Chi-Square/Hardy Weinberg

Question

The frequency of a homozygous dominant genotype is 0.49.

What is the frequency of the dominant allele?

Is this meant to use p+q = 1?

What is the frequency of the homozygous recessive genotype?

Would this use p²+2pq+q²=1?

Answer 1

When looking at genotypes and their frequency in a population, you will be using the p² + 2pq + q² = 1 equation. When solving for the frequency of alleles, you will be using the p + q = 1 equation. So, for this problem you are given the frequency of the homozygous dominant genotype, p². Therefore, to solve for p, we take the square root of 0.49, which is 0.7. Now that we have p, we can solve for q via 1 - 0.7 = q = 0.3. Now that we have the allele frequency for both the dominant and recessive allele, we can solve for the frequency of the homozygous recessive genotype, q² = 0.3² = 0.09.

What is important to remember when solving these problems is whether you have been given the frequency of the allele or genotype, and then using the Hardy-Weinberg principle to solve for whatever your question is asking for.