Concerning the genetics of comb shape in chickens, which statement is true?

The statement regarding the genetics of comb shape in chickens identifies the necessity of both the R (Rose) and P (Pea) genes to produce a walnut comb. This is based on the inheritance patterns for chicken comb shape, where both genes interact in a way that their dominance determines the resulting comb appearance.

A walnut comb results when at least one dominant allele from each gene is present. In this case, the presence of both dominant traits contributes to the distinct walnut shape. If only one of the genes were dominant, the resulting phenotype would be different, along the lines of either a Rose comb or a Pea comb. Thus, for a walnut comb, the expression relies on the presence of alleles from both gene loci, not just one or the absence of both.

This understanding clarifies why neither the absence of both genes nor the presence of only recessive alleles would yield a walnut comb. In summary, the requirement for two dominant alleles from both the R and P genes to form a walnut comb underscores the complexity of genetic interactions governing comb shape in chickens.