Question

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: Rose crossed with pea produces 20 walnut 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

Answer 1

For a rose x pea cross to produce walnut offspring, the rose comb chicken must have genotype Rr pp, and the pea comb chicken must have genotype rr Pp.

Step-by-step explanation:

The question is about determining the genotypes of chicken parents based on the phenotype of their offspring. Comb shapes in chickens are influenced by genes at two loci (R, r and P, p). The cross described is between a rose comb and a pea comb chicken which resulted in walnut comb offspring. To have walnut offspring, each must contribute at least one dominant allele R and P respectively.

The rose comb parent must have a genotype which contributes the dominant R allele and recessive pp alleles, so its genotype is Rr pp. The pea comb parent must contribute the rr genotype from locus one and at least one dominant P from the second, which is rr Pp. Therefore, we can infer that a rose comb parent with genotype Rr pp was crossed with a pea comb parent with genotype rr Pp to produce walnut comb offspring.

Answer 2

in the obtained options, there is no dominant gene for the crossed pairs, therefore, no answer would be correct, however, when assigning a dominant character to the P gene, the correct answer would be:

E. Rr pp *rrPp

Step-by-step explanation:

According to the information obtained we deduce:

Comb shape is produced by R and P

Comb of walnuts with an R or a P

Pink comb: 1 dominant P and R at the first locus and 2 recessive at the next locus

Pea comb: 2 recessive at the start and one dominant in the next position

1 single comb: 2 recessive at both loci

Rr pp × rr Pp will produce from the interbreeding: 2 walnuts, 1 single and 1 pea offspring.

We deduce that for the pink comb the genotype is: Rrpp

and for the pea comb it is rrPp

Rr pp × rr Pp generates crosslinks containing RrPp, rrPp, rrpp as children in a 2: 1: 1 ratio.