In some chickens, the gene for feather colour is controlled by codominance. The allele for black is and the allele for white is F W. The heterozygous phenotype is known as erminette.

Question

What is the genotype for black chickens?

What is the genotype for white chickens?

What is the genotype for erminette chickens?

If two erminette chickens are crossed, what is the probability that they would have a black chick? A white chick?

Answer 1

This is similar to your other question which dealt with incomplete dominance. Codominance is similar, but instead of an intermediate phenotpye of the two parental homozygous traits being expressed like we saw with the radish shapes, both of the parental traits are dominant and are both expressed at the same time if the genotype is one of each allele (heterozygote).

The fact that there's a heterozygous phenotype gives us a clue that neither allele is fully dominant over the other. Let's assume that erminette is something like a zebra or dalmatian pattern with both black and white. With this being said, the only way to get a fully white or black chicken is if the individual is homozygous for the white and black alleles.

The genotype for the erminette must be heterozygous. Regarding the last question, you can go through the same process as for the radishes. The erminette chickens are functionally equivalent to the oval radishes for this aspect of the problem.