o n o f t h e m easure­
1
m ents may be b im o d a l.
S t a t i s t i c a l a n a ly s is o f t h e d a ta may e s t a b l i s h t h e
b im o d a lity o f t h e d i s t r i b u t i o n and hence e n a b le one t o conclude t h a t
h e t erochrom osom es a r e o f d i f f e r e n t
b.
L e b is te s r e t i c u l a t u s .
th e
s iz e s .
Both sam ples o f 100 m easurem ents show
a d i s t i n c t bim o d al d i s t r i b u t i o n c o n s id e ra b ly skewed (G raph 2 , 3, 4 ) .
Cy­
t o l o g i c a l l y t h e heterochrom osom es o f t h i s s p e c ie s showed th e most marked
d iffe re n c e in s iz e .
P resum ably I n
s e p a r a te d t o g iv e Su g ra p h w hich i s
t h e s e cu rv es t h e modes a re w e ll enough
d i s t i n c t l y bim odal, and t h e r e f o r e
upon
in s p e c ti o n o f t h e cu rv e one may t e n t a t i v e l y conclude t h a t th e c y to lo g ic a l
o b s e r v a tio n has b een s u b s t a n t i a t e d and th e h et ero chromosomes a r e u n lik e i n
s iz e .
c.
I n s p e c t i o n o f t h e cu rv e o f Lim ia n i g r o f a s c i a t a shows i t t o
j b e b im o d al and p ro b a b ly l e s s skewed th a n t h e c u rv e s o f t h e p re c e d in g
j
j s p e c ie s (G raph 5)* The b im o d a lity , how ever, i s n o t a s d i s t i n c t as i n th e
j c a se o f L e b is t e s . T h is c o n c lu s io n i s i n l i n e w ith t h e c y to lo g ic a l e v i /
| d e n c e , w hich s u g g e s te d t h a t t h e s i z e d if f e r e n c e betw een th e h etero ch ro m o j somes o f Lim ia was n o t a s g r e a t a s t h a t found i n L e b is te s ,
|
2.
G raphs from s p e c ie s i n w hich c y t o lo g ic a l e v id e n c e was in d e te r m in a n t.
!
a . Group I . Those g ra p h s w hich by in s p e c tio n ap p e a r t o be s im ila r
j
j t o t h e g rap h o f t h e m easurem ents o f P seud o x lp h o p h o ru s.
|
The d i s t r i b u t i o n o f t h e m easurem ents o f M o llie n is ia sphenops seems
! t o be s i m i l a r t o t h a t o f P seudoxlphophorus (G raphs 6 , 1 ) , i n t h a t t h e curve
i s t a l l and s h a r p ly p eak ed .
One d if f e r e n c e betw een th e graphs i s t h a t s in c e
i shew ness t o t h e r i g h t i s n o t as pronounced i n t h e g ra p h o f M o ll i e n is ia , th e
; t o t a l d i s t r i b u t i o n may be more sy m m etrical and hence more n e a r ly approxim ate
i a n o rm al d i s t r i b u t i o n .
The t a l l peaked c h a r a c te r o f th e curve s u g g e s ts a
b im o d al d i s t r i b u t i o n i n w hich t h e two modes a r e v e r y c lo s e t o g e t h e r .
Thus
i t a p p e a rs t h a t t h e r e may be a s l i g h t d if f e r e n c e i n s iz e betw een t h e h e te r o chromosomes.
However, s in c e t h e d i s t r i b u t i o n a p p e a rs t o be more sy m m e tric a l,
t h e r e i s a p o s s i b i l i t y t h a t t h e curve does r e p r e s e n t a monomodal d i s t r i ­
b u tio n and hence t h e chromosomes may be t h e same s i z e .
S t a t i s t i c a l a n a ly s is
o f t h e d a ta may show w hich o f t h e s e two c o n c lu s io n s i s t h e more l i k e l y .
I n t h e g ra p h o f Gambusia panuco panuco (G raph 7)* t h e d i s t r i b u t i o n
i s a g a in t a l l and p eak ed , w ith t h e e x c e p tio n t h a t t h e curve on e i t h e r s id e
o f t h e a p p a re n t mode s lo p e s more g r a d u a lly .
The t o t a l d i s t r i b u t i o n i s pro ­
b a b ly more skewed t o t h e r i g h t th a n t h a t o f M o llie n is ia sphenops (G raph 6)
b u t a p p e a rs l e s s skewed th a n t h a t o f P seudoxlphophorus (G raph 1 ) .
A gain,
a s i n M o ll i e n i s i a sp h e n o p s, t h e d i s t r i b u t i o n may be bim odal o r monomodal
! b u t one cannot- d e c id e from i n s p e c ti o n o f t h e cu rv e w hich o f th e s e two
j
a l t e r n a t i v e s i s t h e more l i k e l y .
I f upon t h e b a s is o f s t a t i s t i c a l a n a ly s is
! o f t h e d a t a , t h e d i s t r i b u t i o n may be co n clu d ed t o be b im o d al, t h e chances
j
' a r e t h a t t h e chromosomes a r e n o t t h e same s i z e .
|
On th e o th e r hand, i f th e
r e s u l t s o f s t a t i s t i c a l a n a l y s i s su g g e st t h a t t h e cu rv e i s monomodal, one
| may p o s s i b l y co n clu d e t h a t t h e chromosomes a r e e q u a l i n s i z e .
|
j
The cu rv e o f M ic r o p o e c ilia b r a n n e r i (G raph 8 ) , i s a ls o s im i l a r
i n shape t o t h a t o f P seu doxlphophorus (G raph l ) . However, t h e r e a r e n o t
i
)
| a s many v a r i a t e s i n t h e ap p ro x im ate m odal c l a s s and t h e d i s t r i b u t i o n may
| be l e s s skewed t o t h e r i g h t .
|
F o r t h e same r e a s o n s , g iv e n and d is c u s s e d i n
c o n n e c tio n w ith t h e g rap h s of M. sphenops and G. panuco panuco, d e f i n i t e
c o n c lu s io n i n r e g a rd t o s i z e r e l a t i o n s h i p s m ust be d e f e r r e d .
j
|
b.
Group I I . Those g rap h s w hich by in s p e c tio n a p p e a r t o be
j
i s i m i l a r t o t h e g ra p h s o f L e b is te s r e t i c u l a t u s and Lim ia n i g r o f a s c i a t a .
The c u rv e s o f X iphophorus h e l l e r i i (G raph 9)* &nd o f L im ia n ig r o ­
f a s c i a t a (G raph 5)* a r e s i m i l a r .
The two modes i n t h e curve o f X iphophorus
a r e n o t as p eaked a s th o s e o f L im ia and seem t o be s e p a ra te d by a more
pronounced s in u s .
From in s p e c tio n o f th e c u rv e , i t would seem t h a t i n
X iphophorus t h e h e t e ro chromosomes a r e u n lik e i n s i z e .
C y fco lo g ically , how­
e v e r , no d i f f e r e n c e i n s iz e was d i s c e r n i b l e .
I n t h e g rap h o f t h e m easurem ents o f Gambusia h o lb ro o k ii (G raph
1 0 ) , t h e r e a p p e a rs t o be b im o d a lity and p o s it i v e skew ness.
The b im o d a lity
i s s l i g h t enough t o w a rra n t t h e c o n c lu s io n t h a t i t may have r e s u l t e d from
u s in g to o s m a ll a sam p le.
I f t h i s i s th e c a s e , t h e d i s t r i b u t i o n i s u n i-
m odal and t h e h e t e ro chromosomes may be o f t h e same s i z e .
The curve o f Braehyrhaphis e p isc o p i (Graph 1 1 ), i s s im ila r t o
t h a t o b ta in e d i n t h e seco n d sam ple o f L e b is te s r e t ic n la .t u s (G raph 3 ) .
In
I L e b i s t e s , how ever, t h e two modes seem t o be more w id e ly s e p a ra te d and skew—
j n e s s t o t h e r i g h t seems t o be l e s s pronounced.
From in s p e c tio n o f t h e
| c u rv e , i t a p p e a rs t h a t t h e h e t e ro chromosomes a r e n o t o f t h e same s i z e ,
i
|
c . Group I I I . Those c u rv e s w hich by in s p e c tio n do not resem b le
j
[ th o s e o f P se u d o x lp h o p h o ru s, L e b is t e s , o r L im ia.
I
!
The c u rv e s o f P la ty p o e c ilu s m a c u la tu s , Lim ia v i t t a t a and o f Mol­
l i e n i s i a p e te n e n s is (G raphs 12, 13, 1 4 ), seem t o be l i k e one a n o th e r .
The
g ra p h o f M o ll i e n i s i a p ro b a b ly shows t h e g r e a t e s t amount o f skew ness, w h ile
t h e d i s t r i b u t i o n i n P la ty p o e c ilu s and L im ia may be more sy m m e tric a l.
The
cu rv e s o f P la ty p o e c ilu s and Lim ia a r e p eak ed , f a l l i n g away q u ite s h a r p ly
on e i t h e r s id e o f t h e m odal c l a s s .
I n M o lli e n is ia , th e s lo p e o f th e curve
on e i t h e r s id e o f t h i s c l a s s i s more g r a d u a l.
I t i s im p o s s ib le t o a s c e r ­
t a i n th r o u g h i n s p e c ti o n w h eth er o r n o t th e d i s t r i b u t i o n i s bim odal and
th u s w h e th e r o r n o t t h e heterochrom osom es a r e o f u n e q u a l s i z e .
T h ree a sy m m e tric a l cu rv es (G raphs 15, 16, 1 7 ), were o b ta in e d w hich
w ere n o t a s t a l l and s h a r p ly peaked a s t h e curve o f Pseudoxlphophorus (G raph
1 ) , b u t w ere a g a in d e c id e d ly skewed t o t h e r i g h t .
These g rap h s o f th e
m easurem ents from G la ry d ic h th y s f a l c a t u s , H e te ra n d ria form osa and Q uintana
a t r i z o n a may be b im odal b u t t h e i r b im o d a lity i s n o t a p p a re n t t o th e ey e.
S t a t i s t i c a l a n a l y s is may show w h eth er o r not t h e d i s t r i b u t i o n i s bim odal
and hence w h e th er o r n o t t h e h e t e ro chromosomes a r e d i f f e r e n t i n r e s p e c t t o
s iz e .
S t a t i s t i c a l A n a ly s is o f R a tio s betw een th e P a i r s o f Het erochromosomes
The d i f f e r e n c e betw een t h e mean o f th e r a t i o s betw een m easurem ents
f o r an y g iv e n s p e c ie s and t h e means o f th e r a t i o s f o r each o f th e n in e te e n
o th e r s p e c ie s was d e te rm in e d and t e s t e d f o r s i g n i f i c a n c e .
The mean r a t i o s
f o r e a c h s p e c ie s and t h e s ta n d a rd e r r o r s o f th e means o f t h e r a t i o s a r e
l i s t e d i n T a b le 3.
T hese f ig u r e s were u sed t o d e term in e th e s ta n d a rd e r r o r
o f t h e d i f f e r e n c e betw een any tw o means com pared.
Each s p e c ie s was numbered
and t h e r e s u l t s o f t h e t e s t s e n te r e d u n d er t h e a p p r o p r ia te number i n T a b le
4*
A ll t h e t e s t s w hich w ere 3*50 and o v e r were c o n s id e re d s i g n i f i c a n t and
s t a r r e d when e n te r e d i n t h e t a b l e .
The number o f s i g n i f i c a n t t e s t s p e r
s p e c ie s was c o u n te d and t h e d i s t r i b u t i o n o f s p e c ie s w ith r e s p e c t t o th e
number o f s i g n i f i c a n t t e s t s was d e te rm in e d and p l o t t e d i n Graph IBB,
The means o f X iphophorus h e l l e r i i (No. 3)> Gambusia panuco panuco
(No. 6 ) , M o ll i e n i s i a p e te n e n s is (No. 1 2 ), M ic r o p o e c ilia b r a n n e ri (No. 16)*
B ra e h y rh a p h is e p is c o p i (No. 2 0 ), and P la ty p o e c ilu s m ac u la tu s (No. 21) o n ly
d i f f e r e d s i g n i f i c a n t l y from th e means o f L e b is te s r e t i c u l a t u s (No. 14) and
G ir a rd in u s met a l i i cus (No. 17) (T ab le 4 ) .
The f ig u r e s i n T ab le 5 have been
ta k e n from T a b le 4 , and show t h a t t e s t s betw een t h e s e s i x s p e c ie s were not
s ig n ific a n t.
___ _______________________________________________________
TABLE 5
S p e c ie s
3
3
6 •
12
16
20
21
1.310, 0 .6 5 2
1 .4 7 0
0.935
0 .1 0 1
0.746
1.000
2 .5 5 0
1 .790
1 .410
0 .543
0 .3 2 1
1 .560
6
1 .3 1 0
---------
12
0 .6 5 2
3 .150
16
1 .4 7 0
0.746
1 .790
20
0.935
1 .0 0 0
1 .410
0 .3 2 1
21
0 .1 0 1
2 .550
0 .543
1 .5 6 0
3.150
1 .4 1 0
1.410
---------
Thus upon t h e b a s i s o f th e s e r e s u l t s , th e s e s i x s p e c ie s may be grouped t o ­
g e th e r (G raph 18B ).
S in c e t h e group as a whole i s s i g n i f i c a n t l y d i f f e r e n t
61
TABLE 3
S p e c ie s
Mean o f
R a tio s
S ta n d a rd e r r o r s
o f Means o f
R a tio s
P o e c i l i s t e s p l e u r o s p i l u s G uenther
1.085
0 .009
P seu d o x lp h o p h o ru s b im a c u la tu s H eckel
1 .0 2 8
0.006
X iphophorus h e l l e r i i H eckel
1*055
0 .0 0 7
P o e c i l i o p s i s in f a n s Hubbs
I .O 75
0 .0 0 8
P la ty p o e c ilu s v a r i a t u s Meek
1*075
0.0 1 2
Gambusia panuco panuco Hubbs
1.073-
0 .0 1 0
L im ia n i g r o f a s c i a t a Began
1.083
0 .009
L im ia v i t t a t a G uichenot
1 .0 6 7
0 .0 0 8
Q u in ta n a a t r i z o n a Hubbs
1.045
0 .0 0 5
M o l l i e n i s i a sphenops C u v ier and V ale n c ie n n e s
1 .0 4 2
0 .0 0 8
M o ll i e n i s i a p e te n e n s is Hubbs
1.049
0.006
G la r id ic h th y s f a l c a t u s Eigenmann
1.063
0.0 0 8
L e b is te s r e t i c u l a t u s
1.230
0.014
H e te r a n d ria form osa A g a ssiz
1.042
0.005
M ie r o p o e c ilia b r a n n e r i Eigenmann
1*073
0 .010
G ira rd in u s m e t a l i i c u s Poey
I .330
0.023
M o ll i e n i s i a l a t i p i n n a LeSueur
1.042
0.005
Gambusia a f f i n i s h o lb r o o k ii G ira rd
1 .0 6 4
0 .0 0 7
B ra c h y rh a p h is e p is c o p i S te in d a c h n e r
1 .068
0 .012
P la ty p o e c ilu s m a c u la tu s G uenther
1.0 5 4
0 .0 0 7
P e te r s
62
KEY t o TABLE 4
Numb'
Name o f S p ecies
1
P o e c i l i s t e s p le u r o s p ilu s G uenther
2
F seudoxiphophorus b im a c u la tu s H eckel
3
X iphophorus h e l l e r i i H eckel
4
P o e c ilio p s is in f a n s Hubbs
5
P la ty p o e c ilu s v a r i a t u s Meek
6
Gambusia panuco panuco Hubbs
8
Lim ia n i g r o f a s c i a t a Reg^n
9
Lim ia v i t t a t a G uichenot
10
Q uin tana a tr iz o n a Hubbs
11
M o llie n is ia sphenops C uvier and V a le n c ie n n e s
12
M o llie n is ia p e te n e n s is Hubbs
13
G la r id i c h t hys f a l c a t u s Eigenmann
14
L e b is te s r e t i c u l a t u s P e te r s
15
H e te ra n d ria form osa A gassiz
16
M ic ro p o e c ilia b r a n n e ri Eigenmann
17
G ira rd in u s met a l i i c u s Poey
18
M o llie n is ia l a t i p i n n a LeSueur
19
Gambusia a f f i n i s hoirbrook-i i G ira rd
20
B racb y rh ap h is e p is c o p j G beindachner
21
P la ty p o e c ilu s m acu la tu s G uenther
S ig n ific a n c e beti
S p e cies
Numbers
1
2
5 .28*
1
6
8
9
10
u
4
5
2 .6 3
0 .833
0.666
1 .0 4
0.157
1 .5 0
3 .8 t*
2.9 3
4.70*
3.50*
3 .2 1
5.09*
3 .9 0 *
2.1 8
1*40a
1 .8 8
1 .4 4
1 .3 1
2.4 5
1 .1 3
1.16
1. 23I
0.000
0.3-12
0.675
0 .7 0 8
3.18
2.92
0 .2 5 7
1.2 0
0 .6 2 5
2 .3 1
2. 2fi
0.895
0 .3 1 2
2.3 2
2.261
1 .3 3
3.69*
3 . 4#
3
2
5.28*
3
2 .6 3
2 .9 3
4
0.833
4.70*
1 .8 8
5
0.666
3.50*
1 .4 4
0.000
6
1 .0 4
3 .2 1
1 .3 1
0.312
0 .2 5 7
S
0 .1 5 7
5.09*
2.4 5
0 .675
1 .2 0
0.895
9
1 .5 0
3.90*
1 .1 3
0.708
0.625
0.312
1 .3 3
2 .3 4
2.2J
....
0. 31^
10
3 . 88*
2 .1 8
1.16
3 .1 8
2 .3 1
2 .3 2
3.69*
2 .3 4
11
3-58*
1 .4 0
1.2 3
2 .9 2
2.29
2.2 6
3.4 2
2 .2 1
0.319
12
3.3 3
2 .4 7
0.652
2 .6 0
1 .9 4
1 .6 4
3.15
1 .8 0
0.513
0.700
13
1 .8 3
3.50*
0.755
1.0 6
0.833
0.625
1.7 5
0 .3 5 4
1 .9 1
1.36 i
14
8 .73* 13.29* 1 1 . 22*
9.63*
8.97*
9.24*
8 . 86* 1 0 . 12* 1 5 . 20* liiM *
15
4.17*
1 .5 1
3 .51*
2 .5 4
2 .5 8
3.98*
2 .6 5
0.423
1 .4 7
0.156
0 .1 2 8
0.142
0.746
O.468
2.3 3 ' ^ 2 . 42^
1.7 9
f
16
0.895
17
9.92* 12.74* 11.46* 1 0 . 90* 10 . 23* 10.34* 10 . 00* 10.82* 12.13* 11.8^
18
3 .3 1
1 .7 9
1 .5 1
3.51*
2 .5 4
2 .5 8
3 .9 8 *
2 .6 5
0.423
O.M
19
1 *84
3 • 91*
0 .999
1 .0 4
0 .7 9 1
0 .5 7 4
1.6 6
0 .2 8 3
2 .2 1
2.0M
20
1 .1 3
2 .9 8
0.935
o . 486
.0414 0 .1 2 8
1 .0 0
.069
1.72
l,8 1 j
21
2 .7 2
2 .8 3
0 .1 0 1
1 .9 8
1 .0 5
1. 1M
S = 3*5 and o v e r
* = S ig n ific a n t
3.3 5
1 .5 1
1 .3 9
2 .5 5
1 .2 2
ins from 20 s p e c ie s
.2
13
13
1 .8 3
•7
14
. 1 -18 .7 3 *
15
16
17
18
19
20
21
4 .1 7 *
1 .8 4
1 .1 3
2 .7 2
4 .1 7 *
0 .895
9 .9 2 *
3.50* 1 3 .29*
1 .7 9
3 .3 5
1 2 . 74*
1 .7 9
3 .9 1 *
2 .9 8
2 .8 3
'52
0.755 1 1 . 22*
1 .5 1
1 .4 7
1 1 . 46*
1 .5 1
0.999
0.935
0 .101
0
1.06
9 .6 3 *
3 .5 1 *
0.156 10. 90*
3.51*
1 .0 4
0.486
1 .9 8
4
0 .8 3 3
8 .9 7 *
2 .5 4
0 .1 2 8 1 0 . 23*
2 .5 4
0 .7 9 1
4
0.625
9 .2 4 *
2 .5 8
*0142 10.34*
2 .5 8
0 .5 7 4
0.1 2 8
1 .3 9
5
1 .7 5
8 . 86*
3 .9 8 *
0.746 1 0 . 00*
3-98*
1.6 6
1 .0 0
2.55
0
0 .3 5 4 1 0 . 12*
2 .6 5
O.468 10.82*
2 .6 5
0.-283
0.0 6 9
1 .2 2
13
1 .9 1
1 5 . 20*
0 .4 2 3
2 .3 3
12.13*
0 .4 2 3
2 .2 1
1 .7 2
1.0 5
00
1.8 6
11 . 6 7 *
0 .0 0 0
2 .4 2
11.85*
0 .0 0 0
2 .0 8
1 .8 1
1.1 3
1 .4 0
1 1 .91*
0 .8 9 7
1 .7 9
1 1 . 88*
0 .8 9 7
1.6 3
1 .4 1
0.543
1 0 .3 7 *
2 .2 3
0 .7 8 1 10.99*
2 .2 3
0 .9 4 3
0 .3 4 7
0.849
0
il* 10. 3 ?*
97 2 .2 3
:9
0 .7 8 1
la* 10.99*
97 2 .2 3
1 2 . 70*
1 2 . 70*
9 .1 3 *
9 .1 3 *
2 .5 8
2 .5 8
3.72* 1 2 . 70* 10.64*
0 .0 0 0
2 .5 8
8.80* 11.28*
12.2 6 *
0 .0 0 0
2.56
2 .6 0
1 .4 0
10.28*
2 .5 8
0 .7 3 8
0 .3 2 1
1.5 6
12.2 6 * 11.08* 10.12* 11.50*
3 .7 2 * 12 .2 6 * 1 0 .28*
1 2 .70*
.0 4 1 / 1 .5 1
2.56
12.26*
3
0.943 10 .6 4 *
2 .5 6
0 .7 3 8 11.08-*
2.5 6
1
0 .3 4 7
8 .8 0 *
2 .0 0
0 .3 2 1 10.12*
2 .0 0
0 .2 3 7
43 0.849 1 1 .2 8 *
1 .4 0
1.5 6
11.50*
1 .4 0
0 .7 2 0
2 .0 0
1 .4 0
0 .2 3 7
0.720
1 .4 1
1 .4 1
from fe w e r s p e c ie s th a n any o f t h e o th e r f o u r te e n s p e c ie s , one may t e n t a ­
t i v e l y co n clu d e t h a t t h e heterochrom osom es w ith in each s p e c ie s a r e a lik e .The d i f f e r e n c e betw een t h e mean r a t i o s i n Lim ia v i t a t t a (No. 9)>
M o ll i e n i s i a sphenops (No. 1 1 ), G la rv d ic h th y s f a l c a t u s (No. 13) > and Gam­
b u s ia a f f i n i s h o lb r o o k ii (No. 1 9 ), were n o t s i g n i f i c a n t .
