The Basics of GeneticsвЂ¦the passing of traits вЂў Our genes determine our traits or characteristics. вЂў Your genotype (Dd) or genetic makeup for a particular trait determines your phenotype (dimples) or physical appearance for that trait. вЂў Alleles are different forms that a gene may have for a single trait. For example, having dimples or not having dimples. вЂў Alleles can be represented by letters. You get one allele from each parent; thatвЂ™s why there are 2 letters. вЂў Alleles can be dominant, represented by a capital letter or recessive, represented by a lowercase letter. вЂў Homozygous (pure) = 2 of the same alleles for a trait; for example: dd or DD вЂў Heterozygous (hybrid) = 2 different alleles for a trait; for example: Dd Punnett squares and Pedigree Charts Punnett squares вЂў A chart that shows the chances or probability of a particular trait being expressed in offspring. вЂў Each box of the Punnett square represents a 25% chance for that trait being expressed. вЂў Example: Cross Tt and tt вЂў T = dominant allele = tall вЂў T = recessive allele = short вЂў The Tt and tt along the top and sides of the Punnett square are the genotypes for the parents. вЂў The genotypes for the offspring are inside of the Punnett square. Interpreting Punnett squares вЂў Remember that T is dominant over t, which is recessive. вЂў Parent 1вЂ™s genotype = tt; phenotype = short вЂў Parent 2вЂ™s genotype = Tt; phenotype = tall вЂў There is a 50% chance of producing short offspring = tt because there are 2 boxes with that trait. вЂў There is a 50% chance of producing tall offspring = Tt. Pedigree Charts (also see Pedigree notes) вЂў There are four generations shown on this pedigree chart. вЂў Squares = males and circles = females; if the shape is totally shaded then he/she has the condition; if the shape is shaded ВЅ way then he/she is a carrier for that condition. вЂў Generation I parents had 2 boys and 3 girls of which only 1 has the condition.