Which genotype would produce a single comb chicken in the F2 generation?

To determine which genotype would produce a single comb chicken in the F2 generation, it is essential to understand the genetics behind comb types in chickens. The trait for comb shape is influenced by a pair of alleles at two different loci: the R locus affects the comb type where the presence of the dominant R allele leads to a rose comb, while the pp genotype at the second locus results in a single comb.

In this context, the only genotype that results in a single comb phenotype is the "rrpp" genotype. The "rr" means that there are two recessive alleles for the R locus, eliminating the possibility of a rose or pea comb associated with the dominant R allele. Additionally, the "pp" indicates that the second locus is homozygous recessive, which produces the single comb phenotype.

Other genotypes may include dominant alleles or combinations that yield different comb shapes, but only "rrpp" specifically consists of the recessive alleles at both loci, directly leading to the expression of the single comb phenotype in chickens. Thus, this genotype is the only one that guarantees the single comb appearance in the F2 generation.