Final answer:
In the F2 generation of a cross between rose and pea comb chickens, the phenotypic ratio is expected to be similar to Mendel's 9:3:3:1 phenotypic ratio derived from a dihybrid cross.
Step-by-step explanation:
The expected phenotypic ratio in F2 when rose comb chickens (R_pp) and pea comb chickens (rrP_) are crossed to produce walnut comb F1 offspring is a result of the interaction of two genes determining comb shape in chickens. Assuming that the rose comb is produced by at least one dominant allele R and no dominant allele P (R_pp), and the pea comb is produced by at least one dominant allele P and no dominant allele R (rrP_), and that walnut is the result of having at least one dominant R and one dominant P allele (R_P_), the cross can be represented as a dihybrid cross similar to that of pea plants. Using the principles of independent assortment and dominance, this will lead to a phenotypic ratio resembling a 9:3:3:1, just as in Mendel's dihybrid cross for seed color and texture in pea plants.