Incomplete Dominance Neither allele is dominant Heterozygotes are a blend of homozygous phenotypes = no distinct expression of either allele F2 phenotypic and genotypic ratios are 1:2:1 Snapdragon/Four o’clock flower color Eggplant color Tay-Sachs disease

Animation showing incomplete dominance in F1 and F2 generations

Exercise to predict ratios in situations where there is incomplete dominance

Try these In a plant species, if the B allele (blue flowers) and the W allele (white flowers) are incompletely dominant (b is light blue), what offspring ratio is expected in a cross between a blue-flowered plant and a white-flowered plant? What would be the phenotypic ratio of the flowers produced by a cross between two light blue flowers?

Codominance Both alleles are equally dominant Heterozygotes express both alleles = distinct expression of the gene products of both alleles can be detected MN blood group F2 genotype and phenotype ratios are 1:2:1 Genotype Phenotype LMLM M LMLN MN LNLN N

MN Blood group Codominance Animation

Try These Cattle can be red (RR = all red hairs), white (WW = all white hairs), or roan (RW = red & white hairs together. Predict the phenotypic ratios of offspring when a homozygous white cow is crossed with a roan bull. What should the genotypes & phenotypes for parent cattle be if a farmer wanted only cattle with red fur? A cross between a black cat & a tan cat produces a tabby pattern (black & tan fur together). What pattern of inheritance does this illustrate? What percent of kittens would have tan fur if a tabby cat is crossed with a black cat?