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_). What will be the phenotypic ratio if a cross is made between a female who is pp RR and a male who is PP rr
If a cross is made between a female who is RRpp (rose comb) and a male who is rrPP (pea comb) then:
P: RRpp x rrPP
F1: RrPp RrPp RrPp RrPp
This means that all of the offspring in F1 generation will have heterozygous genotype (at both loci). Since it contains both dominant alleles, the phenotype is walnut comb.
