Allele Interaction

Question

Two alleles of gene C control hair color in horses: C. and C.. Horses homozygous for allele C. are red, heterozygotes are yellow, and C. homozygotes are cream. What type of allele interaction is described?

(

a) pleiotropy

(b) complete dominance

(c) incomplete dominance

(d) codominance

Answer 1

Assuming that the yellow color is a blend between the red and the cream, this is an example of incomplete dominance. In incomplete dominance, the heterozygous phenotype is a blend of the two homozygous phenotypes.

Why isn't it the other answers?

1. A) Pleiotropy refers to the phenomenon of two traits being controlled by the same gene; only one trait, hair color, is mentioned in the questions.
2. B) In complete dominance, heterozygoes share the same phenotype as dominant homozygotes.
3. D) Codominance results in heterozygotes exhibiting a mixed third phenotype that contains traits from both alleles. A well known example is blood types: if one parent parent contributes an A allele and the other a B allele, their child's blood will be neither type A nor type B, but a mix between the two, type AB. In this example, a codominant allele interaction would result in heterzygote horses that were both red and yellow.