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 = 0.95, w_aa = 0.9

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 \(p + q = 1\), which is true here.
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 after one generation using: \(p' = f'(AA) + \frac{1}{2} f'(Aa)\) and \(q' = f'(aa) + \frac{1}{2} f'(Aa)\).

Key Concepts

Allele Frequency

Allele frequency refers to how common a particular allele is in a population, expressed as a proportion or percentage. In this question, p and q represent the frequencies of alleles A and a, respectively, and their sum must equal 1. Understanding allele frequencies is essential for predicting genetic variation over generations.

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 or recessiveness, neither allele masks the other. This affects how genotype frequencies translate into phenotypes and fitness values.

Fitness and Selection Coefficients

Fitness (w) measures the reproductive success of a genotype relative to others, influencing allele frequency changes through natural selection. Here, different fitness values for AA, Aa, and aa genotypes indicate selection pressures that alter allele frequencies in the next generation. Calculating post-selection frequencies requires weighting genotypes by their fitness.