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# How to Solve a Punnet Square

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```﻿How to Solve a Punnet Square
1. Determine the genotypes (letters) of the parents. Bb x Bb
2. Set up the Punnet square with one parent on each side.
3. Fill out the Punnet square middle
4. Analyze the number of offspring of each type.
In pea plants, round seeds are dominant to wrinkled. The genotypes and phenotypes are:
RR = round
Rr = round
rr = wrinkled
If you get stuck make a "key". Sometimes the problems won't give you obvious information. Example: In radishes, a bent root is a dominant trait, though some roots are straight (which is recessive). If a straight rooted plant is crossed with a heterozygous bent root plant, how many of the offspring will have straight roots?
Say what? First of all, this problem doesn't make it easy. Start by assigning genotypes and phenotypes. Pick the letter of the dominant trait. B for bent
BB = bent
Bb = bent
bb = straightNow use the key to figure out your parents. In this case you have a straight root plant (bb) crossed with a heterozygous bent plant (Bb). Once you've figured that out, the cross is simple! If a heterozygous round seed is crossed with itself (Rr x Rr) a punnett square can help you figure out the ratios of the offspring.
3/4 round, 1/4 wrinkled
```
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