Which genotype crossed with a rose comb chicken results in a progeny of 50% walnut comb and 50% pea comb?

The correct choice is the genotype that produces a 50% walnut comb and 50% pea comb offspring, which is rrPP.

In chickens, comb shape is determined by multiple genes, with at least two genes involved—one gene represents the walnut comb and another represents the pea comb. The walnut comb phenotype is typically dominant over the pea comb, and both of these phenotypes can be expressed when certain combinations of alleles are present.

When the genotype rrPP is crossed with a rose comb chicken (which can be either a homozygous or heterozygous genotype for the rose comb trait), the resulting gametes from rrPP would only contribute r (which is recessive and does not affect the comb shape from the walnut) and P alleles. The rose comb chicken can contribute either R or r and P or p alleles depending on its own genotype.

In this specific cross, the rrPP would consistently provide a homozygous dominant allele for the P trait, which dictates walnut comb formation. If the rose comb chicken is heterozygous for this trait (RrPp), the offspring could include:

1. Walnut comb (from the P allele) - 50% of the combinations will have at least one