Epistasis and Chicken Combs

abracadabra1

Diamond Member
Nov 18, 1999
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Genetics Question

Parents

ppRR (rose comb) PPrr (pea comb)

Offspring

PpRr (walnut comb)

permitted to interbreed amongst one another

Yields 9:3:3:1 ratio (Walnut:pea:rose:single)

Can anyone help me in identifying the pathway that permits the 2 enzymes that arise from genes P and R (when functional) that produce a walnut comb.

e.g. Single comb ----- Enzyme A (P functional)---> rose comb ------------Enzyme B (R functional)----> walnut comb

This given pathway of course doesn't yield the correct results because should p be non-functional, yet R be functional, then the rose comb phenotype still arises. Also, the same is true should the two genes be reversed (e.g. functional P and nonfunctional R). P and R need to be functional in order for walnut comb to arise.

Any ideas fellas?