Question

In chickens, comb shape is determined by two independent genes (R and P). A walnut comb is produced when at least one dominant allele R is present at one gene locus and at least one dominant allele P is present at a second gene 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 rr P_). If two recessive alleles 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 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

Answer 1

B) Rr pp × rr Pp

Step-by-step explanation:

In the given question, the genotype of four shapes of comb have been provided which are:

1. Walnut comb- R_ P_

2. Rose comb- R_ pp

3. Pea comb- rr P_

4. single comb- rr pp

If a cross is made between the

Rose x pea

R_ pp x rr P_

The progenies are

single : walnut : pea

rr pp : R_ P_ : rr P_

In order to determine the missing allele of parent:

1. Recessive homozygous is taken into account

2. We known that one allele is contributed by male and one by female therefore in recessive homozygous rrpp,

3. In rr- one r is contributed by male and one by female therefore one 2 comes from rr P_ and therefore one allele will come from R_ pp.

4. In pp- one allele is contributed by the R_ pp and one allele by rr P_ therefore missin allele is p.

Thus, the genotype of the parents is- Rr pp × rr Pp.

Answer 2

Option B, Rr pp × rr Pp

Step-by-step explanation:

Given

Walnut Comb is produces when one dominant allele R is present at one gene locus and at least one dominant allele P is present at a second gene locus - R* P*

Rose Comb - at least one dominant allele is present at the first locus and two recessive alleles are present at the second locus - R* pp

Pea comb - two recessive alleles are present at the first locus and at least one dominant allele is present at the second - rr P*

Single comb - two recessive alleles are present at the first and the second locus - rrpp

Parent are rose combed and pea combed

For being rose genotype must be R* pp

and for being pea combed genotype must be rr P*

Rr pp x rr Pp

will produce

Walnut comb with genotype Rr Pp

Single comb with genotype rrpp

and pea comb with genotype rrPp

Hence, option B is correct