In chickens, having feathers on legs is dominant to having featherless legs. In a population of 200 chickens, 128 have featherless legs. How many chickens are heterozygous for the "feathered leg" allele? Assume the population is in Hardy-Weinberg equilibrium.

64

Explanation:

Since the population is in Hardy-Weinberg equilibrium and the equilibrium is defined by the equation

p² + 2pq + q²

where the frequency of the homozygous dominant allele F (feathers on the leg) = p²,

F of homozygous (featherless legs) = q²

F of heterogyous (carrier of featherless allele) = 2pq

F (q²) = 128/200 = 0.64

q = √0.64 = 0.8

and p + q = 1

p = 1 - 0.8 = 0.2

2pq = 2 * 0.2 * 0.8 = 0.32

number of chickens that are heterozgous for the feathered leg allele = 0.32 * 200 = 64