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28 March, 04:40

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

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Answers (2)
  1. 28 March, 05:34
    0
    B) Rr pp * rr Pp

    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.
  2. 28 March, 06:26
    0
    Option B, Rr pp * rr Pp

    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
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