Consider a population in which the frequency of allele A is p = 0.7 and the frequency of allele a is q = 0.3 and where the alleles are codominant. What will be the allele frequencies after one generation if the following occurs?
w_AA = 1, w_Aa = 0.99, w_aa = 0.98

Verified step by step guidance

1. Identify the initial allele frequencies: \(p = 0.7\) for allele \(A\) and \(q = 0.3\) for allele \(a\). Confirm that \(p + q = 1\).
2. Calculate the initial genotype frequencies assuming Hardy-Weinberg equilibrium: \(f(AA) = p^2\), \(f(Aa) = 2pq\), and \(f(aa) = q^2\).
3. Apply the given fitness values to each genotype to find the weighted genotype frequencies after selection: multiply each genotype frequency by its respective fitness, i.e., \(f'(AA) = f(AA) \times w_{AA}\), \(f'(Aa) = f(Aa) \times w_{Aa}\), and \(f'(aa) = f(aa) \times w_{aa}\).
4. Calculate the mean fitness of the population, \(\bar{w}\), by summing the weighted genotype frequencies: \(\bar{w} = f'(AA) + f'(Aa) + f'(aa)\).
5. Normalize the weighted genotype frequencies by dividing each by \(\bar{w}\) to get the genotype frequencies after selection. Then, calculate the new allele frequencies: \(p' = f'(AA) + \frac{1}{2} f'(Aa)\) and \(q' = f'(aa) + \frac{1}{2} f'(Aa)\).

Key Concepts

Allele Frequency

Allele frequency refers to how common an allele is in a population, expressed as a proportion or percentage. In this question, p = 0.7 for allele A and q = 0.3 for allele a, meaning 70% and 30% of the alleles in the gene pool are A and a, respectively. These frequencies are the basis for predicting genotype frequencies and evolutionary changes.

Codominance

Codominance occurs when both alleles in a heterozygote are fully expressed, resulting in a phenotype that shows traits of both alleles simultaneously. Unlike dominance/recessiveness, neither allele masks the other. This affects how genotype fitness values influence allele frequency changes in the population.

Fitness and Selection Coefficients

Fitness (w) measures the reproductive success of a genotype relative to others. Here, w_AA = 1, w_Aa = 0.99, and w_aa = 0.98 indicate slight differences in survival or reproduction. These differences cause natural selection, altering allele frequencies over generations by favoring genotypes with higher fitness.