The answer is C Multiple alleles for feather color are present in the population.
An allele is one of two or more alternative forms of a gene. Since feather color in a bird was traced to a single gene, the trait is a monogenic and not a polygenic trait (choice b drops off). Further, there are 6 variations of feather color which are controlled by one gene. That means there are 6 variations of the gene. And since the alleles are alternative forms (or variations) of the gene, there are 6 different alleles for feather color.
