You discover a population of guppies and find it to be at Hardy-Weinberg equilibrium with respect to the S locus.Suppose there are two alleles at this locus and that the frequency of the s allele is 0.4.Of the individuals that carry at least one s allele, what fraction are homozygotes?
A) 1/8
B) 1/6
C) 1/4
D) 1/3
E) 1/2

Question

Quizplus · Accepted Answer

In Hardy-Weinberg equilibrium, the frequency of homozygotes for the recessive allele is q^2, where q is the frequency of the recessive allele. 
Here, q = 0.4, so q^2 = 0.16. Therefore, 16% of the individuals carrying at least one s allele are homozygotes. 
To convert this into a fraction, we can write 16% as 1/6, which corresponds to answer choice C.

You Discover a Population of Guppies and Find It to Be