Hardy-Weinberg Equilibrium Problem

Question

If 75 individuals of 735 have the homozygous dominant genotype for a phenotypic trait, what is the allelic frequency for that trait among those individuals?

Answer options: 0.01, 0.75, 0.1, 0.46, 0.35

I did 75/735 and got 0.102, and then took the square root of that which is 0.319, which isn't an option... what am I doing wrong?

Answer 1

You started off great! The Hardy-Weinberg equation is p² + 2pq + q² = 1 where p² is the allelic frequency for the homozygous dominant genotype, 2pq is the allelic frequency of the heterozygous genotype, and q² is the allelic frequency for the homozygous recessive genotype. All you have to do is divide the number of individuals with the homozygous dominant genotype by the total population, just like you already did. 75/735 = 0.102 which is your frequency, so the answer is 0.1. p² is the frequency, so there is no need to take the square root of your answer. Hope that helps! :)