The r e s u l t s o f
t h e t e s t s shown i n T a b le 6 w ere o b ta in e d from T a b le 4*
TABLE 6
S p e c ie s
5*
11
9
19
13
5
------------------------
0.625
2 .2 9 0
0 .833
0 .7 9 1
9
0 .6 2 5
------------------------
2 .2 1 0
0 .3 5 4
0 .2 8 3
11
2 .2 9 0
2 .2 1 0
------------------------
1 .8 6 0
2 .080
13
0 .8 3 3
0 .3 5 4
1.8 6 0
------------------------
0 .9 4 3
19
0 .7 9 1
0 .283
2 .080
0 .943
X
S p e c ie s w ith compound h et ero chromosomes
From t h e d a t a , t h e r e f o r e , th e s e fo u r s p e c ie s form a group i n w hich t h e
h e t e ro chromosomes o f eac h s p e c ie s may n o t be q u it e th e same s i z e .
However,
G raph 18B shows t h a t th e s p e c ie ^ i n group 1 and th o s e i n group 2 d i f f e r
o n ly i n r e s p e c t t o a s i n g l e a d d i t i o n a l s i g n i f i c a n t t e s t .
Hence i t i s
p o s s i b l e t h a t i f t h e s i z e o f th e sam ples from t h e s e t e n s p e c ie s were i n ­
c r e a s e d , s t a t i s t i c a l a n a l y s is m ight show t h a t th e y a r e a l l i n th e same
g ro u p , o r m ight show t h a t t h e d if f e r e n c e s betw een t h e groups i s g r e a t e r
th a n i t a p p e a rs t o be i n t h i s in s t a n c e .
Q u in ta n a a t r i z o n a (No. 10) i s s i g n i f i c a n t l y d i f f e r e n t from f o u r
o f t h e n in e te e n o th e r s p e c ie s (T ab le 4.).
s p e c ie s may be s l i g h t l y d i f f e r e n t i n s i z e .
Thus th e h e t e ro chromosomes i n t h i s
P resum ably, w h ile th e d i f f e r e n c e
b etw een t h e chromosomes o f a p a i r i s n o t l a r g e , th e d if f e r e n c e betw een them
i s g r e a t e r th a n t h a t betw een th e chromosomes i n th e p re c e d in g two g ro u p s.
H e te r a n d ria form osa (No. 15) i s s i g n i f i c a n t l y d i f f e r e n t from f i v e
o f t h e n in e te e n s p e c ie s (T ab le 4 ) .
A gain th e d if f e r e n c e s betw een th e mem­
b e r s o f t h e p a i r o f h e t e ro chromosomes a r e p ro b a b ly g r e a t e r th a n th e d i f ­
f e r e n c e s betw een t h e chromosomes i n t h e p re c e d in g groups (G raph 18B ).
The n e x t t h r e e s p e c ie s shown on g ra p h 18B p o s s e s s chromosomes
w hich d i f f e r enough from one a n o th e r f o r t h e d i f f e r e n c e s t o be d i s t i n ­
g u is h a b le c y t o l o g i c a l l y .
The mean r a t i o o f L e b is te s r e t i c u l a t u s (No. 14)
d i f f e r e d s i g n i f i c a n t l y from t h e mean r a t i o s o f a l l o f t h e o th e r s p e c ie s ,
t h a t o f P seu d o x ip h o p h o ru s (No. 2) d i f f e r e d from n in e o th e r s p e c ie s , w h ile
t h a t o f Lim ia n i g r o f a s c i a t a (No. 8) d i f f e r e d from s i x .
S p e c ie s w ith Compound Heterochromosom es
A.
I n tr o d u c ti o n
As was done i n t h e c a se o f s p e c ie s e x h ib i tin g two heterochrom o­
som es, i t m ight be w e ll t o p re c e d e t h e d e s c r ip t io n o f t h e b e h a v io r o f com­
pound h e t e ro chromosomes i n P o e c i liid a e w ith a g e n e r a l d is c u s s io n o f t h e be­
h a v io r o f compound s e x -d e te rm in in g chromosomes.
F or th e p u rp o se s o f f u r ­
t h e r s tu d y c r i t e r i a may be e s ta b lis h e d w hich w i l l prove u s e f u l i n d e c id in g
w h eth er o r n o t t h e compound h e t ero chromosomes t o be d e s c rib e d a r e s e x - d e t e r ­
m in in g com plexes.
1.
The h i s t o r y o f t h e compound form s d u rin g th e grow th p e r io d i s not
e n tire ly c le a r.
From t h e e v id en c e on hand, th e y seem t o undergo a p ro c e s s
o f h e te ro p y c n o s is s i m i l a r t o t h a t seen i n t h e sim p le ty p e s .
I n some i n ­
s ta n c e s t h e X com ponents seem t o form a s in g le la r g e n u c le o lu s a s s o c ia te d
w ith a plasm osom e.
I n o th e r in s ta n c e s t h e components o f t h e XT com plex
rem ain d i s t i n c t b u t become imbedded i n a la r g e plasmosome.
2*
I n t h e s y n a p s is o f t h e m ale, X com ponents come t o g e t h e r i n a g ro u p .
At t h e tim e o f t h e e q u a tio n a l d i v i s i o n ea c h X component s p l i t s le n g th w is e ,
w h ile i n t h e h e t e r o k i n e t i c d i v i s i o n t h e e n t i r e group p a s s e s u n d iv id e d t o
one pole..
3-
D u rin g h e t e r o k i n e s i s t h e X complex may show p r e c e s s io n o r su c c e s­
s io n , t h e w hole com plex b e h a v in g a s a s in g l e u n i t .
U*
As I n t h e sim p le ty p e t h e p o s it i o n o f t h e X complex i n r e s p e c t t o
t h e e q u a t o r i a l p l a t e i s c o n s ta n t.
5.
F o r any one s p e c i e s , elem en ts fo rm in g t h e X complex a r e c o n s ta n t
i n s iz e and sh a p e .
However, betw een s p e c ie s t h e r e i s c o n s id e ra b le v a r i a ­
b i l i t y , f o r t h e com ponents o f t h e X group may be o f e q u a l o r u n e q u a l s i z e .
As a r u l e , i n la r g e X com plexes one chromosome i s commonly la r g e and t h e
rem ain d er s m a ll.
6.
Compound ele m e n ts fo rm in g th e X com plex have been found t o v a r y
from 2 t o 8 o r more i n number b u t f o r a g iv e n s p e c ie s a r e alw ays c o n s ta n t
i n num ber.
7.
W hatever be t h e i r num bers, th e X group may be d ouble i n t h e fem ale
an d s in g l e i n t h e m a le, t h u s c o rre s p o n d in g t o t h e P r o te n o r ty p e (XX - XO),
o r be opposed by a s i n g l e Y chromosome i n t h e m ale and th u s o f t h e Droso­
p h i l a ty p e (XX - XY).
8.
I n d is c u s s in g s p e c ie s showing t h e D ro so p h ila ty p e , W ilson (1928,
p . 767 ) } s t a t e s :
j1I n a l l c e r t a i n l y known c a s e s t h e Y elem ent i s a s in g le
chromosome w hich shows no te n d e n c y t o b re a k up i n t o s e p a r a te components
such' a s o f te n a p p e a rs i n t h e c a s e o f t h e X e l e m e n t A m o n g p l a n t s a few
c a s e s o f compound Y have been r e p o r te d .
Among a n im a ls , how ever, a com­
pound Y elem en t has o n ly been d e s c r ib e d f o r t h e hom opteran Pseudococcus
66
(W ilso n , 192S, p . 767)*
b o th s e x e s .
I n P seudococcus t h e d ip l o i d number i s t e n f o r
I n t h e fe m a le , d u rin g m a tu r a tio n , f i v e norm al t e t r a d s a r e
form ed and t h e m a tu r a tio n d i v i s i o n s a r e n o rm a l.
I n t h e m ale, f i v e o f t h e
chromosomes rem ain i n a compact group d u r in g t h e grow th p e r io d , d iv id in g
e q u a tio n a lly in th e f i r s t d iv is io n .
I n t h e se co n d ary sp e rm ato cy te d i v i -
- s io n , t h e f i v e h e te r o ty p ic chromosomes p a s s t o one p o le and t h e f i v e a u to ­
somes t o t h e o t h e r .
The c o n c lu s io n i s t h a t a l l t e n chromosomes i n th e
fem ale r e p r e s e n t X com ponents and th e f i v e o f th e m ale a r e c o n fin e d to
1 t h a t s e x a lo n e , so t h a t t h e y a r e an alo g o u s t o a compound Y ele m e n t.
9*
The s in g l e Y chromosome may be l a r g e r th a n any i n d iv id u a l X com­
pon en t a s i n t h e h e m ip te ra n s P s e llio d e s s p .,- P rio n id u s s p . . and Ac h o lla
m u ltis p in o s a .
I n some c a s e s Y may be e q u a l i n s i z e t o one o r more o f th e
X com ponents a s i n t h e h e m ip te ra n Thy a n t a c a l c e a t a , i n t h e nem atode A s c a ris
in c u r v a and i n t h e c o le o p te r a n B laps l u s i t a n i c a (W ilson, 1928, p . 776).
T h u s, w h ile t h e X elem ent may be compound, i t i s d e f i n i t e l y o r ­
g a n iz e d Y jith r e s p e c t t o s i z e and number and b e h a v io r.
The b e h a v io r o f th e
whole group i s s i m i l a r t o t h a t o f a s in g l e X chromosome o p e r a tin g i n an
XX - XO, XX - XY ty p e o f s e x m echanism.
S p e c ie s w ith t h r e e heterochrom osom es
1.
C y to lo g ic a l O b s e rv a tio n s .
F o u r o f t h e tw e n ty s p e c ie s o f P o e c il iid a e o b serv ed p o s se s se d
t h r e e heterochrom osom es.
S in c e t h e b e h a v io r o f th e s e chromosomes was
s i m i l a r i n a l l f o u r , G ira rd in u s met a l i i cus has been s e le c t e d f o r th e ty p e
form upon w hich th e g e n e r a l d e s c r i p t i o n w i l l be b a se d .
The rem ain in g t h r e e
s p e c ie s w i l l be d is c u s s e d b r i e f l y , p a r t i c u l a r l y em p h asizin g any d e v ia tio n
from t y p e .
a.
G ir a rd in u s m e t a l i i c u s Poey.
T h e re i s a s tr o n g p o s s i b i l i t y t h a t th e heterochrom osom es undergo
a p r o c e s s o f h e te ro p y c n o s is d u r in g t h e grow th p e r io d .
Near t h e n u c le a r
w a ll o f t h e l e p t o t e n e and sy n a p te n e n u c le i a r e t h r e e d a rk ly s t a i n i n g com­
p a c t b o d ie s .
o b s e rv e d .
B e g in n in g w ith t h e p a c h y te n e s ta g e two such b o d ie s may be
The l a r g e r o f t h e two b o d ie s a p p e a rs d u m b -b ell shaped and d o u b le .
Some o f t h e n u c le i i n t h e d i f f u s e s ta g e f o llo w in g t h e p o s t- s y n a p tic spirem e
c o n ta in one e x tre m e ly l a r g e n u c le o lu s w hich may r e s u l t from a c lo s e a s s o ­
c i a t i o n o f two X com ponents w ith a s in g l e Y.
F u r th e r s tu d y i s n e c e s s a r y
b e f o re one can c o n clu d e w ith any d e g re e o f r e a s o n a b le c e r t a i n t y t h a t th e s e
d a r k ly s t a i n i n g b o d ie s r e p r e s e n t h e te r o p y c n o tic se x chromosomes.
F o llo w in g t h e grow th p e r io d , t h e chromosomes o f t h e p rim a ry s p e r ­
m a to cy te d i v i s i o n a p p e a r a s a r e s u l t o f c o n d e n s a tio n o f th e spirem e i n
t h e d i f f u s e s ta g e .
The autosom es become m assed i n t h e c e n te r o f t h e s p in d le
w h ile t h e heterochrom osom es l a g b e h in d them .
They may be d is tin g u is h e d as
a la r g e t r i p a r t i t e body s i t u a t e d a t t h e edge o f th e e q u a t o r i a l p l a t e , b u t
c o n n e c te d t o t h e group o f autosom es by a s p in d le f i b e r ( F ig . 1 7 )-
A la te r
s ta g e shows t h e t r i p a r t i t e body t o have s e p a r a te d i n t o two u n eq u a l p a r t s .
The l a r g e r o f t h e t w o ,p a r t s i s d i s t i n c t l y double ( F ig . 2 2 ), b u t soon d i ­
v id e s i n t o tw“o , so t h a t one o b se rv e s t h r e e heterochrom osom es a t t h e p e r i ­
p h e ry o f t h e s p in d le ( F ig . 2 1 ) .
At t h i s tim e t h e p o s it i o n o f th e t h r e e
a s s o c i a t e d heterochrom osom es w ith r e s p e c t t o th e autosom es and s p in d le i s
q u i t e c o n s ta n t.
compact r o d s .
The h e t e ro chromosomes th e m se lv e s a r e i n th e form o f sm a ll
As w e ll a s co u ld be d e te rm in e d , m edian c o n s t r i c t i o n s sug­
g e s ti v e o f t h e p la n e o f c le a v a g e i n th e second sp erm ato cy te d i v is io n were
not p re s e n t.
U n d o u b ted ly t h e t r i p a r t i t i o n o f th e " s in g le " chromosome r e p r e ­
s e n ts t h e h e t e r o k i n e t i c d i v i s i o n .
The d i v is io n i s n o t s im u lta n e o u s , how­
e v e r , s in c e one o f t h e chromosomes, p ro b a b ly th e one w hich p a s s e s t o t h e
p o le a lo n e , s e p a r a t e s from t h e group s l i g h t l y i n advance o f th e o th e r s .
Two o f t h e t r i a d p a s s t o one p o le o f t h e s p in d le and t h e rem ain in g one i n
t h e o p p o s ite d i r e c t i o n .
As a r u l e th e y re a c h t h e p o le s b e fo re t h e a u to ­
somes d iv id e ( F ig . 67) •
Thus t h e b e h a v io r o f t h e compound h et e ro chromosomes p a r a l l e l s
t h a t o f t h e s i n g l e p a i r , f o r t h e r e i s a d e la y i n a p p ro a c h in g t h e m etaphase
p l a t e , a p re c o c io u s d i v i s i o n and a p re c o c io u s an ap h a se .
S im ila r ly t h e r e
i s a te m p o ra ry s e p a r a t i o n o f t h e autosom es j u s t , b e f o r e d iv is io n so t h a t
p o l a r v iew s show ing t h e i n d i v i d u a l chromosomes may be o b se rv e d .
I n th o s e
p o l a r v ie w s, s e c tio n e d p a r a l l e l t o t h e l o n g i t u d i n a l a x is o f th e s p in d le ,
t h e h e t ero chromosomes co u ld be se e n a t t h e p e r ip h e ry o f t h e group o f a u to ­
som es.
I n some o f t h e f i g u r e s two o f them were a p p a re n t and i n o th e r s o n ly
one ( F ig s . 89, 9 0 ) .
S in c e t h e o n ly case o f a compound Y chromosome among a n im a ls has
b een d e s c rib e d f o r P seu d o co ccu s, a form i n w hich th e whole c y t o lo g ic a l p i c ­
t u r e i s so a t y p i c a l t h a t o th e r i n t e r p r e t a t i o n s cannot be ex clu d ed , one may
co n clu d e w ith a f a i r m arg in o f s a f e t y t h a t i n G ira rd in u s t h e two h e te r o chromosomes p a s s in g t o one p o le may be c o n s id e re d a s an X complex made up
o f tw o component p a r t s .
I t th e n fo llo w s t h a t th e s in g le chromosome p a s ­
s in g t o t h e o p p o s ite p o le i s a Y chromosome.
O b se rv a tio n s o f c e l l s from
s e v e r a l specim ens o f G ira rd in u s show th e number o f components i n t h e X com­
p le x t o be c o n s ta n t i n number and s i z e .
The Y component i s much l a r g e r
th a n one o f t h e X com ponents and may be l a r g e r th a n t h e second ( F ig . 6 7 ) .
b.
P o e c i l i o p s i s in f a n s and M o lli e n is i a l a t i p i n n a
As f a r a s one can d e te rm in e th ro u g h o b s e r v a tio n , t h e b e h a v io r and
m orphology o f t h e heterochrom osom es i n th e s e two s p e c ie s a r e v e r y s im i la r
t o th o s e i n G ir a r d in u s .
o f t h e X com ponents.
The s i n g l e Y chromosome seems l a r g e r th a n e i t h e r
I f t h e r e a r e d if f e r e n c e s i n s iz e betw een th e X com­
p o n e n ts i n e i t h e r s p e c ie s th e y cannot be d e te rm in e d by o b s e rv a tio n ( F ig s .
1 9 , 2 0 , 4 3 , 4 4 , 4 5 , 4 6 , 6 9 , 70, 9 3 , 9 4 , 9 5 , 9 6 ) .
c.
P l a ty p o e c ilu s v a r i a t u s Meek
W hile i n P la ty p o e c ilu s v a r i a t u s t h e h e t e ro chromosomes a r e l i k e
th o s e o f t h e ty p e form i n r e s p e c t t o b e h a v io r and g e n e ra l s t r u c t u r e , t h e
chromosomes th e m s e lv e s may a l l be o f one s i z e .
At l e a s t , any d if f e r e n c e s
betw een them a r e p ro b a b ly to o s l i g h t t o d e t e c t , e s p e c i a l l y when t h e elem ent
o f s e c t io n i n g h as t o be ta k e n i n t o acco u n t ( F ig s . 40, 47^ 4^
2.
71^ 97^ 98) .
S t a t i s t i c a l A n a ly s is
a.
Graphs o f t h e m easurem ents.
The m easurem ents o f G ira rd in u s met a l i i cus show a d e f i n i t e l y t r i m odal d i s t r i b u t i o n , w ith q u i t e deep s in u s e s betw een t h e modes (G raph 19)*
From i n s p e c ti o n i t would seem t h a t each heterochrom osom e i s a d i f f e r e n t
s iz e .
The c u rv e s o f P o e c i l i o p s i s in f a n s and M o lli e n is ia l a t i p i n n a a r e
b o th b im odal and seem t o be o f t h e same g e n e r a l ty p e (G raphs 20, 2 1 ).
In
t h e cu rv e f o r e a c h o f t h e s e s p e c ie s one o f th e modes com prises about tw o t h i r d s o f t h e a r e a o f t h e c u rv e .
I n s p e c tio n a l a n a ly s is o f th e cu rv es le a d s
one t o t h e c o n c lu s io n t h a t one o f th e chromosomes i n each s p e c ie s a p p e a rs
t o d i f f e r from t h e o t h e r s .
The m easurem ents from P la ty p o e c ilu s v a r i a t u s a r e r a t h e r sym m etri­
c a l l y d i s t r i b u t e d and th e cu rv e has o n ly one mode (G raph 2 2 ) .
From t h i s
cu rv e one m ig h t e x p ec t th a t, a l l t h r e e o f t h e heterochrom osom es a r e o f th e
same s i z e .
b.
