1. 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.

2. 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

3. 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

5. 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