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

The question is incomplete, it lacks the main questions, those questions are:

a. What is the genotype for black chickens?

b. What is the genotype for white chickens?

c. What is the genotype for erminette chickens?

Explanation:

This question involves a gene coding for feather colour in some birds, in which the black allele (B) and white allele (W) is involved. According to the question, the gene coding for feather colour exhibits co-dominance i. e. both the black (B) and white (W) allele are expressed in a heterozygous state (BW) to form an erminette phenotype.

Hence, if the neither alleles is dominant or recessive over the other. The black phenotype will only be expressed when the genotype is BB.

The white phenotype will only be expressed when the genotype is WW

The combination of both alleles which results in the simultaneous expression of both in the erminette phenotype, will be BW genotype.