S t a t i s t i c a l A n a ly s is o f th e D if fe r e n c e s betw een th e S in g le
Y chromosome and t h e Mean o f t h e Two X Components.
When t h e m easurem ents o f th e s in g l e Y chromosome i n G ira rd in u s
met a l i i cus w ere com pared t o t h e mean o f th e m easurem ents o f th e two X com­
p o n e n ts , a v a lu e f o r t o f 2 .8 0 1 3 was o b ta in e d .
The v a lu e f o r t c o r r e s ­
p o n d in g t o a p r o b a b i l i t y o f 1 p e r c e n t i s 2 .6 8 0 , a lo w er v a lu e th a n t h a t
o b ta in e d from t h e d a t a .
T h e re f o re , th e d if f e r e n c e betw een th e m easurem ents
o f t h e Y chromosome and t h e means o f t h e m easurem ents o f th e X chromosomes
d i f f e r more th a n w ould be e x p e c te d i n a random sam p lin g from a homogeneous
p o p u la tio n .
However, s in c e t h e m easurem ent o f Y was compared t o a mean and
n o t t o a n o th e r s i n g l e m easurem ent one cannot conclude on t h e b a s is o f t h i s
t e s t a lo n e t h a t t h e Y i s l a r g e r th a n e i t h e r one o f th e two X chromosomes.
T h e o r e t i c a l l y t h e Y may b e t h e same s iz e a s one o f th e two X com ponents.
F or exam ple, suppose t h e chromosomes i n th e X complex m easure 3 m ic ra and
5 m ic ra w ith a mean o f 1 m ic ra and t h e Y chromosome a ls o m easures 5 m ic ra .
I n t h i s h y p o t h e t i c a l c a s e , t h e n , th e m easurem ent o f th e s in g le Y d i f f e r s
from t h e mean o f t h e two m easurem ents b u t t h e Y i s a c t u a l l y t h e same s iz e
a s one o f t h e X chromosomes.
T h us, on th e b a s is o f t h i s t e s t a lo n e , one
can co n clu d e m e re ly t h a t th e Y chromosome may be l a r g e r th a n b o th o f t h e
X chromosomes o r t h a t i t may be s im il a r i n s iz e t o one o f them and l a r g e r
th a n t h e o t h e r .
I n o r d e r t o d e c id e w hich o f th e s e a l t e r n a t i v e s i s most
p ro b a b le so m eth in g must be known about th e s iz e r e l a t i o n s h i p betw een th e
two X chromosomes.
Com parison betw een t h e m easurem ents o f th e Y chromosome w ith t h e
means o f t h e m easurem ents o f t h e two X components gave th e same r e s u l t s
f o r t h e s p e c ie s P o e c i l i o p s i s i n f a n s and M o llie n is ia l a t i p i n n a .
f o r P o e c i l i o p s i s i s 3 .5 5 w h ile t h a t f o r M o llie n is ia i s 4 . 6 1 .
The t v a lu e
Both o f t h e s e
v a lu e s a r e c o n s id e r a b ly h ig h e r th a n t h e v a lu e 2 .6 8 0 , w hich i s th e v a lu e o f
t c o rre s p o n d in g t o a p r o b a b i l i t y o f 1 p e r c e n t.
The same l i n e o f re a s o n in g
d is c u s s e d i n c o n n e c tio n w ith th e r e s u l t s o b ta in e d f o r G ira rd in u s a p p lie s
a g a in i n t h i s i n s t a n c e .
T h e re f o re , one cannot conclude t h a t Y i s d e f i n i t e l y
l a r g e r th a n b o th o f t h e X chromosomes u n le s s one knows more about th e s iz e
r e l a t i o n s h i p b etw een t h e s e two chromosomes.
F o r P la ty p o e c ilu s v a r i a t u s t h e v a lu e o f t i s 0 .7 3 0 , a f ig u r e much
lo w er th a n 2 .6 8 0 , t h e t v a lu e a t th e 1 p e r ce n t p o i n t .
Thus, th e Y chromo­
some i n t h i s s p e c ie s does n o t d i f f e r s i g n i f i c a n t l y from t h e mean o f th e
two X com ponents.
I t I s p o s s i b l e , how ever, f o r two d i f f e r e n t s iz e s o f X
chromosomes t o have a mean w hich would n o t be v e ry d i f f e r e n t from t h e mea­
surem ent o f t h e Y chromosome.
T hus, i n t h i s case as i n t h e p re c e d in g o n e s,
d e f i n i t e c o n c lu s io n s a r e n o t i n o rd e r u n t i l th e s iz e r e l a t i o n s h i p betw een
t h e X chromosomes has b een a s c e r t a in e d .
c.
S t a t i s t i c a l a n a ly s is o f t h e r a t i o s betw een th e two X com ponents.
The mean o f t h e r a t i o s betw een th e m easurem ents o f th e two X com­
p o n e n ts i n G ira rd in u s m e t a l l i c u s was s i g n i f i c a n t l y d i f f e r e n t from t h e mean
r a t i o s o f a l l o th e r s p e c ie s (T ab le 4 ) .
Graph 18A shows t h a t i n G ira rd in u s
(No. 17) and L e b is te s (No. 14) t h e r e s u l t s were s i g n i f i c a n t w ith th e same
number o f s p e c ie s .
However, t h e d a ta i n T ab le 7 shows t h a t when th e mean
r a t i o s o f L e b is te s (No. 14) and G ira rd in u s (No. 17) a r e compared th e y d i f ­
f e r s ig n ific a n tly .
H ence, t h e h e t ero chromosomes i n L e b is te s and t h e X
chromosomes i n G ira rd in u s a r e p ro b a b ly n o t a l i k e and i t i s n o t p e r m is s ib le
| t o group th e s e sp e c ie s to g e th e r .
TABLE 7
S p e c ie s
15
15
18
0 .0 0 0
4
3-510
18
4
V9
S p e c ie s
0 .0 0 0
3-510
1
3-510
1
3 .5 1 0
8
0 .1 5 7
---------
-
---------
8
s p e c ie s
0 .1 5 7
14
---------
14
17
3 .720
17
3.720
—
---------
---------
: Graph 18C shows t h a t t h e r e i s more d if f e r e n c e i n s iz e between* t h e X components
* i n G ir a rd in u s (No. 1 7 ) th a n betw een th e X components o f any o f th e o th e r
j s p e c ie s w ith compound h e t erochrom osom es.
!
The mean o f t h e r a t i o betw een th e X chromosomes i n P o e c ilio p s is
in f a n s (No. -4.) i s s i g n i f i c a n t l y d i f f e r e n t from th e means o f f iv e o th e r sp e­
c ie s .
T h is i s a ls o t r u e f o r M o llie n is ia l a t i p i n n a (No. 1 8 ), w ith compound
h et e ro chromosomes, and f o r H e te ra n d ria form osa (No. 1 5 ), w ith a s in g le p a i r
o f heterochrom osom es (T ab le 4 ) (G raph 18A).
P o e c il io p s is cannot be grouped
w ith M o llie n is ia - a n d H e te r a n d r ia , however, b ecau se t h e t e s t s betw een th e
fo rm e r s p e c ie s and t h e two l a t t e r ones a r e s i g n i f i c a n t (T a b le 7) •
M o llie n i­
s i a (No. 18) and H e te r a n d ria (No. 15) can c e r t a i n l y be grouped to g e th e r
f o r , a c c o rd in g t o t h e d a ta , t h e X components i n M o llie n is ia a r e e x a c tly
l i k e t h e two h et ero chromosomes i n H e te r a n d ria .
R eferen ce t o T ab le 3 shows
t h e mean r a t i o s and t h e s ta n d a r d e r r o r s t o be th e same f o r th e s e two form s,
and r e f e r e n c e t o T ab le 7 shows, o f c o u rs e , t h a t th e d if f e r e n c e betw een
t h e i r mean r a t i o s i s z e r o .
A ccording t o t h e r e s u l t s o f t h e s t a t i s t i c a l
a n a l y s i s , t h e X chromosomes i n M o llie n is ia may be s l i g h t l y d i f f e r e n t i n
s i z e , s in c e t h e d i f f e r e n c e betw een them seems g r e a t e r th a n th e d if f e r e n c e
betw een th e chromosomes i n P la ty p o e c ilu s v a r i a t u s (No. 5 ) (G raph 18C).
How-
! e v e r , when M o l l i e n i s i a was t e s t e d w ith P o e c i l i o p s i s , th e r e s u l t o f th e
;; t e s t was s i g n i f i c a n t (T a b le 6 ) , so t h a t t h e d if f e r e n c e betw een th e X ch ro —
I mosomes i n M o ll i e n i s i a i s p ro b a b ly n o t a s l a r g e as th e d if f e r e n c e betw een
th o s e i n P o e c i l i o p s i s .
The means o f t h e r a t i o s betw een th e X chromosomes o f P la ty p o e c ilu s
; v a r i a t u s (No. 5) d i f f e r s i g n i f i c a n t l y from t h e means o f t h r e e o th e r spe­
c ie s (T a b le 4)*
I n s p e c tio n o f Graph 18C shows P la ty p o e c ilu s (No. 5) t o
| have t e s t e d s i g n i f i c a n t l y w ith few er s p e c ie s th a n any o f t h e o th e r s p e c ie s
w ith compound X e le m e n ts.
Hence, i t seems p ro b a b le t h a t t h e X components
i
a r e o f t h e same s i z e .
I n s p e c tio n o f Graph ISA, however, shows P la ty p o e c ilu s
i
. v a r i a t u s (n o . 5) t o be i n t h e second g ro u p .
T ab le 6 shows t h a t th e mean
r a t i o i n P la ty p o e c ilu s v a r i a t u s does n o t d i f f e r s i g n i f i c a n t l y from t h e
means o f t h e o th e r s p e c ie s w ith in t h i s second gro u p .
Ju d g in g from t h e
p o s i t i o n o f P la ty p o e c ilu s i n Graph ISA, one may conclude t h a t t h e X ch ro ­
mosomes may be v e ry s l i g h t l y d i f f e r e n t i n s i z e .
d.
C o r r e la tio n o f t h e t t e s t w ith th e r e s u l t o f s t a t i s t i c a l
tr e a tm e n t o f r a t i o s .
I n G ira rd in u s m e t a l l i c u s , th e r e s u l t o f t h e t t e s t was s i g n i f i ­
c a n t and t h e t e n t a t i v e c o n c lu s io n was t h a t t h e Y chromosome may be l a r g e r
th a n b o th o f t h e X chromosomes o r s i m i l a r i n s iz e t o one o f them .
Analy­
s i s o f th e r a t i o s showed t h a t t h e d i f f e r e n c e s i n s iz e betw een t h e X com­
p o n e n ts i s p ro b a b ly q u i t e l a r g e .
I f t h e r e i s q u i te a d if f e r e n c e betw een
th e two X chromosomes, and th e s in g le Y i s s im il a r i n s iz e t o one o f them ,
one w ould e x p e c t a h ig h ly s i g n i f i c a n t d if f e r e n c e betw een t h e means o f th e
two X chromosomes and t h e s in g l e m easurem ent.
A c tu a lly t h e t v a lu e was n o t
v e r y f a r o v e r th e v a lu e f o r t a t th e 1 p e r c e n t p o in t.
T h e re fo re , i t seems
7-
' m ost l i k e l y t h a t t h e t h r e e chromosomes a r e o f d i f f e r e n t s i z e s .
;
The t t e s t s f o r P o e c i l i o p s i s in f a n s and M o lH e n is ia l a t i p i n n a
I w ere h ig h ly s i g n i f i c a n t , b e in g w e ll o v e r t h e 1 p e r ce n t p o in t.
The g e n e r a l
; c o n c lu s io n was t h a t Y may be l a r g e r th a n one o r b o th o f th e X chromosomes.
A n a ly s is o f t h e r a t i o s showed t h e s iz e d if f e r e n c e s betw een th e X components
i
i
j i n e i t h e r s p e c ie s t o be s m a ll.
However, t h e r e i s a s l i g h t l y g r e a t e r d i f -
i f e re n c e b etw een t h e X chromosomes i n P o e c il io p s is th a n betw een th o s e i n
; M o ll i e n i s i a .
S in c e th e t t e s t v a lu e i s h ig h ly s i g n i f i c a n t , and s in c e th e
| d i f f e r e n c e s betw een t h e X com ponents a r e s m a ll, t h e chances a r e t h a t th e
Y chromosome i s l a r g e r th a n e i t h e r o f th e X com ponents.
The t t e s t f o r P la ty p o e c ilu s v a r i a t u s was not s i g n i f i c a n t b u t no
c o n c lu s io n s c o u ld be draw n.
S t a t i s t i c a l tr e a tm e n t o f t h e r a t i o s betw een
th e X com ponents showed them t o be a l i k e o r n e a r ly s o .
Thus, when th e r e ­
s u l t s o f b o th t e s t s a r e c o n s id e re d , i t seems p ro b a b le t h a t a l l t h r e e h e te ro ­
chromosomes t e n d t o be o f t h e same s iz e .
C.
P o e c i l i s t e s p le u r o s p i l u s (G u en th er) w ith f o u r heterochrom osom es.
1.
C yfcological O b s e rv a tio n s .
D u rin g t h e e a r l i e r p a r t o f th e grow th p e r io d th e germ c e l l n u c le i
c o n ta in f o u r compact b o d ie s w hich may be h e te ro p y c n o tic sex chromosomes.
L a te r s ta g e s show two su ch b o d ie s , one o f them sm a ll and th e second v e ry
la rg e .
Ju d g in g from t h e s iz e o f t h e second body, i t may be t r i p a r t i t e
and r e p r e s e n t t h r e e c l o s e l y a s s o c ia te d chromosomes*
However, t h e m a te r ia l
was d i f f e r e n t i a l l y s t a i n e d f o r o b s e rv a tio n s upon th e h e t ero c h r omo somes
d u rin g t h e p rim a ry sp e rm a to c y te d i v i s i o n an d , u n f o r tu n a te ly , th e e x a c t c h a r­
a c t e r o f t h e l a r g e n u c le o lu s p r e s e n t i n t h e n u c le i d u rin g t h e l a t e r p a r t o f
t h e g ro w th p e r io d c o u ld n o t be d e te rm in e d .
P resu m ab ly t h e d e f i n i t i v e chromosomes a r i s e from a c o n d e n sa tio n
o f sp irem e th r e a d s i n t h e d i f f u s e s ta g e .
D uring th e p rim a ry sp erm ato cy te
d i v i s i o n t h e autosom es a r e a rra n g e d upon t h e s p in d le , w ith th e h e te ro c h ro ­
mosomes a t i t s p e r ip h e r y a s s o c i a te d i n such a manner t h a t th e y form ed a
v e ry l a r g e compact body a tta c h e d t o th e r e s t o f t h e chromosomes by means
o f a s p in d le f i b e r ( F ig . IB ) .
One o f th e h e t ero chromosomes s e p a ra te d from
th e " t e t r a d " s l i g h t l y i n advance o f t h e o th e r t h r e e ( F ig . X I).
I n a s h o rt
tim e , how ever, t h e t r i a d b ro k e up i n t o t h r e e
p o r ti o n s , so
t h a t fo u r ch ro ­
mosomes c o u ld be o b se rv e d on t h e edge o f th e
e q u a t o r ia l p l a t e ( F ig .
4 2 ).
M o rp h o lo g ic a lly t h e h e t e ro chromosomes were i n th e form o f s h o r t r o d s , w hich
i n m ost c a s e s d id n o t a p p e a r double ( F ig . 41)*
a p p e a re d t o be s m a lle r th a n one o f t h e t h r e e
The s in g le Y chromosome
X components
and
p o s s ib ly
s i m i l a r i n s i z e t o t h e o t h e r two ( F ig . 6B ).
Anaphase i n t h e h e t e ro chromosome complex was p r e c o c io u s , w ith
t h r e e chromosomes p a s s in g t o one p o le and one t o t h e o th e r ( F ig . 68 ) .
As
• i n o th e r s p e c i e s , t h e h e t erochromosomes re a c h e d th e p o le b e fo re autosom al
d iv i s i o n o c c u rre d .
t h e s p in d l e .
J u s t p r i o r t o d i v i s i o n th e autosom es s p re a d out upon
P o la r view s o f t h i s s ta g e , i f c e l l s a r e s e c tio n e d p a r a l l e l
t o t h e l o n g i t u d i n a l a x is o f t h e s p in d le , show one o r t h r e e heterochrom osom es
i s o l a t e d from t h e c e n t r a l group ( F ig s . 91, 9 2 ).
T hus, e x cep t f o r t h e p r e ­
sence o f t h r e e com ponents i n t h e X complex in s te a d o f tw o, th e b e h a v io r o f
th e s e chromosomes i n P o e c i l i s t e s c lo s e ly p a r a l l e l e d th e b e h a v io r o f th o s e
i n s p e c ie s w ith t h r e e h e t e ro chromosome s .
2.
S t a t i s t i c a l A n a ly s is
a . G raph o f t h e M easurem ents
S in c e t h e r e w ere f o u r h et ero chromosomes i n each c e l l t h e r e were
200 m easurem ents i n s t e a d o f t h e u s u a l 100.
The g rap h o f t h i s sample ap­
p e a rs t o be b im o d a l, w ith one o f th e modes co m p risin g about t h r e e - f o u r t h s
o f t h e a r e a o f t h e cu rv e (G raph 2 3 ) .
Thus from in s p e c tio n i t would seem
t h a t t h r e e o f t h e f o u r chromosomes a r e o f s i m i l a r s i z e .
b*
S t a t i s t i c a l a n a l y s is o f d if f e r e n c e s betw een th e s in g le Y
chromosome and t h e mean o f t h e t h r e e m easurem ents o f th e X com ponents.
When t h e s in g l e m easurem ent was compared t o t h e mean o f th e t h r e e ,
a v a lu e f o r t o f 0 .7 5 0 was o b ta in e d .
As a r u l e , b ecause t h i s v a lu e o f t
i s much lo w er th a n t h e v a lu e o f t c o rre s p o n d in g t o th e 1 p e r c e n t p o in t i n
t h e t a b l e s , one may co n clu d e t h a t th e d if f e r e n c e betw een th e s in g le mea­
surem ent and t h e means o f t h e o th e r t h r e e does n o t d i f f e r s i g n i f i c a n t l y
from z e ro an d , t h e r e f o r e , t h e p r o b a b i l i t y t h a t a l l th e m easurem ents were
ta k e n a t random from t h e same p o p u la tio n i s v e ry h ig h .
I n r e a l i t y , s in c e
one m easurem ent was compared t o th e mean o f t h r e e o th e r s , one may conclude
t h a t t h e Y chromosome i s n o t v e r y d i f f e r e n t i n s iz e from one o r more o f th e
X com ponents f o r i t i s q u i t e p o s s ib le f o r t h r e e v a lu e s t o d i f f e r from one
a n o th e r and have a mean w hich i s e q u a l t o a f o u r t h v a lu e .
F or in s ta n c e ,
i f a s in g l e chromosome m easured 3 m ic ra and t h e mean o f th e m easurem ents
o f t h r e e o th e r chromosomes e q u a lle d 3 m ic ra , any s t a t i s t i c a l t e s t com paring
th e mean 3 m ic ra t o t h e m easurem ent 3 m ic ra would most l i k e l y g iv e a t
v a lu e w hich i s n o t s i g n i f i c a n t .
However, th e th r e e chromosomes whose mea­
surem en ts gave a mean o f 3 m ic ra m ight have th e s iz e s 2 m ic ra , 2 m ic ra , and
5 m ic ra and th u s a c t u a l l y d i f f e r i n s iz e from th e chromosome m easuring 3
m ic ra .
T h u s, f o r t h e t t e s t t o be o f any v a lu e , som ething must be known
ab o u t t h e s i z e r e l a t i o n s h i p s betw een t h e t h r e e chromosomes o f th e X complex.
c.
S t a t i s t i c a l a n a l y s is o f th e r a t i o s betw een th e t h r e e X components
The mean r a t i o f o r t h e f i f t y av e ra g e r a t i o s o f t h e m easurem ents
made f o r P o e c i l i s t e s was 1 .0 8 5 and t h e s ta n d a rd e r r o r
0 .0 0 9 .
T his mean
when t e s t e d a g a in s t t h e means o f n in e te e n s p e c ie s was s i g n i f i c a n t l y d i f ­
f e r e n t from s i x o f them (T a b le 4 ) .
I n Graph 18A, P o e c i l i s t e s i s grouped
w ith L in d a n i g r o f a s c i a t a (No. 8 ) , from w hich i t does n o t seem t o d i f f e r
s i g n i f i c a n t l y (T a b le 7 ) .
T hus, c o n s id e rin g t h e p o s iti o n o f P o e c i l i s t e s i n
Graph 18A, one may t e n t a t i v e l y conclude t h a t t h e t h r e e chromosomes o f th e
X com plex a r e n o t a l l a l i k e a lth o u g h t h e d if f e r e n c e s betw een them a re not
as g r e a t a s t h e d i f f e r e n c e s betw een t h e chromosomes o f L e b is te s (No. 1 4 ),
P seu d o x ip h o p h o ru s (No. 2 ) , and G ira rd in u s (No. 1 7 ).
