In Chickens, Comb Shape Is Determined by Genes at Two

question 55

Multiple Choice

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: Walnut crossed with single produces 1 walnut, 1 rose, 1 pea, and 1 single 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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