In chickens, comb shape is determined by genes at two loci (R, r and P, p).A walnut comb is produced when at least one dominant gene R is present at one locus and at least one dominant gene P is present at a second locus (genotype R_ P_).A rose comb is produced when at least one dominant gene is present at the first locus and two recessive genes are present at the second locus (genotype R_ pp).A pea comb is produced when two recessive genes are present at the first locus and at least one dominant gene is present at the second (genotype rr P_).If two recessive genes are present at the first and the second locus (rr pp), a single comb is produced.Give genotypes for comb shape of the parents in the following cross: pea crossed with single produces one single offspring.

Question

Quizplus · Accepted Answer

The pea comb genotype is rr P_ (requiring at least one dominant P), and the single comb genotype is rr pp (requiring two recessive p alleles). Since the offspring is single (rr pp), one parent must contribute the rr genotype and at least one p allele, and the other must contribute the other p allele. The only option that fits this description is E) rr Pp × rr pp, where one parent has the pea comb genotype (rr Pp) and the other has the single comb genotype (rr pp).

In Chickens, Comb Shape Is Determined by Genes at Two