When th e X complex of
P o e c i l i s t e s i s compared t o th o s e i n th e o th e r s p e c ie s e x h i b iti n g compound
heterochrom osom es, o n ly t h e X chromosomes i n G ira rd in u s (No. 17) show a
g r e a t e r d e g re e o f d i f f e r e n c e (G raph 18C ).
However, t h e d if f e r e n c e s be­
tw een t h e X chromosomes o f G ira rd in u s seem t o be o f much g r e a t e r m agnitude
th a n t h o s e betw een t h e X chromosomes o f P o e c i l i s t e s .
Thus i t seems p ro ­
b a b le t h a t t h e X chromosomes i n P o e c i l i s t e s p le u r o s p llu s d i f f e r o n ly s l i g h t l y
from one a n o th e r .
d.
C o r r e la tio n o f t h e t t e s t w ith th e r e s u l t s o f s t a t i s t i c a l
tr e a tm e n t o f t h e r a t i o s .
One may r e c a l l t h a t t h e r e s u l t o f th e t t e s t p e r m itte d o n ly a
v e ry g e n e r a l c o n c lu s io n , nam ely, t h a t t h e s in g le Y chromosomes may be o n ly
s l i g h t l y d i f f e r e n t i n s i z e from th o s e o f th e X com plex.
A n aly sis o f t h e
r a t i o s showed t h a t t h e r e may be a s l i g h t d if f e r e n c e betw een th e X chromo­
somes o f P o e c i l i s t e s .
I f t h i s be t r u e , th e n th e Y chromosome i s p ro b a b ly
s i m i l a r i n s iz e t o one o f t h e chromosomes o f th e X complex, f o r a c c o rd in g
t o t h e r e s u l t s o f t h e t e s t s betw een th e X chromosomes, th e v a lu e s w hich
c o n t r ib u t e t o t h e mean u se d i n th e t t e s t cannot be to o d i f f e r e n t from one
a n o th e r o r t h e d i f f e r e n c e s betw een th e s ta n d a rd e r r o r s o f th e mean betw een
P o e c i l i s t e s and t h e o th e r s p e c ie s would be s ig n i f i c a n t i n a g r e a te r number
of cases.
V.
A.
SUMMARY OF RESULTS
Twenty s p e c ie s o f p o e c i l i i d f is h e s were s tu d ie d .
c i e s had one p a i r o f h e t e ro chromosome s .
heterochrom osom es.
F if t e e n o f t h e spe­
F iv e o f th e s p e c ie s had compound
F our o f t h e f i v e p o s se s se d a s in g le Y chromosome and
two X chromosomes w h ile t h e re m a in in g s p e c ie s had a s in g le Y chromosome
opposed by t h r e e X chromosomes.
1.
Those s p e c ie s w ith a s in g l e p a i r o f h et ero chromosomes:
P seu d o x ip h o p h o ru s b im a c u la tu s G uenther
X iphophorus h e l l e r i i H eckel
Gambusia panuco panuco Hubbs
Gambusia a f f i n i s h o lb ro o k ii G ira rd
L im ia n i g r o f a s c i a t a Regan
L im ia v i t t a t a G uichenot
Q u in tan a a t r i z o n a Kubbs
Moll t e n i s i a sphenops C u v ier and V ale n c ie n n e s
M o ll i e n i s i a p e te n e n s is Hubbs
G l a r i d i chb hys f a l c a t u s Eigenmann
L e b is te s r e t i c u l a t u s P e te r s
H e te r a n d ria form osa A g assiz
M-i c r o p o e c i l i a b r a n n e r i Eigenmann
B ra ch y rh ap h is e p is c o p i S te in d a c h n e r
P la ty p o e c ilu s m ac u la tu s G uenther
2.
Those s p e c ie s w ith compound heterochrom osom es
a.
S p e c ie s w ith t h r e e heterochrom osom es:
P l a ty p o e c ilu s v a r i a t u s Meek
G ira rd in u s m e t a l i i c u s Poey
P o e c i l i o p s i s i n f a n s Hubbs
M o ll i e n i s i a l a t i p i n n a LeSueur
b.
S p e c ie s v d th f o u r heterochrom osom es:
P o e c i l i s t e s p le u r o s p ilu s G uenther
B.
Summary o f c y t o l o g i c a l o b s e rv a tio n s upon th e b e h a v io r o f h e te ro c h ro ­
mosomes
1.
T h e re i s e v id e n c e t h a t th e h et e ro chromosomes become h e te ro p y c -
n o t i c d u r in g t h e grow th p e r io d .
I n s p e c ie s w ith one p a i r o f h e t e ro chromo­
somes, two s in g l e com pact, d e n s e ly s t a i n i n g b o d ie s a r e o b serv ed i n t h e
n u c le i o f germ c e l l s i n t h e e a r l y grow th p e r io d .
L a te r , depending upon
w h eth er t h e r e a r e tw o , t h r e e o r f o u r heterochrom osom es i n a g iv e n s p e c ie s ,
t h e s e b o d ie s become a s s o c i a t e d t o form la r g e d o u b le, t r i p a r t i t e o r q u a d ri­
p a r t i t e chromosome n u c l e o l i .
H e tero p y cn o sis i s n o t o f th e extrem e ty p e
c h a r a c t e r iz e d by co m plete i s o l a t i o n o f t h e chromosomes w ith in a s e p a ra te
v e s ic le .
2.
The h e t e ro chromosomes a r e s t i l l a s s o c ia te d when th e y a r e f i r s t
o b serv ed d u r in g t h e p rim a ry sp e rm ato cy te d i v is io n and th e y la g b eh in d th e
autosom es i n becom ing a rra n g e d upon t h e s p in d le .
At t h i s tim e th e p o s i­
t i o n o f t h e s e chromosomes upon t h e e q u a t o r i a l p l a t e i s alm ost th e same i n
ea c h c e l l i n e v e ry s p e c i e s .
They l i e a s h o rt d is ta n c e away from th e a u to ­
somes m assed upon t h e e q u a t o r i a l p l a t e , b u t a r e co n n ected t o t h e c e n t r a l
group by a s e p a r a te s p in d le f i b e r .
3.
I n t h e p rim a ry sp e rm a to c y te d i v i s i o n , th e a s s o c ia te d h e te r o c h ro -
mosomes s e p a r a t e and p a s s u n d iv id e d t o th e p o le s .
Hence th e h e te r o k in e t ic
( r e d u c t i o n a l ) d i v i s i o n o c c u rs b e f o re th e e q u a tio n a l d iv is io n .
4-
D u rin g h e t e r o k i n e s i s t h e h e t ero chromosomes p reced e th e autosom es
t o t h e p o le s .
W ith r e s p e c t t o t h e s e chromosomes, anaphase i s p re c o c io u s
f o r t h e heterochrom osom es re a c h t h e p o le s o f th e s p in d le b e fo re th e a u to ­
somes d iv id e .
5*
I n t h e f i f t e e n s p e c ie s w ith one p a i r o f h e t ero chromosomes, one
chromosome p a s s e s t o one p o le and th e o th e r t o t h e o p p o s ite p o le .
I n th e
f o u r s p e c ie s w ith t h r e e h e t e ro chromosomes, a s in g l e chromosome p a s s e s t o
one p o le and two t o t h e o p p o s ite p o le .
I n a s p e c ie s p o s s e s s in g fo u r
heterochrom osom es, a s in g le chromosome a g a in p a s s e s t o one p o le and t h r e e
t o t h e o p p o s ite p o le .
6.
No la g g in g o r p r e c e s s io n was o b serv ed i n t h e seco n d ary sperm ato­
c y te d i v i s i o n .
P resum ably t h e heterochrom osom es d iv id e e q u a tio n a lly and
p a s s t o t h e p o le s a lo n g w ith t h e autosom es.
C.
S iz e d i f f e r e n c e s and m orphology o f th e h et ero chromosomes
1.
lik e .
The h e t e ro chromosomes i n a l l s p e c ie s were s h o r t, com pact, and ro d I n some o f t h e s p e c ie s a m edian c o n s tr i c t i o n gave th e r o d - l i k e
heterochrom osom es a s l i g h t l y du m b-bell l i k e form .
a.
Those s p e c ie s i n w hich no m edian c o n s t r i c t i o n was o b serv ed :
P seu d o x ip h o p h o ru s b im a c u la tu s
Lim ia n i g r o f a s c i a t a
L im ia v i t t a t a
M o ll i e n i s i a sphenops
M o ll i e n i s i a l a t i p i n n a
M o ll i e n i s i a p e te n e n s is
G la ry d i c hb hy s f a l c a t u s
Gambusia a f f i n i s h o lb ro o k ii
Gambusia panuco panuco
M ic r o p o e c ilia b r a n n e r i
P la ty p o e c ilu s v a r i a t u s
P o e c ilio p s is in fa n s
P o e c i l i s t e s p le u r o s p ilu s
G ira rd in u s m e ta llic u a
b*
Those s p e c ie s i n w hich th e h e t ero chromosomes p o s s e s s e d a
m edian c o n s t r i c t i o n :
L e b is te s r e t i c u l a t u s
H e te ra n d ria form osa
Q u in tan a a t r iz o n a
Bra c hyrhap h i s e p is c o p i
X iphophorus h e l l e r i
P la ty p o e c ilu s m acu latu s
2.
I n some s p e c ie s d if f e r e n c e s betw een th e h e t ero chromosomes were
o b s e rv a b le , and i n o th e r s th e y were n o t:
a*
S p e c ie s i n w hich t h e chromosomes were o b s e rv a b ly d i f f e r e n t :
L e b is te s r e t i c u l a t u s
P seud o x ip h o p h o ru s b im a c u la tu s
L im ia n ig r o f a s c i a t a
G ira rd in u s met a l i i cus (The Y and t h e two X chromosomes may
be o f t h r e e d i f f e r e n t s iz e s )
P o e c ilio p s is in fa n s (Y l a r g e r th a n th e two X chromosomes)
M o l l i e n i s i a l a t i p i n n a (Y l a r g e r th a n th e two X chromosomes)
P o e c i l i s t e s p le u r o s p il u s (Y s m a lle r th a n one o f th e t h r e e X
com ponents.
Two o f t h e X chromosomes may be l a r g e r
th a n t h e t h i r d ) ,
b.
S p e c ie s i n w hich s iz e r e l a t i o n s h i p s betw een th e chromosomes
c o u ld n o t be d e te rm in e d c y t o l o g i c a lly :
Het e r a n d r i a form osa
Q u in tan a a t r iz o n a
B ra c h y rh a p h is e p is c o p i
X iphophorus h e l l e r i i
P la ty p o e c ilu s m a cu latu s
P la ty p o e c ilu s v a r i a t u s (The Y and th e two X chromosomes)
Lim ia v i t t a t a
M o ll i e n i s i a sphenops
M o ll i e n i s i a p e te n e n s is
M o ll i e n i s i a l a t i p i n n a (The two X chromosomes)
G la ry d ic b th y s f a l c a t u s
Gambusia a f f i n i s h o lb ro o k ii
Gambusia panuco panuco
M ic r o p o e c ilia b r a n n e r i
P o e c i l i o p s i s in f a n s (The two X chromosomes)
P o e c i l i s t e s p l e u r o s p ilu s (Two o f th e X chromosomes)
3.
S e v e ra l ty p e s o f fre q u e n c y d i s t r i b u t i o n s w ere o b ta in e d from th e
m easurem ents o f heterochrom osom es.
a.
One ty p e o f cu rv e was t a l l , narrow and peaked w ith a p o s s i b le
skew ness t o t h e r i g h t :
83 :
|
P s eu d o x ip hop ho ru s b im a c u la tu s
i
M o l l i e n i s i a sphenops
I
Gambusia panuco panuco
i
M ic r o p o e c ilia b r a n n e r i
;
b.
The c u rv e s f o r s e v e r a l s p e c ie s were not ex tre m e ly t a l l but
; were somewhat p eak e d .
The d i s t r i b u t i o n upon e i t h e r s id e o f th e modal c la s s
t
te n d e d t o be more o r l e s s sy m m etrical:
P l a ty p o e c ilu s m a c u la tu s
L im ia v i t t a t a
M o ll i e n i s i a p e te n e n s is
G la ry d i ch t hys f a l c a t u s
H e te r a n d ria form osa
Q u in ta n a a t r iz o n a
P la ty p o e c ilu s v a r i a t u s
c.
A n o th er c l a s s o f c u rv es showed v a r io u s d eg rees o f b im o d a lity :
L e b is te s r e t i c u l a t u s
L im ia n ig r o f a s c i a t a
X iphophorns h e l l e r i i
Gambusia a f f i n i s h o lb ro o k ii
B ra eh y rh a p h is e p is c o p i
P o e c i l i o p s i s in f a n s
M o llie n is ia la tip in n a
P o e c i l i s t e s p le u r o s p ilu s
d.
The cu rv e o f G ira rd in u s met a l i i c u s , a s p e c ie s w ith t h r e e
heterochrom osom es, was tr im o d a l.
4.
R e s u lts o f s t a t i s t i c a l a n a ly s is o f m easurem ents from s p e c ie s w ith
two h e t erochrom osom es.
a.
T h ree s p e c ie s have chromosomes w hich, a c c o rd in g t o s t a t i s ­
t i c a l a n a l y s i s , a r e d i f f e r e n t i n le n g th :
L e b is te s r e t i c u l a t u s
Ps eudoxiphophorus b im a c u la tu s
L im ia v i t t a t a
b.
same s i z e .
S ix s p e c ie s have heterochrom osom es w hich a r e p ro b a b ly th e
T hese showed t h e few est number o f s i g n i f i c a n t t e s t s when t e s t e d
w ith a l l o f t h e o th e r s p e c ie s and d id n o t t e s t s i g n i f i c a n t l y w ith one a n o th e r .
X iphophorus h e l l e r i i
Gambusia panuco panuco
M o ll i e n i s i a p e te n e n s is
M ic r o p o e c ilia b r a n n e r i
B raeh y r h a p h is e p is c o p i
P la ty p o e c ilu s m a cu latu s
c.
A t h i r d group gave s i g n i f i c a n t t e s t s w ith o n ly one more spe­
c i e s t h a n t h e above g ro u p .
The s p e c ie s i n t h i s t h i r d group d id not d i f f e r
s i g n i f i c a n t l y from one a n o th e r .
The chromosomes o f th e s e s p e c ie s may d i f f e r
v e r y s l i g h t l y from one a n o th e r .
L im ia v i t t a t a
M o ll i e n i s i a sphenops
G la ry d ic h th y s f a l c a t u s
Gambusia a f f i n i s h o lb ro o k ii
d.
Two s p e c i e s , Q u in tan a a tr iz o n a and H e te ra n d ria fo rm o sa, were
i n te r m e d ia te betw een t h e s p e c ie s w hich were h ig h ly s i g n i f i c a n t and th o s e
w hich w ere n o t .
Thus t h e i r chromosomes d i f f e r i n s iz e more th a n th o s e o f
t h e t e n s p e c ie s i n t h e l a s t two groups d e s c r ib e d , and n o t a s much a s t h e
t h r e e s p e c ie s i n t h e group w hich showed t h e g r e a t e s t number o f s i g n i f i c a n t
te s ts .
5«
R e s u lts o f s t a t i s t i c a l a n a l y s is o f m easurem ents from s p e c ie s w ith
compound heterochrom osom es.
A t t e s t t e s t e d th e s i z e r e l a t i o n s h i p betw een th e Y chromosomes
and t h o s e o f t h e X com plex, w h ile t e s t s o f d if f e r e n c e s betw een t h e mean o f
t h e r a t i o s t e s t e d t h e s i z e r e l a t i o n s h i p s betw een th e X chromosomes.
S iz e
d i f f e r e n c e s w ere e s t a b l i s h e d by c o r r e l a t i n g t h e r e s u l t s o f t h e two t e s t s .
a.
The t h r e e heterochrom osom es o f G ira rd in u s met a l i i cus a r e p ro ­
b a b ly o f t h r e e d i f f e r e n t s i z e s .
b.
The t h r e e heterochrom osom es o f P la ty p o e c ilu s v a r i a t u s a r e
p ro b a b ly a l l t h e same s i z e .
c.
In M o ll i e n i s i a l a t i p i n n a and i n P o e c ilio p s is in f a n s t h e Y
chromosomes and t h e X chromosomes a r e p ro b a b ly t h e same s i z e .
d.
I n P o e c i l i s t e s p le u r o s p ilu s t h e Y chromosome i s p ro b a b ly
s i m i l a r i n s i z e t o a t l e a s t one o f t h e X chromosomes.
The t h r e e X chromo­
somes may d i f f e r s l i g h t l y from one a n o th e r.
V I.
A.
DISCUSSION AND CONCLUSIONS
The p o s s ib le f u n c t io n a l s ig n i f ic a n c e o f t h e h et e r o c h r omo s ome s i n th e
P o e c iliid a e
I n t h e germ c e l l s o f a l l o f th e tw e n ty s p e c ie s o f P o e c il iid a e
s tu d ie d t h e r e w ere chromosomes w hich, because o f t h e i r g e n e r a l b e h a v io r,
c o u ld be c l a s s i f i e d a s h e t ero chromosome s .
F i f t e e n o f th e s p e c ie s p o s se s se d
one p a i r o f heterochrom osom es, f i v e o f th e s p e c ie s had th r e e heterochrom o­
somes and one s p e c ie s had f o u r o f them .
B ecause a l l heterochrom osom es a r e
n o t s e x chromosomes, c r i t e r i a w hich d i s t i n g u i s h t h e h e t ero chromosomes w hich
f u n c tio n a s se x chromosomes from o th e r chromosomes have been e s ta b li s h e d .
One o f t h e m ost c h a r a c t e r i s t i c a s p e c ts o f th e b e h a v io r o f se x
chromosomes i s t h e i r te n d e n c y t o undergo a p ro c e s s o f h e te ro p y c n o s is d u rin g
t h e grow th p e r io d o f t h e a u x o c y te s .
The e x te n t o f h e te ro p y c n o s is v a r ie s
from a n ex trem e ty p e i n w hich t h e s e x chromosomes become condensed and i s o ­
l a t e d i n a d i s t i n c t v e s i c l e a t t h e p e r ip h e r y o f t h e n u c le u s t o a ty p e i n
w hich t h e r e i s c o n d e n s a tio n w ith more o r l e s s i s o l a t i o n , b u t no in c lo s u r e
w ith in a v e s i c l e .
E v id en ce has been p r e s e n te d w hich shows t h a t t h e r e i s a
s tr o n g p o s s i b i l i t y t h a t t h e heterochrom osom es i n t h e P o e c il iid a e a r e i n a
condensed form d u rin g t h e grow th p e r io d and te n d t o become i s o l a t e d n e a r
th e n u c le a r w a ll.
S in c e t h i s b e h a v io r i s v e ry s im i l a r t o th e b e h a v io r d f
se x chromosomes e x h i b i t i n g t h e l e s s extrem e ty p e o f h e te ro p y c n o s is , one
may t e n t a t i v e l y co n clu d e t h a t i n t h e P o e c i lii d a e th e heterochrom osom es go
th ro u g h a p ro c e s s o f h e te ro p y c n o s is d u rin g th e grow th p e r io d o f th e p rim a ry
s p e rm a to c y te s and t h u s , i n t h i s r e s p e c t , behave l i k e sex chromosomes.
A nother c h a r a c t e r i s t i c o f se x chromosomes i s t h a t th e y d iv id e
e q u a t i o n a l l y i n one o f t h e sp e rm a to c y te d iv is io n s and undergo a d i f f e r e n ­
t i a l o r h e t e r o k i n e t i c d i v i s i o n i n t h e o th e r .
The h e t ero chromosomes i n a l l
tw e n ty s p e c ie s o f t h i s group o f to p minnows show ev id en ce o f a d i f f e r e n t i a l
o r h e te ro k in e tic d iv is io n .
D u rin g t h e p rim a ry sp erm ato cy te d i v i s i o n , th e y
a p p e a r upon t h e e q u a t o r i a l p l a t e a s s o c ia te d w ith one a n o th e r t o form a d i­
v a l e n t , t r i v a l e n t o r t e t r a v a l e n t body, depending upon w h eth er th e s p e c ie s
has tw o , t h r e e o r f o u r h e t e ro chromosome s .
D uring th e en su in g p rim a ry s p e r ­
m a to c y te d i v i s i o n th e m u ltiv a le n t body d i s s o c i a t e s i n t o s e p a r a te chromo­
somes w hich p a s s t o o p p o s ite p o le s .
Such b e h a v io r seems v e ry d e f i n i t e l y
t o be t y p i c a l o f t h e h e te r o k in e s e s c h a r a c t e r i s t i c o f sex chromosomes and
hen ce, i n t h i s r e s p e c t , t h e heterochrom osom es o f th e P o e c ili id a e a r e s im i l a r
t o th em .
Sex chromosomes commonly e i t h e r p re c e d e o r su cceed th e autosom es
when p a s s in g t o t h e p o le s i n t h e p rim a ry sp e rm a to c y te d i v i s i o n .
In a l l of
t h e s p e c ie s s tu d i e d , t h e heterochrom osom es p re c e d e d th e autosom es t o th e
p o le s .
