In chickens, comb shape is determined by alleles at two loci (R, r and P, p). A walnut comb is produced when at least one dominant allele R is present at one locus and at least one dominant allele P is present at a second locus (genotype R_P_). A rose comb is produced when at least one dominant allele is present at the first locus and two recessive alleles are present at the second locus (genotype: R_pp). A pea comb is produced when two recessive alleles are present at the first locus and at least one dominant allele is present at the second (genotype: rrP_). If two recessive alleles are present at the first and at the second locus (rrpp), a single comb is produced. Progeny with what types of combs and in what proportions will result from the cross between RrPp and RrPp, a single comb is produced. Give genotypes for comb shape of the parents in the following cross: Rose crossed with pea produces 2 walnut, 1 single, and 1 pea offspring.
a) RR pp × rr PP
b) Rr pp × rr Pp
c) Rr pp × rr PP
d) RR pp × rr Pp
e) Rr pp × Rr Pp