Notes 20 - Simple Dominance, Incomplete Dominance, and Codominance Some genes have alleles that are dominant and recessive, but some do not. Genes with alleles that are not dominant or recessive create more than two phenotypes.

With this type of inheritance, there can only be 2 possible phenotypes Simple Dominance – One allele of the gene is dominant, one is recessive With this type of inheritance, there can only be 2 possible phenotypes Ex. Eye color (B – non-blue eyes, b – blue eyes) BB = non-blue eyes Bb = non-blue eyes bb = blue eyes

With this type of inheritance, there are 3 possible phenotypes Incomplete Dominance – Neither allele is dominant so heterozygous organisms have a mixed phenotype With this type of inheritance, there are 3 possible phenotypes Since neither allele is dominant, lowercase letters are used to represent the genes Ex. Flower color in snapdragons (r – red flowers, w – white flowers) rr = red flowers ww = white flowers rw = pink flowers

With this type of inheritance, there are 3 possible phenotypes Codominance – Both alleles are dominant, heterozygous organisms show both traits in their phenotype With this type of inheritance, there are 3 possible phenotypes Since both alleles are dominant, uppercase letters are used to represent the genes Ex. Feather color in Erminette chickens (B – black feathers, W – white feathers) BB = black feathers WW = white feathers BW = black & white