As a r u l e , s e x chromosomes w hich show p r e c e s s io n d iv id e about th e
same tim e a s t h e autosom es and p a ss t o th e p o le s o n ly s l i g h t l y i n advance
o f them .
I n t h e h e t e ro chromosomes o f t h e P o e c i l i i d a e , however, d iv is io n
was p r e c o c io u s and p a ssa g e t o t h e p o le s was p r a c t i c a l l y com plete b e fo re
t h e autosom es d iv id e d .
T hus, a g a in , t h e b e h a v io r o f t h e heterochrom osom es
s tu d ie d i s s i m i l a r t o t h a t shown by heterochrom osom es w hich f u n c tio n as
se x chrom osom es.
Sex chromosomes w hich show h e te r o k in e s is d u rin g th e p rim ary s p e r ­
m ato c y te d i v i s i o n o f te n p a s s t o t h e p o le s a s l o n g i t u d i n a l ly d ouble b o d ie s ,
owing t o t h e a p p e ara n ce -of a l o n g i tu d i n a l s p l i t w hich r e p r e s e n ts t h e p la n e
o f t h e e q u a tio n a l d i v i s i o n .
M edian c o n s tr i c t i o n s were o b serv ed upon th e
h e t e ro chromosomes i n s i x o f t h e tw e n ty s p e c ie s .
These may r e p r e s e n t th e
p la n e o f th e e q u a tio n a l d i v i s i o n an d , i f s o , i n t h i s r e s p e c t t h e h e te r o ­
chromosomes o f t h e s i x s p e c ie s a r e s im i l a r m o rp h o lo g ic a lly t o th e sex ch ro ­
mosomes i n o th e r a n im a ls .
I n a g r e a t many c a s e s d u rin g th e p rim ary sp erm ato cy te d iv i s io n
th e p o s i t i o n o f s e x chromosomes upon th e e q u a t o r i a l p l a t e i s alm o st con­
s ta n t.
I n o th e r w ords, t h e p o s i t i o n o f t h e sex chromosomes w ith r e s p e c t
t o t h e p o s i t i o n o f t h e autosom es i s th e same from' c e l l t o c e l l .
I n th e
P o e c i l i i d a e t h i s was t r u e n o t o n ly f o r a l l o f th e p rim a ry sp e rm a to c y te s
o f one s p e c ie s b u t i n a l l o f t h e tw e n ty s p e c ie s , th e heterochrom osom es were
v e ry s i m i l a r i n r e s p e c t t o t h e i r p o s i t i o n a l r e l a t i o n s h i p t o t h e autosom es
upon t h e e q u a t o r i a l p l a t e .
I t i s e v id e n t, th e n , th a t th e beh avior o f th e het ero chromosomes
in t h e s e t e l e o s t s i s remarkably s im ila r t o th e behavior d escrib ed fo r th e
se x chromosomes i n o th er an im a ls.
In view o f t h i s s im ila r it y i t seems q u ite
j u s t i f i a b l e t o conclude th a t th e heterochromosomes in th e to p minnows, as
f a r as c y t o lo g ic a l o b se rv a tio n can determ ine, are analogous t o th e sex chro­
mosomes i n o th e r form s.
Such a c o n c lu s io n i s i n agreem ent w ith th e c o n c lu s io n s made by
some o f t h e c y t o l o g i s t s who have worked upon t e l e o s t e a n germ c e l l s .
( 1 9 2 6 ) fo u n d e v id e n c e f o r a se x chromosome
F oley
i n Umbra l i m i , and B ennington
(1936) t e n t a t i v e l y co n clu d ed t h a t i n B e tta so le n d e n s a p a i r o f chromosomes
w hich la g g e d i n d i v i s i o n and su cceeded t h e autosom es t o th e p o le s r e p r e ­
s e n te d t h e se x chromosomes.
G e is e r, V au p el, and R a ls to n s tu d ie d sperma­
to g e n e s is i n v a r io u s P o e c i l i i d a e .
G e ise r ( I 924) d e s c rib e d la g g in g chromo­
somes i n Gambusia a f f i n i s h o lb r o o k ii but m e re ly su g g e ste d t h a t th e y m ight
be h e t e ro chromosome s .
V aupel ( 1 9 2 9 ) , w orking w ith L e b is te s r e t i c u l a t u s .
and R a ls to n ( 1 9 3 4 ) , w orking upon P la ty p o e c ilu s m acu latu s and X iphophorus
h e l l e r i i » d e s c rib e d chromosomes w hich p reced ed t h e autosom es t o th e p o le s
i n t h e p rim a ry sp e rm a to c y te d i v i s i o n .
They s u g g e ste d t h a t th e chromosomes
o b se rv e d were se x chromosomes.
Most o f th e c y t o lo g is t s stu d yin g th e germ c e l l s o f t e l e o s t s ,
however, have f a i l e d t o fin d any evid en ce f o r sex chromosomes.
The g rea ter
p art o f th e n e g a tiv e ev id en ce has been accumulated through th e stu d y o f
t e l e o s t s o th e r t h a n t h e p o e c i l i i d s .
T here a r e a few s tu d ie s upon th e poe—
c i l i i d s , how ever, i n w hich t h e i n v e s t i g a t o r s f a i l e d t o o b serv e h e te r o chromosomes.
I r i k i ( 1932a) r e p e a te d G e is e r ’s work upon Gambusia and f a i l e d
t o f i n d e v id e n c e f o r heterochrom osom es.
Friedm an and Gordon ( 1934) and
Winge (1 9 2 2 a ), a l l men who a r e p r im a r ily g e n e t i c i s t s , made c y t o lo g ic a l
s tu d i e s upon t h e germ c e l l s o f P la ty p o e c ilu s and L e b is te s .
Gordon and
Friedm an f a i l e d t o c o r r o b o r a te R a ls to n ’ s work upon P la ty p o e c ilu s and Winge
f a i l e d t o c o r r o b o r a te V a u p e l's work upon L e b is te s .
Winge, m oreover, not
o n ly f a i l e d t o f in d t h e heterochrom osom es, b u t found no ev id en ce a t a l l
o f c e l l s i n s ta g e s o f s y n a p s is o r d i a k i n e s i s .
I n t h i s s tu d y some t r o u b l e
was had i n o b ta in in g specim ens o f L e b is te s I n w hich t h e r e was a c t i v e s p e r ­
m a to g e n e s is .
F our o u t o f sev en specim ens had t e s t e s w hich c o n ta in e d p ra c ­
t i c a l l y n o th in g b u t c e l l s i n g o n ia l d iv is i o n s , c e l l s i n th e seco n d ary
sp e rm a to c y te d i v i s i o n , tra n s f o rm in g sp e rm a tid s and m atu re sp erm ato zo a.
It
i s p o s s i b l e t h a t Winge o b serv ed s e c tio n s o f t e s t e s w hich were v e ry s im il a r
t o t h e ones j u s t d e s c r ib e d .
I f su ch were th e c a s e , he would f in d p r a c t i ­
c a l l y no s y n a p s is and no ev id en ce f o r heterochrom osom es, s in c e i n t h e se ­
co n d ary sp e rm a to c y te d i v i s i o n t h e h e t ero chromosomes a p p ear t o behave l i k e
t h e au to so m es.
W hile t h e c y t o l o g i c a l e v id e n c e f o r se x chromosomes i n th e t e l e o s t s
i s c o n t r a d i c t o r y , t h i s i s n o t t r u e o f th e g e n e tic a l e v id e n c e .
I n th o s e
s p e c ie s o f P o e c i l i i d a e i n w hich in h e r ita n c e o f c o lo r p a t t e r n s has been
e x t e n s iv e ly s tu d ie d , t h e r e i s much ev id en ce f o r se x lin k a g e .
Winge (1927)
fo u n d t h a t s e v e n te e n out o f e ig h te e n genes a s s o c ia te d w ith th e d e te rm in a ­
t i o n o f c o lo r p a t t e r n s i n L e b is te s were s e x - lin k e d .
Gordon (1927) and
B ellam y (1922 and 1928) showed t h a t th e f a c t o r s f o r re d body c o lo r , s p o t-
"ting and a l l - o v e r b la c k body c o lo r were sex—lin k e d .
T here i s a ls o some
i n d i c a t i o n o f s e x lin k a g e i n t h e i n h e r ita n c e o f o ran g e—re d body c o lo r and
b la c k s p o ts i n X iphophorns montezumae.
T hus, i n a d d itio n t o th e c y t© lo g i­
c a l e v id e n c e b e h in d t h e c o n c lu s io n t h a t th e heterochrom osom es i n th e s e f i s h
a r e se x chromosomes, t h e r e I s g e n e t i c a l ev id e n c e f o r some o f th e s p e c ie s
t h a t a t l e a s t one p a i r o f chromosomes p ro b a b ly f u n c tio n s a s a p a r t o f t h e
se x d e te rm in in g m echanism .
B.
D is c u s s io n o f t h e ty p e o f sex d e te rm in in g mechanism p r e s e n t i n t h e
P o e c iliid a e
S p e c ie s w ith one p a i r o f se x chromosomes:
B ecause a s i n g l e u n p a ire d sex chromosome
was n o t o b serv ed In
any o f t h e m ale to p minnows, i t i s q u ite c e r t a i n t h a t none o f them have
t h e P r o te n o r XX -X0 ty p e o f se x d e te r m in a tio n .
The m a jo r ity o f th e tw e n ty
s p e c ie s p o s s e s s e d one p a i r o f se x chromosomes and th u s may have e i t h e r th e
D ro so p h ila XX -XY ty p e o f s e x i n h e r ita n c e o r th e A braxas ZZ - 2W ty p e .
T h ree o f t h e s p e c ie s s tu d ie d a p p e a r t o have t h e D ro so p h ila ty p e
o f s e x d e te r m in a tio n f o r a l l l i n e s o f ev id e n c e p o in t t o su ch a c o n c lu s io n .
?*fhile i t i s t h e o r e t i c a l l y p o s s ib le t h a t a s p e c ie s w ith m o rp h o lo g ic a lly
d i s t i n c t s e x chromosomes i n t h e m ale may be p h y s io lo g ic a lly o f th e ZZ - ZW
ty p e , i t i s n o t p r o b a b le .
As f a r a s co u ld be a s c e r ta in e d , t h e r e i s no
r e c o r d o f a s p e c ie s i n w hich th e se x chromosomes i n b o th sex es a r e h e te r o m orphic
or
o f one I n w hich se x chromosomes o f th e X and Y ty p e a re gene­
t i c a l l y a lik e .
1.
L e b is te s r e t i c u l a t u s
p o s s e s s e s a p a i r o f se x chromosomes
w hich a r e d i f f e r e n t enough i n s iz e f o r t h e i r d if f e r e n c e s t o be o b s e rv a b le
i n s p i t e o f t h e f a c t o r o f s e c t io n in g .
The d i s t r i b u t i o n o f t h e m easurem ents
o f t h e s e x chromosomes was m ark ed ly b im o d al, s u g g e s tin g t h a t t h e m easure­
m ents w ere made from chromosomes w hich form ed a h e tero g en eo u s p o p u la tio n ,
i.
e . w ere o f d i f f e r e n t s i z e .
S t a t i s t i c a l a n a ly s is o f th e d a ta s u b s t a n t i a t e d
th e e v id e n c e o b ta in e d by c y t o l o g ic a l o b s e rv a tio n and by in s p e c ti o n o f th e
d i s t r i b u t i o n cu rv e o f t h e m easurem ents.
F o r t h e p a s t f i f t e e n o r more y e a r s Winge has been a c cu m u latin g
g e n e tic d a ta upon L e b is t e s .
A n a ly s is o f r a t i o s o b ta in e d i n s tu d y in g th e
i n h e r i t a n c e o f se x l i n k e d f a c t o r s has l e d Winge t o co n clu d e t h a t L e b is te s
has an XX - XY ty p e o f se x d e te r m in a tio n .
Thus i n t h i s s tu d y , b o th th e
c y t o l o g i c a l o b s e rv a tio n s and t h e m a th e m a tic a l a n a ly s is o f m easurem ents o f
t h e s e x chromosomes a r e i n agreem ent w ith h is c o n c lu s io n .
2.
From t h e r e s u l t s o f c y to l o g ic a l o b s e rv a tio n and s t a t i s t i c a l
a n a l y s is o f d a t a , L im ia n i g r o f a s c i a t a has been shown t o be d ig a m e tic i n
t h e m ale s e x .
The g e n e t i c a l ev id en ce f o r an XX - XY ty p e o f in h e r ita n c e
i s n o t a s c l e a r i n Lim ia a s i n L e b is te s .
B r e id e r , how ever, i n c r o s s in g
L~i mi a n i g r o f a s c i a t a w ith o t h e r <s p e c ie s o f L im ia, came t o th e c o n c lu s io n
t h a t L. n i g r o f a s c i a t a b elo n g ed t o t h a t group o f an im als w ith th e D ro so p h ila
ty p e o f se x d e te r m in a tio n .
3.
I n P seu doxiphophorus b im a c u la tu s t h e s e x chromosomes a re un­
l i k e i n s i z e a n d , h en c e, p ro b a b ly r e p r e s e n t an X and a Y chromosome.
l o g i c a l and s t a t i s t i c a l e v id en ce s u b s t a n t i a t e s t h i s c o n c lu s io n .
Cyto­
As f a r a s
i s known, Ps eudoxip hop h orus has n o t been an a ly z e d g e n e t i c a l l y , so t h a t
t h e r e i s no g e n e tic ev id en ce t o su p p o rt o r oppose t h i s c o n c lu s io n .
4.
T h ere i s no g e n e tic ev id en ce t o a id one i n d e c id in g w hich
ty p e o f se x d e te rm in in g mechanism o c c u rs i n H e te ra n d ria form osa and Quin-
ta h a a t r i z o n a .
From t h e r e s u l t s o f s t a t i s t i c a l a n a ly s is t h e sex chromo­
somes seem t o be somewhat d i f f e r e n t , b e in g in te r m e d ia te i n s iz e betw een
th e chromosomes i n t h e ZZ — ZW and XX — XX g ro u p s.
Cyt © lo g ic a lly a s iz e
d if f e r e n c e betw een t h e p a i r s o f chromosomes i n e i t h e r s p e c ie s i s n o t ob­
s e r v a b le .
P o s s ib ly one may i n f e r t h a t t h e s e x chromosomes d i f f e r i n s iz e
and hence f o llo w t h e D ro so p h ila ty p e o f s e x d e te r m in a tio n .
However, th e
d if f e r e n c e i s not g r e a t enough t o be c y t o l o g i c a l l y a p p a re n t o v er and above
t h e s e c t io n i n g f a c t o r .
A group o f s i x o f th e tw e n ty s p e c ie s o f P o e c i l i i d s ap p e a rs t o
have t h e A braxas ty p e o f se x i n h e r it a n c e .
At l e a s t c y to lo g i c a l o b s e r­
v a ti o n and s t a t i s t i c a l a n a l y s is do n o t show th e sex chromosomes t o be o f
two d i f f e r e n t s i z e s .
I t i s o f c o u rse p o s s ib le f o r two su ch chromosomes t o
be a l i k e i n s iz e and t o be d i f f e r e n t p h y s io l o g ic a lly .
1.
G e n e tic e v id e n c e f o r an A braxas ty p e o f se x in h e r ita n c e has
been c l e a r l y e s t a b l i s h e d by Bellam y and Gordon f o r P la ty p o e c ilu s m a c u la tu s ,
one o f t h e s p e c ie s i n t h i s gro u p .
2.
X iphophorus h e l l e r i i i s t h e o n ly member i n t h i s group b e s id e s
P la ty p o e c ilu s w hich has been s tu d ie d g e n e t i c a l l y , and, s in c e t h e ev id en ce
f o r s e x lin k a g e i n t h i s s p e c ie s i s n o t c l e a r , i t c a r r i e s l i t t l e w eight b e­
yond s u g g e s tin g th e p o s s i b i l i t y t h a t th e fem ale may be d ig a m e tic .
On th e
o th e r hand, t h e fre q u e n c y d i s t r i b u t i o n o f th e m easurem ents v/hen graphed
g iv e s a r a t h e r d e f i n i t e bim o d al c u rv e , w hich of c o u rse s u g g e s ts t h a t th e
se x chromosomes a r e n o t a l i k e .
T hus, from in s p e c tio n o f th e curve a lo n e ,
one m ight co n clu d e t h a t t h e D ro so p h ila ty p e o f sex mechanism o b ta in s .
t h e d i s t r i b u t i o n o f t h e t o t a l number o f m easurem ents sh o u ld be bim odal
when co m p ariso n s betw een r a t i o s o f p a i r s o f chromosomes g iv e d e f i n i t e l y
Why
n e g a tiv e t e s t s i s unknown.
P o s s ib ly t h e f a c t t h a t th e chromosomes o f X i-
phophorus w ere among t h e f i r s t t o have been measured, may account f o r some
o f th e v a r i a b i l i t y .
At l e a s t , i t i s q u it e c l e a r t h a t a n o th e r sam ple o r
two n eed s t o be t e s t e d .
However, s in c e t h e r e s u l t s o f c y to l o g ic a l o b se r­
v a t i o n and o f s t a t i s t i c a l and g e n e tic a n a ly s is a r e i n f a v o r o f a ZZ - ZW
ty p e o f i n h e r i t a n c e , f o r t h e tim e b e in g X iphophorus has been c o n d itio n a lly
in c lu d e d i n t h e ZZ - ZW g ro u p .
3«
The re m a in in g fo u r s p e c ie s , nam ely Gambusia panuco panuco,
M o ll i e n i s i a p e t e n e n s i s , M ic r o p o e c ilia b r a n n e r i and B rach y rh ap h is e p is c o p i,
have n o t b een w orked upon g e n e tic a lly *
S t a t i s t i c a l t e s t s betw een means
i n t h e s e f o u r s p e c ie s and betw een th e means o f X iphophorus h e l l e r i i and
P la ty p o e c ilu s m a cu la tu s w ere a l l n o n - s i g n i f i c a n t.
Thus a l l o f them may
be p la c e d i n t h e same g ro u p .
4*
The g e n e r a l c o n c lu s io n i s , th e n , t h a t b ecau se P la ty p o e c ilu s
and p o s s i b l y X iphophorus a r e g e n e t i c a l l y ZZ - ZW, and becau se th e s t a t i s ­
t i c a l d a ta seems t o f a v o r t h e i n t e r p r e t a t i o n t h a t th e sex chromosomes i n
a l l s i x s p e c ie s a r e o f s i m i l a r s i z e , i t seems p ro b a b le t h a t an Abraxas ty p e
o f s e x mechanism i s o p e r a tin g w ith in th e group r a t h e r th a n a m o d ifie d Droso­
p h i l a ty p e i n ?\rhich t h e X and Y chromosomes a r e m o rp h o lo g ic a lly a l i k e b u t
p h y s io l o g i c a l l y d i f f e r e n t .
A n o th er group o f f o u r s p e c ie s t e s t e d s i g n i f i c a n t l y w ith o n ly
one more a d d i t i o n a l s p e c ie s th a n d id th e s i x s p e c ie s i n t h e ZZ - ZW group.
tSpecies in c lu d e d i n t h i s group a r e :
Lim ia v i t t a t a , M o llie n is ia sphenops,
G la rv d ic h th y s f a l c a t u s and Gambusia a f f i n i s h o lb r o o k ii.
These may b elo n g
i n t h e ZZ - ZW group o r th e y may have sex chromosomes w hich a r e s l i g h t l y
d i f f e r e n t i n s i z e and p erh a p s b e lo n g t o t h e XX - XI group.
However, t h e
d i f f e r e n c e betw een t h i s group and t h e ZZ — ZW group a p p e a rs t o be so sm a ll
t h a t , u n t i l t h e ty p e o f se x mechanism i s e s ta b li s h e d g e n e t i c a l l y , i t may
be b e s t t o t e n t a t i v e l y p la c e them i n th e ZZ g ro u p .
An a d d i t i o n a l re a so n
f o r p l a c in g t h e two g ro u p s t o g e t h e r i s t h a t c l o s e ly r e l a t e d s p e c ie s o ccu r
i n them .
M o ll i e n i s i a sphenops and Gambusia panuco panuco o c c u r i n t h e ZZ
group w h ile M o ll i e n i s i a p e te n e n s is and Gambusia a f f i n i s h o lb ro o k ii o ccu r
i n t h e seco n d g ro u p .
S p e c ie s w ith compound h e te r o chromosome s .
Those s p e c ie s p o s s e s s in g compound se x chromosomes show a m o d ifi­
c a t i o n o f t h e D ro so p h ila XX — XY ty p e , i n w hich t h e X chromosome i s com­
pound.
A c l e a r cu t c a se f o r th e p re se n c e o f a compound Y chromosome has
n e v e r been d e s c rib e d i n a n im a ls , so t h a t th e c o n c lu s io n t h a t t h e compound
elem en ts r e p r e s e n t m u ltip le X chromosomes seems j u s t i f i e d .
The o r i g i n o f a compound X chromosome has been s a id t o be due
t o t h e fra g m e n ta tio n o f a s in g l e X chromosome.
