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Incomplete Dominance

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. Try these.

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Incomplete Dominance

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  1. 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

  2. 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?

  3. 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

  4. 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?

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