Rose Rooster

Guessing genotypes…?

In chickens, two genes interact to produce four different comb phenotypes. Suppose a true breeding walnut comb rooster (PPRR) mates with a true breeding single comb chicken (pprr). One of the male offspring then mates with a pea comb chicken. One of their offspring has a rose comb. What is the most likely genotype of the mother?

Answer: Pprr
Reasoning: I am assuming P is the dominant allele over p, and R dominant over r. It is given that having both a P and R allele causes a walnut phenotype and having neither causes a single comb phenotype, and that there are only four phenotypes. It is reasonable to infer that having only P and no R (PPrr and Pprr) causes the Pea phenotype and having only R and no P (ppRR and ppRr) causes the Rose phenotype. All offspring from the PPRR x pprr breeding is PpRr (walnut). The chicken breeding with this offspring is Pea so either Pprr or PPrr. PpRr x PPrr would always have a P allele and thus couldn’t be a Rose phenotype. Alternatively, if the mother is Pprr then the offspring has a 25% chance of being ppRr which is the Rose phenotype we were looking for. Ergo, mother is Pprr.

15 • I’ll Still Be Loving You – Kennedy Rose at the Red Rooster Benefit / Tribute to Todd Cerney