However, t h i s th e o r y o f
o r i g i n does n o t ta k e i n t o c o n s id e r a tio n th e f a c t t h a t t h e X elem en ts a r e
c o n s ta n t th ro u g h o u t a s p e c ie s i n s i z e , number and form .
A ccording t o W il­
son (1 9 2 8 , p . 904) d i f f e r e n t p o r tio n s o f t h e X chromosome may become q u a l i ­
ta tiv e ly d iffe re n t.
Thus a s l i g h t in c r e a s e o f indep en d en ce on t h e p a r t o f
t h e q u a l i t a t i v e l y d i f f e r e n t components would cause them t o ap p e a r a s s e p a r a te
chromosomes.
I n su p p o rt o f t h e th e o r y i s th e o b s e rv a tio n t h a t i n many sp e­
c i e s w ith compound X elem en ts,, th e X elem en ts a s s o c ia te t o form one chromo­
some i n t h e g o n ia l d i v i s i o n s , and ap p e a r a s a complex o f d i s c r e t e b o d ie s
o n ly d u r in g t h e h e te r o ty p ic d i v i s i o n .
g in from a s in g l e chromosome.
Such b e h a v io r s u g g e s ts a common o r i ­
F u r th e r ev id en ce i n th e same d i r e c t i o n I s
a f f o r d e d by t h e p re s e n c e o f c o n s t r i c t i o n s o r s u tu r e s uoon th e chromosomes
o f many a n im a ls .
These a p p e a r c o n s ta n tly a t p a r t i c u l a r p la c e s upon th e
chromosomes and do n o t mark a p la n e o f d i v i s i o n .
Both se x chromosomes and
autosom es may be so m arked, and t h e s u tu r e s a r e p r e s e n t on b o th m i to t ic
and m e io tic chromosomes.
A cco rd ing t o W ilson (1928, p . 9 0 4 ), th e s u tu r e s
may mark ”t h e p o in t o f ju n c tu r e o f two c l o s e ly u n ite d components t h a t have
n o t, a s y e t , t h e v a lu e o f s e p a r a te chromosomes b u t m ight e a s i l y become
s u c h .”
I t i s p o s s i b l e t h a t t h e c o n s t r i c t i o n s o b serv ed upon t h e se x ch ro ­
mosomes o f some o f t h e P o e c i l i i d a e may be o f t h i s ty p e r a t h e r th a n c o n s tr i c ­
t i o n s i n d i c a t i n g t h e p la n e o f t h e e q u a tio n a l d i v i s i o n .
E vidence i n su p p o rt
o f t h i s s ta te m e n t i s :
1.
Some, b u t n o t a l l o f th e autosom es show s im ila r c o n s t r i c t i o n s .
2.
The s u tu r e s a p p e a r t o be I n t h e m edian t r a n s v e r s e p la n e and
t h e r e f o r e may n o t I n d ic a t e a f u tu r e p la n e o f d i v i s i o n .
However, i t i s d i f ­
f i c u l t t o d i s t i n g u i s h betw een th e t r a n s v e r s e and lo n g it u d i n a l ax es i n a
s h o r t r o d - l i k e chromosome.
U n f o rtu n a te ly , th e sm a lln e ss o f t h e seco n d ary
s p e rm a to c y te n u c l e i and t h e l a r g e number o f chromosomes p r e s e n t i n th e
g o n ia l n u c l e i make th e s tu d y o f in d i v i d u a l chromosomes m o rp h o lo g ic a lly
d iffic u lt.
T h e re fo re , one cannot conclude d e f i n i t e l y t h a t t h e median con­
s t r i c t i o n s a r e s t r u c t u r a l c h a r a c t e r i s t i c s o f th e chromosomes w ith no s ig ­
n if ic a n c e i n r e s p e c t t o t h e p la n e o f th e n ex t d i v is io n .
3.
An i n t e r e s t i n g o b s e rv a tio n , w hich may o r may n o t have a
b e a r in g upon t h e q u e s tio n o f t h e c h a r a c te r o f th e s e c o n s t r i c t i o n s , i s t h a t ,
w h ile none o f t h e se x chromosomes i n t h e s p e c ie s w ith compound sex chromo­
somes p o s s e s s e d m edian c o n s t r i c t i o n s , some o f th e autosom es had them .
Pos­
s i b l y , t h e n , t h e s e e le m e n ts r e p r e s e n t components o f a s in g le chromosome
w hich, t o u se W ilso n ’ s p h ra s e o lo g y , ” have a t t a i n e d th e v a lu e o f s e p a r a te
96:
chrom osom es. 11
Among1 a n im a ls w hich have compound, se x chromosomes th e s iz e r e l a ­
t i o n s h i p s b etw een t h e X com ponents and t h e Y a r e v a r i a b l e .
T here i s a ls o
c o n s id e r a b le v a r i a t i o n i n s i z e r e l a t i o n s h i p s among th o s e s p e c ie s o f Poe—
c i l i i d a e e x h i b i t i n g compound s e x chromosomes.
M a th e m a tic a l a n a l y s is o f th e m easurem ents o f s e x chromosomes and
c y t o l o g i c a l o b s e r v a tio n p e rm it
1*
t h e c o n c lu s io n s t h a t :
I n G ira rd in u s met a l i i cus a l l t h r e e sex chromosomes a r e o f
d iffe re n t s iz e s .
2.
same s i z e .
I n P la ty p o e c ilu s v a r i a t u s a l l t h r e e chromosomes a r e o f th e
I n t h i s s p e c ie s B ellam y, upon t h e b a s is o f r e s u l t s o b ta in e d
from i n t e r s p e c i f i c c r o s s e s , has concluded t h a t an XX - XY ty p e o f sex
mechanism o b t a i n s .
H is c o n c lu s io n i s now su p p o rte d by c y to lo g ic a l as
w e ll a s g e n e tic e v id e n c e .
3*
The s iz e r e l a t i o n s h i p s betw een t h e Y chromosomes and t h e X
chromosomes i n P o e c i l i o p s i s i n f a n s and M o llie n is ia l a t i p i n n a a r e s i m i l a r .
The Y chromosome i n b o th s p e c ie s i s l a r g e r th a n e i t h e r o f th e two X e le ­
m e n ts.
The X e le m e n ts ap p e a r t o be o f e q u a l s iz e i n P o e c il io p s is w h ile
i n M o l l i e n i s i a t h e y may d i f f e r s l i g h t l y .
4.
I n P o e c i l i s t e s p le u r o s p ilu s th e Y chromosome i s p ro b a b ly
s i m i l a r i n s iz e t o one o f t h e X chromosomes and th e t h r e e X chromosomes
d i f f e r i n s iz e from one a n o th e r .
C. Evidence f o r Vyd.tschi' s (1932) view point th a t
th e sex chromosomes in th e
P o e c illid a e are i n th e p ro cess o f e v o lu tio n :
1.
S tu d ie s made b o th i n th e f i e l d and i n th e la b o r a to r y have
shown t h a t s e x r a t i o s i n t h e P o e c i l i i d a e o f te n d i f f e r from t h e norm al 1 :1
sex r a t i o .
The p re v a le n c e o f a b e r r a n t r a t i o s i s s u g g e s tiv e o f i n s t a b i l i t y
i n t h e g e n e tic s e x d e te rm in in g m echanism .
I f W itsc h i* s assu m p tio n i s v a l i d
one w ould e x p e c t t o f in d some d e v ia tio n from t h e norm al sex r a t i o .
2.
A number o f i n v e s t i g a t o r s have r e p o r te d c a se s o f se x r e v e r s a l
and have a t t r i b u t e d th e abnorm al s e x r a t i o t o t h i s phenomenon.
However, i t
i s p ro b a b le t h a t se x r e v e r s a l i s n o t as common a s i t has been assumed t o be
T h e re i s e v id e n c e t h a t s e x u a l m a tu r ity may be p o stp o n ed f o r a lo n g p e rio d
o f tim e , d u r in g w hich tim e t h e f i s h in c r e a s e i n s iz e u n t i l th e y a r e ab­
n o rm a lly l a r g e .
An i n d i v i d u a l o f t h i s ty p e , ex cep t f o r s i z e , i s pheno-
t y p i c a l l y l i k e a n o r d in a ry fe m a le .
However, G. L. T u rn er and E d ith B.
Hansen have shown t h a t t h e gonads i n th e s e f i s h a r e n o t m a tu re .
When sex­
u a l m a t u r i t y i s a t t a i n e d , i f f i s h o f t h i s ty p e become m ale, i t i s o f te n
r e p o r te d a s a f i s h w hich has undergone se x r e v e r s a l .
B ou len g er, E ssen b erg ,
and Gordon and Hubbs have made su ch i n t e r p r e t a t i o n s .
I t seems th e n t h a t
s e x u a l m a tu r ity may som etim es be d e la y e d a s i t i s i n th e u n d i f f e r e n t i a t e d
r a c e s o f f r o g s , and t h a t s e x r e v e r s a l i s n o t a common o c c u rre n c e .
Such a
c o n c lu s io n le n d s s u p p o rt t o W its c h i’ s th e o r y .
3.
On t h e o th e r hand, Winge’ s r e s e a r c h showrs t h a t u n d e r con­
t r o l l e d l a b o r a t o r y e x p e rim e n ta tio n , i n s to c k s w hich have r e s u l t e d from
c lo s e in b r e e d in g th ro u g h many g e n e r a tio n s , th e s e x d e te rm in in g mechanism
may be a l t e r e d .
By c o n t r o ll e d b re e d in g he was a b le t o change th e XX - XY
ty p e o f se x m echanism o p e r a tin g i n L e b is te s t o th e A braxas ZZ - ZW ty p e
o p e r a tin g i n P l a t y p o e c i l u s .
T hus, i f th e s e r e s u l t s a re r e l i a b l e , th e sex
d e te rm in in g mechanism o p e r a tiv e i n t h i s to p minnow i s u n s ta b le .
In s ta ­
b i l i t y o f t h e s e x d e te rm in in g mechanism m ight be e x p ected i n a group i n
w h ich g e n e tic c o n t r o l o f se x i s i n th e p ro c e s s o f e v o lu tio n .
4*
The f a c t t h a t c r o s s in g o v er o ccu rs betw een g e n e tic f a c t o r s
i n t h e X and Y chromosomes o r betw een th o s e i n t h e W and Z chromosomes
p o i n t s t o t h e c o n c lu s io n t h a t t h e s e x chromosomes a r e n o t y e t w e ll d i f f e r ­
e n t i a t e d and e x h i b i t b e h a v io r w hich i s more c h a r a c t e r i s t i c o f autosom es
th a n o f w e ll d e f in e d s e x chromosomes.
5*
The ab sen ce o f an extrem e ty p e o f h e te ro p y c n o s is d u rin g th e
grow th s ta g e s o f t h e a u x o c y te s a ls o i n d i c a t e s t h a t th e sex chromosomes i n
th e P o e c i l i i d a e have n o t become d i f f e r e n t i a t e d t o such an e x te n t t h a t th e y
have l o s t a l l o f t h e b e h a v io r c h a r a c t e r i s t i c o f autosom es.
6.
E v id en ce f o r t h e o c c u rre n c e o f b o th th e A braxas and Droso­
p h i l a ty p e o f se x d e te r m in a tio n w ith in a s in g le fa m ily may a ls o le n d sup­
p o r t t o W i t s c h i 's t h e o r y .
A su rv e y o f t h e c y to g e n e tic l i t e r a t u r e ,
o f t h e s e x chromosomes i n a number o f P o e c ili id a e
and c y to lo g i c a l stu d y
a f f o r d ev id en ce f o r t h e
e x is te n c e o f a
s e x mechanism w hich i s n o t a s s t a b l e a s t h a t
i n many o th e r
fo rm s.
i t a p p e a rs t h a t t h e r e i s a c o n s id e ra b le body
o f e v id en ce i n
Hence,
f a v o r o f W i t s c h i 's t h e o r y t h a t t h e se x chromosomes i n th e P o e c i liid a e a r e
i n t h e p ro c e s s o f e v o lv in g .
D.
S in c e t h e r e i s ev id en ce f o r c y t o l o g i c a l l y o b s e rv a b le sex chromosomes
in th e P o e c iliid a e , th o s e th e o r ie s of sex
upon a b a la n c e
d e te rm in a tio n w hich a r e b ased
betw een sex d e te rm in e rs i n th e autosom es and
i n th e se x
chromosomes seem more te n a b le th a n t h e th e o r y o f Kosswig and Bredder which
i s b a s e d upon t h e ab sen ce o f se x chromosomes.
E.
Summary and C o n c lu sio n s
1.
s tu d i e d .
H etero chromosomes a r e found i n a l l s p e c ie s o f P o e c ili id a e
F i f t e e n s p e c ie s p o s s e s s two heterochrom osom es, f iv e s p e c ie s have
t h r e e , and one s p e c ie s f o u r .
2.
The b e h a v io r o f t h e heterochrom osom es i s so s im i l a r t o t h a t
o f t h e s e x chromosomes i n o th e r an im als t h a t t h e c o n c lu s io n i s drawn t h a t
t h e heterochrom osom es i n t h e P o e c ili id a e form a p a r t o f th e sex d e te rm in in g
mechanism i n t h e g ro u p .
3*
The two s e x chromosomes i n f i v e s p e c ie s a r e n o t o f th e same
s iz e and a r e i n t e r p r e t e d a s X and Y chromosomes.
F or two o f th e s e f iv e
s p e c ie s t h e r e i s a ls o g e n e tic e v id en ce i n su p p o rt o f t h i s c o n c lu s io n .
4.
T h ere i s e v id e n ce t h a t t e n o f th e tw e n ty s p e c ie s p o s se s s an
A braxas ty p e o f s e x m echanism .
G en etic ev id en ce i n r e g a rd t o two o f t h i s
group i s i n a c c o rd w ith t h e c o n c lu s io n .
5.
S p e c ie s w ith compound se x chromosomes a r e c o n s id e re d t o have
an XX - XY ty p e o f s e x d e te rm in a tio n i n w hich th e X elem en ts a r e m u lt ip l e .
F our o f t h e s e f iv e s p e c ie s have two X components and one o f them shows
th re e .
6.
A th e o r y o f se x d e te r m in a tio n , su ch as t h a t o f B re id e r and
Kossw ig w hich assum es t h e ab sen ce o f se x chromosomes, i s n o t a s much i n
l i n e w ith t h e r e s u l t s o f g e n e tic and c y to lo g ic a l s tu d ie s i n th e s e f is h e s
a s t h e t h e o r i e s b ased upon a b a la n c e betw een male and fem ale d e te rm in e rs
lo c a t e d b o th i n t h e autosom es and i n a p a i r o f se x chromosomes.
7.
As a r e s u l t o f a su rv e y o f c y to g e n e tic l i t e r a t u r e , and upon
th e b a s i s o f c y t o l o g i c a l o b s e r v a tio n , i t i s concluded t h a t t h e r e i s e v i­
dence i n su p p o rt o f W i t s c h i 's th e o r y t h a t th e sex chromosomes i n th e P oe-
.
100
c i l i i d a e a r e i n t h e p ro c e s s o f e v o lv in g from autosom es.
ACKNOWLEDGMENTS
I v/ish t o e x p re s s my a p p r e c ia tio n t o P r o f e s s o r C. L. T u rn e r f o r
a l l o f h is h e lp and a d v ic e on t h i s s tu d y .
I am g r a t e f u l a l s o t o P r o f e s s o r Frank A. Brown, J r . f o r s u g g e s tin g
a m ethod f o r s tu d y in g chromosome s iz e and f o r v a lu a b le c r i t i c i s m o f th e
re s u lts .
I t i s w ith e q u a l p le a s u r e t h a t I acknow ledge th e a s s i s ta n c e o f
P r o f e s s o r Eugen A lts c h u l I n a c q u ir in g t h e fu n d am en tals o f s t a t i s t i c a l
m ethodology and t h e a s s i s t a n c e o f P r o f e s s o r Sevra.ll W right i n w orking out
a s t a t i s t i c a l m ethod a p p lic a b le t o t h i s problem .
I w ish t o th a n k P r o f e s s o r A. E. T r e lo a r and P r o f e s s o r R. A.
F is h e r f o r l e t t e r s w hich c o n ta in e d h e lp f u l s u g g e s tio n s , and P r o f e s s o r C.
L. Hubbs f o r t h e lo a n o f r e p r i n t s u n o b ta in a b le e lse w h e re .
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E . 1899
o f in s e c ts .
A p e c u l i a r n u c le a r elem ent i n m ale r e p ro d u c tiv e c e l l s
Z o o l. B u l l . , 2 ( 4 ) : 187- 197.
i --------------------1900
The sp e rm a to c y te d iv is io n s o f t h e a c r i d i d a e .
U n i. Q u a r t., S e r . A, 9 ( l ) : 73-100.
1902
: --------------------3 ( 4 ) :4 3 - 8 4 .
The a c c e s s o ry chromosome— se x d e te rm in a te
Kan.
B io l. B u l l . ,
---------------------------- 1918 P o s s ib le a c tio n o f t h e s e x -d e te rm in in g mechanism.
P ro c . N a t. Acad. S c i . , 4 ( 6 ) : l 6 0 - l 6 3 .
P r o k o fie v a , A.
1934 On t h e chromosome m orphology o f c e r t a i n P is c e s .
C y to lo g ia , 5 ( 4 ) 1498- 506.
R a ls to n , E. M.
1934 A s tu d y o f th e chromosomes o f X iphophorus, P la ty p o e ­
c i l u s and X ip h o p h o ru s -P la ty p o e c ilu s h y b rid s d u rin g s p e rm a to g e n e s is.
J . M orph., 56 ( 3 ) : 423- 443.
Reed, H. D. and M. Gordon
1931
The m orphology o f m e la n o tic overg ro w th s .
i n h y b rid s o f M exican k i l l i f i s h e s .
Am. J . C ancer, 15 (3):1524-1537*
Reed, H. D ., M. Gordon and W. L an sin g
1933 S tudy o f t h e p o st-em b ry o n ic
grow th o f an h e r e d i t a r y m e la n o tic neoplasm i n h y b rid s betw een two
f i s h s p e c ie s .
A n at. R e c ., 57 ( 4 ) : 107 S u p p l., A b st. No. 181.
Sim pson, G. and A. Roe
V au p el, J .
Q u a n tita tiv e Zoology.
M cG raw -H ill, New Y ork.
1929
The sp e rm a to g e n e sis o f L e b is t e s . r e t i c u l a t u s .
and P h y s i o l ., 47 (2 ):5 5 5-573*
Y filson, E . B.
W inge, 0 .
1939
1928
The C e ll i n Development and H e re d ity .
J . Morph,
M acm illan.
1922a
A p e c u l i a r mode o f in h e r ita n c e and i t s c y to l o g ic a l ex­
p la n a tio n .
J . G e n e tic s , 12:137-144*
--------------------1922b
O n e-sid ed m a sc u lin e and s e x - lin k e d in h e r it a n c e i n
L e b is te s r e t i c u l a t u s .
J . G e n e tic s , 12:145—162.
_____________
1923 C ro s s in g -o v e r betw een th e X and Y chromosome i n
L e b is t e s .
J . G e n e tic s , 13 (2):2 0 1 -2 1 7 *
______________
1927 The l o c a t i o n o f e ig h te e n genes i n L e b is te s r e t i c u l a t u s .
J . G e n e tic s , 18 ( l ) : l - 4 3 *
____________
1930
On th e o c c u rre n c e o f XX m ales i n L e b is te s r e t i c u l a t u s .
w ith some rem arks on A id a 's s o - c a l l e d 11n o n - d is ju n c tio n a l" m ales i n
A p lo c h e ilu s .
J . G e n e tic s , 23 ( l) : 6 9 - 7 6 .
______________
1934a
The e x p e rim e n ta l a l t e r a t i o n o f se x chromosomes i n t o
autosom es and v i s a v e r s a , a s i l l u s t r a t e d by L e b is t e s .
C. R. Lab.
C a rls b e rg S e r . P h y s ., 21 ( l ) : l - 5 0 .
W inge, 0
1934b
The n a tu r e o f s e x chromosomes.
Pro.c. S ix th I n t e r n a t .
Cong. G e n e tic s , I t h a c a , N. Y ., 1 :3 4 3 -3 5 5 -
W its c h i, E. 1932
Sex d e v i a t i o n s , in v e r s io n s and p a r a b i o s i s . Sex and
I n t e r n a l S e c r e t i o n s , Chap. 5> 160-234B a ltim o re . W illiam s
and W ilk in s .
GENERAL EXPLANATION OF FIGURES
A ll f i g u r e s a r e cam era l u c id a drav<dngs drawn t o t h e same s c a l e .
M a g n if ic a tio n :
2320.
S paces have been l e f t f o r f ig u r e s f o r P h allich fch y s am ates and Gambusia
a f f i n i s , two s p e c ie s w hich w ere re c e iv e d to o l a t e t o be in c lu d e d a t
t h e p r e s e n t tim e .
F ig u re s 1 -7 1 :
a.
T hese a r e a l l l a t e r a l view s o f t h e m etaphase s ta g e o f th e p rim ary
s p e rm a to c y te d i v i s i o n .
b.
The s p in d l e s , w hich a r e of th e a n a s t r a l ty p e , a r e shown by means
o f d o tte d l i n e s .
c.
