SBI 3U Incomplete Dominance Codominance

Mendel’s experiments illustrate complete dominance - offspring always resembled one of the two parents The dominant allele had the same phenotypic effect whether present in one or two copies All Mendel’s plants displayed dominant or recessive alleles. In other words, only one trait showed up.

Genetics After Mendel (exceptions)

Incomplete Dominance heterozygous individuals have an intermediate phenotype neither of the alleles is dominant because they do not mask the other colour Example flower colour: – Phenotype: Red flowers x White flowers  Pink flowers – Genotype: C R C R x C W C W  C R C W

Questions: Incomplete Dominance 1. What are the phenotypic and genotypic ratios for the F 1 and F 2 generation of a cross between and white and red snap dragon? 2. Indicate the ratios that would be expected if the following crosses are made: a) red x pink b) white x white c) pink x pink

Codominance both alleles are expressed fully to produce offspring with a third mixed phenotype Example cows skin colour – Phenotype: White cow x Red cow  Roan cow (red & white mix) – Genotype: H w H w x H r H r  H w H r

A red bull (without wings!!!) is crossed with a white cow. What is the F 1 genotype and phenotype ratios?