Question

A farmer bred two horses. One had a homozygous genotype and had white hair, the other had a homozygous genotype and had black hair. The resulting offspring had a roan coat, with both white and black furs showing equally. What is the explanation for how the offspring had the roan coat?(1 point)
Responses

The allele for white hair must be completely dominant to the the allele for black hair.
The allele for white hair must be completely dominant to the the allele for black hair.

The alleles must show incomplete dominance.
The alleles must show incomplete dominance.

The allele for roan hair is found on the X chromosome and therefore is a sex linked trait.
The allele for roan hair is found on the X chromosome and therefore is a sex linked trait.

The allele for white hair must be codominant with the allele for black hair.
The allele for white hair must be codominant with the allele for black hair.

Answer 1

The allele for white hair must be codominant with the allele for black hair.

Explanation: In codominance, heterozygotes express both parental phenotypes simultaneously (roan = both white and black hairs). Incomplete dominance would give a blended intermediate, and complete dominance or sex linkage do not explain equal expression of both colors.