The c e n t r i o l e s a r e shown a s d o ts a t t h e p o la r ends o f t h e s p in d le s .
d*
The autosom es a re shown m assed upon t h e e q u a t o r i a l p l a t e s .
e.
The s e x chromosomes a r e i s o l a t e d from th e autosom es upon th e equa­
t o r i a l p l a t e s but a r e a tta c h e d t o th e s p in d le s by f i b e r s .
When
su ch f i b e r s co u ld be o b serv ed th e y a r e in d ic a te d by d o tte d l i n e s .
F ig u re s 72-100:
a.
T hese a r e a l l p o la r view s o f th e m etaphase o f t h e p rim a ry sperm a­
to c y te d iv is io n .
b.
The autosom es have sp re a d out upon t h e p l a t e but have n o t y e t
d iv id e d .
c.
The s e x chromosomes a re i n th e anaphase s ta g e and w h ile i s o l a t e d
from th e group o f autosom es, a r e a tta c h e d t o th e c e n t r a l group
by s p in d le f i b e r s .
B eh a v io r o f t h e se x chromosomes i s s im ila r enough t o p erm it an a r b i ­
t r a r y d i v i s i o n o f t h e i r b e h a v io r i n t o t h r e e s ta g e s :
S ta g e a .
At t h i s tim e t h e se x chromosomes a r e a s s o c ia te d , and may
be o b se rv e d as la r g e la g g in g b o d ie s i s o l a t e d a t t h e p e r i ­
p h e ry o f t h e s p in d le .
They a r e , how ever, a tta c h e d t o t h e
s p in d le by a f i b e r .
S ta g e b .
A s ta g e o f p re c o c io u s m etaphase f o r t h e se x chromosomes,
a t w h ich tim e th e y undergo r e d u c tio n a l d i v i s io n .
They ap­
p e a r a s s e p a r a te chromosomes, w hich w h ile a tta c h e d t o th e
s p i n d l e , a r e i s o l a t e d a t i t s p e r ip h e r y .
S ta g e £ .
A s ta g e o f p re c o c io u s anaphase f o r th e sex chromosomes.
They may be o b serv ed p a s s in g t o t h e p o le s , p re c e d in g th e
autosom es w hich have not y e t d iv id e d .
PLATE I
Explanation of Figures
1.
P seudoxiphophorus b im a c u la tu s S tag e a .
2.
L e b is te s r e t i c u l a t u s S tag e a .
3.
L inda n i g r o f a s c i a t a S tag e a .
4.
H e te ra n d ria form osa S tag e a .
5.
Q uin tan a a tr iz o n a S tag e a .
6•
Lim ia v i t t a t a S tag e a .
7.
M o llie n is ia sphenops S tag e a .
8.
G la ry d ic h th y s f a l c a t u s S tag e a .
9.
Gambusia a f f i n i s h o lb ro o k ii S tag e a .
10.
M ic ro p o e c ilia b r a n n e ri S tag e a .
11.
X iphophorus h e l l e r i i S tag e a .
12.
Gambusia panuco panuco S tag e a .
13.
M o llie n is ia p e te n e n s is S tag e a .
14.
B rach y rh ap h is e p is c o p i S tag e a .
Note t e t r a d - l i k e ap p earan ce
due t o median c o n s tr i c t i o n s i n each o f th e sex chromosomes.
15*
P la ty p o e c ilu s m acu latu s S tage a .
Note t e t r a d - l i k e ap p earan ce
o f la g g in g body due t o m edian c o n s tr i c t i o n s i n each o f th e s e x ch ro ­
mosomes.
17- G ira rd in u s met a l i i cus S tag e a .
I n t h i s s p e c ie s th e la r g e
la g g in g body i s o l a t e d on th e p e rip h e ry o f th e s p in d le i s d e f i n i t e l y
trip a rtite .
18.
P o e c i l i s t e s p le u r o s p ilu s S tag e a .
The l a r g e la g g in g body
i s o l a t e d on t h e p e r ip h e ry o f th e s p in d le i s q u a d r i p a r t i t e .
19.
P o e c i l i o p s i s in f a n s S tag e a .
20.
M o llie n is ia l a t i p i n n a S tag e a .
Lagging body t r i p a r t i t e .
Lagging body t r i p a r t i t e .
PLATE II
Explanation of Figures
21.
G ira rd in u s met a l i i cus S tag e b .
At th e end o f th e r e d u c tio n a l
d i v is io n t h e r e a r e t h r e e sex chromosomes i s o l a t e d on t h e p e r ip h e ry o f
t h e s p in d le .
22.
G ira rd in u s met a l i i cus S tage b .
E a rly s ta g e i n t h e r e d u c tio n a l
d i v i s i o n showing d i v is io n o f th e t r i p a r t i t e body i n t o a p a i r o f a s so ­
c ia te d chromosomes and a s in g le chromosome.
24.
P la ty p o e c ilu s m aculatus S tage b .
Note m edian c o n s tr i c t i o n i n
one o f th e sex chromosomes.
25.
B racb y rh ap h is e p is c o p i S tage b .
Note m edian c o n s tr i c t i o n s
i n b o th o f sex chromosomes.
26.
M o llie n is ia p e te n e n s is S ta g e b.
27.
Gambusia panuco panuco S tage b .
28.
Xiphophorus h e l l e r i i S tage b .
Note m edian c o n s t r i c t i o n s i n
b o th se x chromosomes*
29*
M ic ro p o e c ilia b r a n n e ri S tage b .
30.
Gambusia a f f i n i s h o lb ro o k ii S tage b .
31.
G la ry d ic h th y s f a l c a t u s S tage b .
32.
M o llie n is ia sphenops S tage b .
33»
Lim ia v i t t a t a S tag e b .
34•
Q uintana a t r iz o n a S tag e b .
Note m edian c o n s tr i c t i o n s upon
t h e se x chromosomes.
33*
H e te ra n d ria forniosa S tag e b.
t h e sex chromosomes.
36.
Lim ia n i g r o f a s c i a t a S tag e b.
Note m edian c o n s tr i c t i o n s upon
PLATE I I (C ontinued)
37*
L e b is te s r e t i c u l a t u s S tag e b .
Note m edian c o n s tr i c t i o n s upon
t h e sex chromosomes.
3&.
P s eudoxip hop ho r us b im acu latu s S tage b .
40.
P la ty p o e c ilu s v a r i a t u s S tag e a .
Lagging body t r i p a r t i t e .
PLATE I I I
E x p la n a tio n o f F ig u re s
4.1*
P o e c i l i s t e s p le u r o s p ilu s S tag e b .
m etap h ase.
42.
Sex chromosomes i n e a r l y
Note s in g le chromosome and la r g e t r i p a r t i t e body.
P o e c i l i s t e s p le u r o s p ilu s S tag e b .
m etap h ase.
Sex chromosomes i n l a t e
Note t h a t t h e t r i p a r t i t e body o f F ig . 41 seems t o have
d iv id e d .
43. P o e c ilio p s is in f a n s
p h a se.
43*
M o llie n is ia l a t i p i n n a S tage b.
46.
chromosomes i n l a t e m eta­
Sex chromosomes i n e a r l y
Note s in g le chromosome and l a r g e r double body.
M o llie n is ia l a t i p i n n a S tage b . Sex chromosomes i n
m etap h ase.
Double body o f F ig . 45 seems t o
P la ty p o e c ilu s v a r i a t u s S tag e b .
m etap h ase.
48 .
S tag e b . Sex
Double body o f F ig . 43 seems t o have d iv id e d .
m etap h ase.
47-
chromosomes i n e a r l y m eta­
Note s in g le chromosome and l a r g e r double body.
44- P o e c i l i o p s i s in f a n s
p h a se .
S tage b . Sex
have d iv id e d .
Sex chromosomes i n e a r ly
Note s in g le chromosome and l a r g e r double body.
P la ty p o e c ilu s v a r i a t u s S tag e b .
m etap h ase.
la te
Sex chromosomes i n l a t e
Double body o f F ig . 47 seems t o have d iv id e d .
51.
P seudoxiphophorus b im acu latu s S tag e c.
52.
L e b is te s r e t i c u l a t u s S tag e c .
Note c o n s tr i c t i o n s i n
se x
chromosomes.
53*
Lim ia n i g r o f a s c i a t a
S tage c .
54*
H e te ra n d ria form osa
S tage c .
Note c o n s tr i c t i o n s
i n sex
chromosomes.
55*
mosomes.
Q u in tan a a t r iz o n a S tag e c .
Note c o n s tr i c t i o n s i n sex ch ro ­
PLATE I I I (C ontinued)
56.
Lim ia v i t t a t a S tage c.
57*
M o llie n is ia sphenops S tag e c .
58.
G la ry d ic h th y s f a l c a t u s S tag e c .
59*
Gambusia a f f i n i s h o lb ro o k ii S tag e c .
60 .
M ic ro p o e c ilia b ra n n e ri S tage c .
PLATE IV
Explanation o f Figures
61.
X iphophorus h e l l e r i i S tag e c .
Note m edian c o n s tr i c t i o n s i n
s e x chromosomes.
62.
Gambusia panuco panuco
S ta g e c .
63.
M o llie n is ia p e te n e n s is
S tag e c .
B rach y rh ap h is e p is c o p i S tag e c .
Note median, c o n s tr i c t i o n s i
se x chromosomes.
65-
P la ty p o e c ilu s m acu latu s S ta g e c .
Note m edian c o n s tr i c t i o n s
i n sex chromosomes.
67*
G ira rd in u s met a l i i cus S ta g e c .
T hree se x chromosomes.
68.
P o e c i l i s t e s p le u r o s p ilu s S ta g e c .
69.
P o e c i l i o p s i s in f a n s S tag e c .
70.
M o llie n is ia l a t i p i n n a S tag e c .
71<
P la ty p o e c ilu s v a r i a t u s
73*
P seudoxiphophom s b im a c u la tu s . _ P o la r view o f m etaphase
Four s e x chromosomes.
T hree s e x chromosomes.
T hree se x chromosomes.
S ta g e c . T hree
sex chromosomes.
s ta g e show ing sex chromosomes i n t h e anaphase s ta g e .
Note m edian
c o n s t r i c t i o n s on some o f autosom es.
74*
L e b is te s r e t i c u l a t u s .
Same s ta g e a s d e s c rib e d f o r F ig . 73-
Note c o n s t r i c t i o n on th e s e x chromosome.
75*
Lim ia n i g r o f a s c i a t a .
Same s ta g e a s d e s c rib e d f o r F ig . 73*
Note c o n s t r i c t i o n on some o f t h e autosom es.
76.
H e te ra n d ria fo rm o sa.
Same s ta g e a s d e s c rib e d f o r F ig . 73 .
Note c o n s t r i c t i o n s on some o f th e autosom es and se x chromosome.
77*
Q u in tan a a t r i z o n a .
Note c o n s t r i c t i o n s .
Same s ta g e a s d e s c rib e d f o r F ig . 73.
PLATE IV (C ontinued)
7B.
Linda v i t t a t a .
Same s ta g e as f o r F ig .
73*
Note autosom al
c o n s tric tio n s .
79.
M o llie n is ia sph en ops.
80.
G la ry d ic h th y s f a l c a t u s .
Same s ta g e a s d e s c rib e d i n F ig . 73*
Same s ta g e as d e s c rib e d i n F ig . 73*
PLATE V
Explanation o f Figures
81.
Gambusia a f f i n i s h o lb r o o k ii.
P o la r view o f m etaphase s ta g e
showing se x chromosomes i n anaphase s ta g e .
82.
M ic ro p o e c ilia b r a n n e r i.
Same s ta g e a s t h a t d e s c rib e d f o r
F ig . 81.
83.
X iphophorus h e l l e r i i .
Same s ta g e a s t h a t d e s c rib e d f o r
F ig . 81.
84.
Gambusia panuco panuco.
Same s ta g e a s t h a t d e s c rib e d f o r
M o llie n is ia p e te n e n s is .
Same s ta g e a s t h a t d e s c rib e d f o r
Brac hyrhap h i s e p is c o p i.
Same s ta g e as t h a t d e s c rib e d f o r
F ig . 81.
85.
F ig . 81.
86.
F ig . 81.
87*
P la ty p o e c ilu s m a c u la tu s .
Same s ta g e as t h a t d e s c rib e d f o r
F ig . 81.
89.
F ig . 81.
G ira rd in u s m e t a l i i c u s .
Same s ta g e a s t h a t d e s c rib e d f o r
One o f t h e t h r e e sex chromosomes shown.
Note t h e m edian
c o n s t r i c t i o n s upon t h e autosom es b u t n o t upon th e se x chromosome.
90.
F ig . 81.
G ira rd in u s met a l i i c u s .
Same s ta g e a s t h a t d e s c rib e d f o r
Two o f t h e t h r e e s e x chromosomes shown.
N ote m edian con­
s t r i c t i o n s upon t h e autosom es b u t not upon t h e se x chromosomes.
91.
F ig . 81.
92.
F ig . 81.
P o e c ilis te s p le u ro s p ilu s .
Same s ta g e a s t h a t d e s c rib e d f o r
One o f t h e f o u r se x chromosomes shown.
P o e c ilis te s p le u ro s p ilu s .
Same s ta g e a s t h a t d e s c rib e d f o r
T h ree o f t h e f o u r sex chromosomes shown.
PLATE V (C ontinued)
9381.
Same s ta g e a s t h a t d e s c rib e d f o r F ig
One o f t h e t h r e e s e x chromosomes shown.
94*
81.
P o e c ilio p s is in f a n s .
P o e c ilio p s is in f a n s .
Same s ta g e as t h a t d e s c rib e d f o r F ig
Two o f t h e t h r e e s e x chromosomes shown.
95-
F ig . 81.
96.
F ig . 81.
97F ig . 81.
96F ig . 81.
M o llie n is ia l a t i p i n n a .
Same s ta g e a s t h a t d e s c rib e d f o r
One o f t h e t h r e e sex chromosomes shown.
M o llie n is ia l a t i p i n n a .
Same s ta g e a s t h a t d e s c rib e d f o r
Two o f th e t h r e e s e x chromosomes shown.
P la ty p o e c ilu s v a r i a t u s .
Same s ta g e a s t h a t d e s c rib e d f o r
One o f t h e t h r e e se x chromosomes shown.
P la ty p o e c ilu s v a r i a t u s .
Same s ta g e a s t h a t d e s c rib e d f o r
Two o f th e t h r e e sex chromosomes shown.
Plate
V
GRAPH 1
Pseudoxiphophorus b im acu latu s Heck e l
Frequency C la sse s
o f M easurem ents
(A b sc issa )
2 .6 8 - 2 .7 7 mm.
2 .7 8 - 2 .8 7
2 .8 8 - 2 .9 7
2 .9 8 - 3 .0 7
3 .0 8 - 3 .1 7
3 .1 8 - 3 .2 7
3 . 2.8 - 3 .3 7
3 .3 8 - 3 .1 7
3 .1 8 - 3 .5 7
3 .5 S - 3 .6 7
3 .6 8 - 3*77
3 .7 8 - 3 .8 7
3 .8 8 and o v er
D is tr i b u tio n
( Ordi]
1
7
8
21
20
13
7
6
7
0
2
3
2
GRAPH 2
L e b is te s r e t i c u l a t u s P e te r s
F requency C la sse s
o f M easurem ents
(A b sc issa )
2 .1 1 - 2 .2 3 mm.
2 .2 1 - 2 .3 3
2 .3 1 - 2 .1 3
2 . U - 2 .5 3
2 .5 1 - 2 .6 3
2 .6 1 - 2 .7 3
2 .7 1 - 2 .8 3
2 .8 1 - 2 .9 3
2 .9 1 - 3 .0 3
3 .0 1 - 3 .1 3
3 .1 1 - 3 .2 3
3 .2 1 - 3 .3 3
3 .3 1 - 3 .1 3
3 .1 1 - 3 .5 3
3 .5 1 - 3-63
3 .6 1 - 3 .7 3
3 .7 1 - 3 .3 3
3 .8 1 - 3 .9 3
3-91 - U.03
l . o i - U-13
1*11 — U.2 3
1.2-4 - A-33
1 .3 1 - 1 .1 3
1 .1 1 - 1 .5 3
1 .5 1 - 1 .6 3
1 .6 1 - 1 .7 3
1 .7 1 and o v er
Di s t r ib u t io n
(O rdir
1
1
1
1
1
1
1
10
9
2
1
5
2
8
9
1
5
1
1
2
3
3
0
1
3
1
2
21
Graph I
Pseudoxiphophorus bimaculatus Heckel
13
II
S
5
3
2.68 2.88 3 .0 8 3.28 3.48 3.68 3.88 4-08
Z
reticu /a tu s Peters
G ra p h
i9 e
Leb/'stes
First
~l
11
1 11
I
I I I
I I
Sample
J _ 1 - L J __L _ i _ L I
L L
2J4 2.24 2.5;T 2.74 2.94 3)4 ’3.34 3.54 3.74 3.94 4.14 4.34 4.54 4.74 4.94
GRAPH 3
L e b is te s r e t i e u l a t u s P e te r s
(A b sc issa )
Frequency C la s se s
o f M easurements
2 .5 8 - 2 .6 7 nim.
2. 6 8 - 2 . 7 7
2 .7 8 - 2 .8 7
2.88
2 .9 7
2 .9 8 - 3 .0 7
3 .0 8 - 3 .1 7
3 .1 8 - 3 .2 7
3 .2 8 - 3 .3 7
3 .3 8 - 3 .4 7
3 .4 8 - 3 -5 7
3 .5 8 - 3 .6 7
3 .6 8 - 3 .7 7
3 .7 8 - 3-87
3.88
3-97
3 .9 8 - 4 .0 7
4 .0 8 - 4 .1 7
4 .1 8 - 4 .2 7
-
-
D i s tr ib u t io n
(O rd in a te )
3
2
6’
9
11
9
10
5
6
7
8
3
7
8
’ 2
2
2
GRAPH 4
L e b is te s r e t i c u l a t u s P e te r s
(A b sc issa )
F requency C la sse s
o f M easurem ents
2 .1 4 - 2 .2 3 nim.
2 .2 4 - 2 .3 3
2 .3 4 - 2 .4 3
2 .^ 4 - 2 .5 3
2 .5 4 - 2 .6 3
2 .6 4 -* 2 .7 3
2 .7 4 - 2 .8 3
2 .8 4 - 2 .9 3
2 .9 4 - 3 .0 3
3 .0 4 - 3 .1 3
3 .1 4 - 3 .2 3
3 .2 4 - 3 .3 3
3 .3 4 - 3 .4 3
3 .4 4 - 3 .5 3
3 .5 4 - 3 .6 3
3 .6 4 - 3-73
3 .7 4 - 3 .8 3
3 .8 4 - 3-93
3 .9 4 - 4 .0 3
4 .0 4 - 4 .1 3
4 .1 4 - 4 .2 3
4 .2 4 - 4-33
4 .3 4 - 4*43
4*44 — 4*53
4 .5 4 - 4-63
4 .6 4 — 4*73
4 .74 and o v e r
D i s tr i b u tio n
(O rd in a te )
1
1'
1
4
6
5
10
16
20
9
15
12
12
13
16
9
10
11
9
5
5
3
0
1
3
1
2
23
21
19
17
Graph
L e b iste s
3
r e t i c u i a t u s Pe ters
Second
S a m p le
15
13
II
9
7
5
3
I
2.58 2.78 2.98 3.18 3 3 8 3.58 3.78 3.98 4.18
23
21
19
G r a ph
4-
L e b is te s re tie u la tu s
Combination
of
Peters
£ a nd 3
17
15
13
II
9
7
5
3
I
2.14 2.34 2.54 274 2.94 3.14 3.34 3.54 3.74 3.94 4.14 4.34 4.54 4.74
GRAPH 5
Lim ia n ig r o f a s c i a t a Hegan
Frequency C la s se s
o f M easurements
(A b sc issa )
2 .3 8 - 2 .4 7 mm.
2 .4 8 - 2 .5 7
2 .5 8 - 2 .6 7
2.68 - 2.77
2 .7 8 - 2 .8 7
2 .8 8 - 2 .9 7
2 .9 8 - 3 .0 7
3 .0 8 - 3 .1 7
3 .1 8 - 3 .2 7
3 .2 8 - 3-37
3-38 - 3 .4 7
3 .4 8 - 3 .5 7
3-58 - 3 .6 7
3 .6 8 - 3 .7 7
3 .7 8 - 3 .8 7
D is tr i b u t i o n
(O rd in a te )
1
0
3
2
8
10
16
11
11
16
10
8
1
1
2
GRAPH 6
M o llie n is ia sphenops C u v ier and V alen cien n es
Frequency C la s se s
o f M easurem ents
(A b sc issa )
2 .6 7 - 2 .76 mm.
