Question

17. In chickens, some varieties have feathered shanks (legs), but others do not. In a cross between a Black Langhans (feathered shanks) and Buff Rocks (unfeathered shanks), the shanks of the F1 generation are all feathered. When the F1 generation is crossed, the F2 generation contains chickens with feathered shanks to unfeathered shanks in a ratio of 15:1. Suggest an explanation for this result.

Answer 1

Feathered shanks is an example of duplicate dominant epistasis and gives F2 phenotype ratio 15:1.

Step-by-step explanation:

Presence of feathered shanks in chickens is an example of duplicate dominant epistasis. The trait is controlled by two dominant genes (A and B). Presence of at least one copy of any of these two dominant alleles results in feathered shanks. The homozygous recessive genotype (aabb) exhibits "unfeathered shanks".

Genotype of parents: Black Langhans (feathered shanks; AABB) and Buff Rocks (unfeathered shanks; aabb). F1 has genotype AaBb and crossing the F1 gives F2 chickens with feathered shanks to unfeathered shanks in a ratio of 15:1.