2 .7 7 - 2.86
2 .8 7 - 2.9 6
2 .9 7 - 3.06
3 .0 7 - 3.16
3 .1 7 - 3.26
3 .2 7 - 3.36
3 .3 7 - 3.46
3 .4 7 - 3.56
3 .5 7 - 3.66
3 .6 7 - 3.76
3 .7 7 - 3.86
3 .8 7 - 3.96
3 .9 7 and o v er
D is tr i b u t i o n
(O rdir
2
0
2
4
6
16
24
13
11
8
6
1
5
2
Graph
5
Lim ia n ig r o fa s c /a ta
Re oa n
23 8 2.58 2.78 2.98 3.18 3.38 3.58 3.78
Graph
6
Lioffie n is ia sph enops
and
2.67 2.87 3.07 3.27 3.47 3.67 3.87, 4.07
Cuvier
Valenciennes
GRAPH 7
Gambusia panuco panuco Hubbs
F req u en cy C la sse s
o f M easurem ents
(A b sc issa )
2 .4 5 - 2 .5 4
2 .5 5 - 2 .6 4
2 .6 5 - 2 .7 4
2 .7 5 - 2 .8 4
2 .8 5 - 2 .9 4
2.9 5 - 3 .0 4
3.0 5 - 3 .1 4
3 .1 5 - 3 .2 4
3.25 - 3 .3 4
3 .3 5 - 3 .4 4
3.4 5 - 3 .5 4
3 .5 5 - 3 .6 4
3.65 - 3 .7 4
3.7 5 - 3 .8 4
3.85 and o v er
D is tr i b u t i o n
(Ordi:
22
3
1
4
5
15
20
13
17
5
6
6
1
1
1
GRAPH 8
M ic ro p o e c ilia b r a n n e ri Eigenmann
Frequency C la sse s
o f M easurem ents
(A b sc issa )
2 .4 3 - 2*52 mm.
2 .5 3 - 2 .6 2
2 .6 3 - 2 .7 2
2 .7 3 - 2 .8 2
2 .8 3 - 2 .9 2
2 .9 3 - 3*02
3 .0 3 - 3 .1 2
3 .1 3 - 3 .2 2
3 .2 3 - 3 .3 2
3 .3 3 - 3 .4 2
3 .4 3 - 3 .5 2
3 .5 3 - 3 .6 2
3 .6 3 - 3 .7 2
3 .7 3 - 3 .8 2
3 .8 3 - 3 .9 2
D is t r i b u t i o n
(O rd in a te )
1
0
1
1
7
8
20
20
4
it^«j»
7
4
5
5
3
«
Graph
7
G am b u a /a p a n u c o p a n u c o
2 .4 5
2 .6 5
2B 5
3 .0 5
3 .2 5 3 .4 5
3 .6 5
Hubbs
3 .8 5
Gr a ph 8
A 7/cropoec///a
d r a n n e r / Ei ge nma nn
GRAPH 9
Xxphophorus h e l l e r i i H eckel
F requency C la sse s
o f M easurem ents
(A b sc issa )
2 .4 2
2 .5 1 mm.
2 .5 2
2 .6 1
2 . 6 2 - 2 .7 1
2 .7 2 - 2 .8 1
2 .8 2 - 2 .9 1
2 .9 2 - 3 .0 1
3.0 2 - 3 .1 1
3.1 2 - 3.2.1
3*22 - 3 .3 1
3-32 - 3*41
3*42 - 3 .5 1
3.5 2 - 3 .6 1
3.6 2 - 3 .7 1
3-72 - 3 .6 1
3 .6 2
3 .9 1
3 .9 2 - 4 .0 1
-
-
-
D is tr i b u t i o n
(Ordi]
1
4
3
10
14
9
11
7
11
11
9
3
3
1
2
1
GRAPH 10
Gambusia a f f i n i s h o lb ro o k ii G ira rd
2 .5 1
2 .6 1
2 .7 1
2 .8 1
2 .9 1
3 .0 1
3 .1 1
3.2.1
3 .3 1
3 .4 1
3 .5 1
3 .6 1
3 .7 1
3 .3 1
3 .9 1
-
2 .6 0 mm.
2 .7 0
2 .8 0
2 .9 0
3 .0 0
3 .1 0
3 .2 0
3 .3 0
3.40
3 .5 0
3.60
3.70
3 .3 0
3.90
4 .0 0
2
3
6
9
13
11
10
15
11
2
11
2
■2
2
1
23
21
Graph 9
19
X /p h o p h o r u s h e lle rii H e c k e l
17
15
13
II
9
7
5
3
I
2 .4 2
2 .6 2
2 .8 2
3 .0 2
3 .2 2
3 .4 2
3 .6 2
3 .8 2
23
21
Graph
19
10
G a m b u a /a a f f / n / s b o /b r o o k //
Gi r a r d
17
15
13
II
9
7
5
3
I
~i
i ii l I I I I i i I l
Z.5I 2 7 1
2.91
3-11
3.31
3.51
3.71
I il i I I l I 1 I i I I I l I I l I I
3.91
GRAPH 11
B ra e h y rh a p h is
e p is c o p i S te in d a e b n e r
F req u en cy C la s se s
o f M easurem ents
(A b sc issa )
2 .4 2 - 2 .5 1 nnu’
2 .5 2 - 2 .6 1
2 .6 2 - 2 .7 1
2 .7 2 - 2 .8 1 ,
2 .8 2 - 2 . 9 !
2 .9 2 - 3-01
3 .0 2 - 3 .1 1
3 .1 2 - 3 -2 1
3 .2 2 - 3-31
3-32 - 3-41
3 .4 2 - 3-51
3-52 - 3-61
3 -6 2 - 3 .7 1
3-72 - 3*81
3 .8 2 - 3 .9 1
3 .9 2 - 4-01
D i s tr i b u t i o n
(O rd in a te )
1
7
10
12
10
9
6
9
8
7
8
4
3
1
2
3
GRAPH 1 2
P l a t y p o e c i l u s m a c u la tu s G u e n th e r
Frequency C la s se s
o f M easurem ents
(A b sd ssa )
2 .3 1 - 2 .4 0
2 . 4a - 2 .5 0
2 .5 1 - 2 .6 0
2 .6 1 - 2 .7 0
2 .7 1 - 2 .8 0
2 .8 1 - 2 .9 0
2 .9 1 - 3 -0 0
3 -0 1 - 3 .1 0
3-11 - 3 -2 0
3 -2 1 - 3*3®
3 .3 1 - 3 ,4 0
3 -41 - 3-50
3 -51 - 3 -6 0
3 -61 - 3-70
3 -71 - 3*80
3 .8 1 - 3-90
D is trib u tio n
(O rd in a te )
2
2
2
1
7
9
11
9
17
12
6
7
7
4
3
1
G r a p h
B ra e h y rh a p h is
II
e p is c o p i S t e i n d a c h n e r
2.42 Z.6Z 2.82 3.02 3.22 3.42 3.62 3.82 4.02
\Z
m a c u ia tu s G u e n t h e r
Graph
P /a ty p o e c i/u s
GRAPH 13
Lim ia v i t t a t a G uichenot
F requency C la s se s
o f M easurem ents
(A b sc issa )
2 .6 3 - 2 .7 2 mm.
2 .7 3 - 2 .8 2
2 .8 3 - ‘2 .9 2
2 .9 3 - 3 .0 2
3 .0 3 - 3 .1 2
3 .1 3 - 3 .2 2
3.2 3 - 3*32
3 .3 3 - 3-4-2
3.A3 - 3 .5 2
3 .5 3 - 3 .6 2
3 .6 3 - 3 .7 2
3*73 and o v er
D istr ib u tio n
(O rd in a te )
3
5
9
9
8
22
13
9
5
6
7
3
GRAPH 14
M o llie n is ia p e te n e n s is Hubbs
F requency C la sse s
o f M easurem ents
(A b sc issa )
2 .7 9 - 2 .8 8 mm.
2 .8 9 - 2 .9 8
2 .9 9 - 3*08
3 .0 9 - 3 .1 8
3 .1 9 - 3 .2 8
3 .2 9 - 3 .3 8
3 .3 9 - 3 .4 8
3-49 - 3 .5 8
3 .5 9 - 3 .6 8
3 .6 9 - 3 .7 8
3 .7 9 - 3 .8 8
3 .8 9 - 3 .9 8
3.9 9 - 4 .0 8
4 .0 9 - 4 .1 8
4 .1 9 and o v er
D is tr ib u tio n
(Ordi:
1
1
7
10
14
13
14
7
9
9
7
1
3
2
2
23
Graph
21
19
L im ia
13
vitta ta
G uichenot
17
15
13
II
9
7
5
3
I
I I I I I 1 I I I M
I I I I
2.63 2.83 3.03 3.23 3.43 3.63 3.83
I
I
I I
I
I
I
I
11
I I
I I
I
I
1 1
23
G r a p h 14
21
19
M o N /e n i a ia
p e t e n e n s/s
Hubbs
17
15
13
II
9
7
5
3
1
i I I I I I I I I I I 1 I..I I I I I L I L I
2.79 2.99 3.19 3.39 3.59 3.79 3.99 4.19
11
I I I
I I I I I I
GRAPH 15
G lary d ich b h y s f a l c a t u s Eigenmann
F requency C la s se s
o f M easurem ents
(A b sc issa )
2 .5 2 - 2 .6 1
2 .6 2 - 2 .7 1
2 .7 2 - 2 .8 1
2 .8 2 - 2 .9 1
2 .9 2 - 3 .0 1
3 .0 2 - 3 .1 1
3 .1 2 - 3 *2.1
3 . 2.2 - 3 .3 1
3*32 - 3 .4 1
3 .4 2 - 3 .5 1
3 .5 2 - 3 .6 1
3 .6 2 - 3 . 7 1
D i s tr i b u t i o n
(O rd in a te )
3
4
13
9
17
17
17
4
6
6
2
2
GRAPH 16
H e te ra n d ria form osa A g assiz
Frequency C la s se s
o f M easurem ents
(A b sc issa )
2 .% - 2 .8 5 mm.
2.86 - 2 .9 5
2.9 6 - 3.05
3.06 - 3.15
3.16 - 3 .2 5
3.26 - 3 .3 5
3.3 6 - 3.45
3.46 - 3 .5 5
3.5 6 - 3-65
3.6 6 - 3-75
3.7 6 - 3-85
3.86 - 3 .9 5
3.96 - 4 .0 5
D is tr i b u t i o n
( O rd in at
1
5
13
11
17
18
10
7
2
9
2
2
3
,
z
23
Gr a ph 15
21
G /a rycf/ch th ya
19
fa / c a t u s E i g e n m a n n
17
15
13
II
9
7
5
3
I
2.52 2.72 2.92 3.12 3.32 3.52 3.72
23
21
Graph
19
H e te r a n d r /a
16
formosa
A g a ssiz.
17
15
13
II
9
7
5
3
I
I I I 1 I I 1 I I 1 I I I I I I 1 1 1 I 1 I I 1 1 - I— I— 1 - 1
2.76 2.96 3.16 3.36 3.56 3.76 3.96
1
GRAPH IS
D i s t r i b u t i o n o f S p e c ie s w ith R esp ect t o S i g n if ic a n t T e s ts
S = S ig n ific a n t
ISA
No. o f S T e s ts
(O rd in a te )
S p e c ie s Niambers
(A b sc is sa )
T e s ts w it b in D i s tr i b u t i o n Oromp
•
2
3 - 6 - 12 - 16 - 2 0 -2 1
Not s i g n i f i c a n t w ith one
a n o th e r (T ab le 5)
3
5- 9 - I I - I 3 - I 9
Not S w ith one a n o th e r (T a b le 6 ]
4
10
-------------- ---------
5
1 5 -1 8 -4
15 and 18 n o t S w ith one
a n o th e r .
4 i s S w ith 15 and 18 (T ab le 7)
6
1 -8
Not S w ith one a n o th e r (T ab le 7]
9
2
—
1 4 -1 7
S w ith one a n o th e r (T a b le 7)
19
-----:
-------------------- —
18B
2
3 -6 -1 2 -1 6 -2 0 -2 1
Not S w ith one a n o th e r (T ab le 5!
3
9 -1 1 -1 3 -1 9
Not S w ith one a n o th e r (T ab le 6]
4
10
5
15
6
8
9
2
19
—
—
—
_ —
14
18C
3
5
5
4 -1 8
L
O
JL
19
17
S w ith one a n o th e r (T a b le 7)
-------------------
1
1
Distribution
of
Species with
A.
Respect to Significant Tests
D i s t r i b u t i o n for All Twenty
Speci es
ILI IIIIIIIIIIIIlIIIII
IIIIIII1 II1
14 17 2
I 4 15 10 5 3
8
18
9 6
II \Z
13 (6
19 ZO
Z\
19
17
B.
C. S p e c i e s with Com
pound H e t e r o c h r o m o
som es
S p e c i e s with Two
He t e r o c h r o mo s o me s
13
II
9
7
5
3
1 .1 .1
14 2 8 15 10 9 3
II 6
17
I
1 18 4
13 \Z
19 16
20
Z\
G r a p h 18
1,
5
GRAPH 17
Q u in tan a a tr iz o n a Hubbs
F requency C la s se s
o f M easurem ents
(A b sc issa )
2 .3 9 - 2 .4 8 mm.
2 .4 9 - 2 .^ 8
2 .5 9 - 2 .6 8
2 .6 9 - 2 .7 8
2 .7 9 - 2 . a s
2 .8 9 - 2 .9 8
2 .9 9 - 3 .0 8
3.0 9 - 3 .1 8
3 .1 9 - 3 .2 8
3 .2 9 - 3 .3 8
3 .3 9 - 3 .4 8
3.4 9 - 3 .5 8
D istr ib u tio n
(O rd in a te )
4
3
1
11
15
17
18
15
8
4
3
1
GRAPH 19
G ira rd in u s m e ta lllc u s Poey
Frequency C la s se s
o f M easurem ents
(A b sc issa )
2 .3 4 - 2 .4 3 mm.
2 .4 4 - 2 .5 3
2 .5 4 - 2 .6 3
2 .6 4 - 2 .7 3
2 .7 4 - 2 .8 3
2 .8 4 - 2 .9 3
2 .9 4 - 3 .0 3
3 .0 4 - 3 .1 3
3 .1 4 - 3 .2 3
3.2 4 - 3 .3 3
3 .3 4 - 3 .4 3
3-44 - 3 .5 3
3 .5 4 - 3 .6 3
3 .6 4 - 3 .7 3
3 .7 4 - 3 .8 3
3-84 - 3 .9 3
3 .9 4 - 4 .0 3
4 .0 4 - 4 .1 3
4 .1 4 - 4 .2 3
4 .2 4 - 4 .3 3
4 .3 4 - 4 .4 3
4 .4 4 - 4 .5 3
4.54 - 4 .6 3
4 .6 4 - 4 .7 3
4 .7 4 - 4 .8 3
4 .8 4 - 4 .9 3
4 .9 4 - 3 .0 3
5 .0 4 - 3 .1 3
5.1 4 and o v er
D is tr i b u t i o n
(O rd in a te )
2
1
4
11
10
6
6
9
13
5
8
7
10
10
8
9
4
5
1
3
2
4
1
3
1
0
2
1
2
Z3
21
Gr aph 17
Q u /n ta n a
19
a tr /z o n a Hubba
17
15
13
II
9
7
5
3
I
1.l-l.i-jJ .-UL
J I U LI J L U .1.1.1 I. IJ.L L 1 J
2.39 2.59 2.79 2.99 3.19 3.39 3.59
23
2!
Graph
19
19
G ira rcf/n u s m e t a / / / c u a
Poey
17
15
13
II
9
7
5
3
I
2.34 2.54 2.74 2.94 3.14 3.34 3.54 3.74 3.94 4.14 4.34 4 5 4 4.74 4.94 534
GRAPH 20
P o e c i l i o p s i s in f a n s Hubbs
F requency C la sse s
o f M easurem ents
(A b sc issa )
2 .4 6 - 2 .5 5 ram.
2 .5 6 - 2 .6 5
2 .6 6 - 2 .7 5
2 .? 6 - 2 .8 5
2 .8 6 - 2 .9 5
2 .9 6 - 3 .0 5
3.06 - 3-15
3.16 - 3 .2 5
3.26 - 3 .3 5
3.36 - 3 .4 5
3.46 - 3 .5 5
3.56 - 3.65
3.6 6 and over
D istrib u tio n
(O rd in a te )
3
5
8
20
17
20
18
24
11
11
4
7
2
GRAPH 21
M o llie n is ia l a t i p i n n a LeSueur
Frequency C la sse s
o f M easurem ents
(A b sc issa )
2 .6 9 - 2 .7 3 mm.
2 .7 4 - 2 .7 8
2 .7 9 - 2 .8 3
2 .8 4 - 2 .8 8
2 .8 9 - 2 .9 3
2 .9 4 - 2 .9 8
2 .9 9 - 3 .0 3
3 .0 4 - 3 .0 8
3 .0 9 - 3 .1 3
3 .1 4 - 3 .1 8
3.1 9 - 3 .2 3
3.2 4 - 3-28
3 .2 9 - 3 .3 3
3 .3 4 - 3 .3 8
3*39 - 3 .4 3
3 .4 4 - 3 .4 8
3 .4 9 - 3 .5 3
3 .5 4 - 3 .5 8
3 .5 9 - 3 .6 3
3 .6 4 - 3 .6 8
3 .6 9 - 3 .7 3
3*74 and o v er
D i s tr i b u t i o n
(O rd in a te )
2
2
4
3
3
3
6
10
8
19
15
12
16
12
9
5
8
2
5
2
2
2
23
Graph 2 0
P o e c /7 / o p s / j Jnfan^
19
Hubbs
17
15
13
II
9
7
5
3
2 .4 6
2 .6 6
ZB6
3 .0 6
3 .2 6
3 .4 6 3 .6 6
23 r
21
19
17
Graph 2 1
P7o///er?5/a /a tip /n n a
Le S u e u r
GRAPH 22
P la ty p o e c ilu s v a r i a t u s Meek
F req u en cy C la s se s
o f M easurem ents
(A b sc issa )
2 .2 9 - 2 .3 8 mm.
2 .3 9 - 2 .1 8
2.A9 - 2 .5 8
2 .5 9 - 2 .6 8
2 .6 9 - 2 .7 8
2 .7 9 - 2 .8 8
2 .8 9 - 2 .9 8
2 .9 9 - 3 .0 8
3 .0 9 - 3 .1 8
3 .1 9 - 3.2.8
3.2-9 - 3 .3 8
3 .3 9 - 3 .1 8
3-19 - 3 .5 8
3 .5 9 - 3 .6 8
3 .6 9 - 3*78
3 .7 9 - 3 .8 8
3 .8 9 - 3 .9 8
3 .9 9 - 1 .0 8
1 .0 9 - 1 .1 8
1 .1 9 - 1* 28
1 .2 9 - 1 .3 8
1 .3 9 - 1* 18
D i s tr ib u tio n
(Ordi]
2
0
1
3
3
7
10
15
20
17
18
u
13
9
5
2
1
1
0
1
1
1
GRAPH 23
P o e c i l i s t e s p le u r o s p ilu s G uenther
Frequency C la s se s
o f M easurem ents
(A b sc issa )
2.2-7 - 2 .3 6 mm.
2 .3 7 - 2 .1 6
2 .1 7 - 2.56
2 .5 7 - 2 .6 6
2 .6 7 - 2 .7 6
2 .7 7 - 2.86
2 .8 7 - 2 .9 6
2 .9 7 - 3.06
3 .0 7 - 3 .1 6
3 .1 7 - 3*2.6
3 .2 7 - 3-36
3 .3 7 - 3-16
3 .1 7 - 3.56
3 .5 7 - 3 .6 6
D is trib u tio n
(O rdii
1
1
9
22
21
17
21
23
20
17
20
11
1
1
23
21
Graph 22
P /a ty p o ec //u s
19
variatua M e e k
17
15
13
il
9
7
5
3
I
2 .2 9
2 .4 9
2 .6 9 2 .8 9
3 .0 9
3 .2 9
3 .4 9
3 .6 9
3 .8 9 4 . 0 9
4 .2 9
23
G r a p h
21
P o e c ///a t e a
19
17
15
13
II
9
7
5
3
I
2.27 2.47 2.67 2.87 3.07 3.27 3.47 3.67
2 3
p / e u r o a p i !ua G u e n t h e r
VITA
Name:
J e a n C ra ig K r a ft
P la c e o f B ir th :
C hicago, I l l i n o i s , June 2 , 190S
E d u c a tio n :
U n iv e r s ity o f Chicago High S ch o o l, 1922-1926, Diploma 1926
U n iv e r s ity o f W isconsin, M adison, W isconsin, 1926-1927
N o rth w este rn U n iv e r s ity , E v an sto n , I l l i n o i s , 1927-1930,
B. S ., 1930
N o rth w este rn U n iv e r s ity , G raduate S chool, 1930-1931*
Summer 1931* F i r s t S em ester 1931-1932,
M. A. 1932
N o rth w e stern U n iv e r s ity , G raduate S chool, 1931-1910
M arine B io lo g ic a l S ta t io n , Woods H ole, M a ss a c h u se tts ,
Simmer, 193 7
P o s i t i o n s H eld:
G rad u ate A s s i s ta n t, N o rth w estern U n iv e r s ity , 1930-1931*
Second S em ester, 1939-1910; G raduate F e llo w sh ip ,
1938-1939
O th e r D ata:
Sigma D e lta E p s ilo n , 1930
A s s o c ia te M embership, Sigma X i, 1935
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