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?
wAA=1, wAa=0.9, waa=0.8

Verified step by step guidance

1. Identify the initial allele frequencies: \(p = 0.7\) for allele A and \(q = 0.3\) for allele a. Since \(p + q = 1\), these represent the starting frequencies before selection.
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., \(w_{AA} = 1\), \(w_{Aa} = 0.9\), and \(w_{aa} = 0.8\).
4. Calculate the mean fitness of the population, \(\bar{w}\), by summing the weighted genotype frequencies: \(\bar{w} = f(AA) \times w_{AA} + f(Aa) \times w_{Aa} + f(aa) \times w_{aa}\).
5. Determine the new allele frequencies after selection by calculating the contribution of each genotype to allele A and allele a, then normalize by dividing by the mean fitness \(\bar{w}\). For allele A, use: \(p' = \frac{f(AA) \times w_{AA} + \frac{1}{2} f(Aa) \times w_{Aa}}{\bar{w}}\). For allele a, use: \(q' = \frac{f(aa) \times w_{aa} + \frac{1}{2} f(Aa) \times w_{Aa}}{\bar{w}}\).

Key Concepts

Allele Frequencies and Hardy-Weinberg Principle

Allele frequencies represent the proportion of different alleles in a population's gene pool. The Hardy-Weinberg principle predicts genotype frequencies from allele frequencies under no evolutionary forces. Understanding initial allele frequencies (p and q) is essential to track changes after selection.

Codominance

Codominance occurs when both alleles in a heterozygote are fully expressed, producing a distinct phenotype for heterozygotes. This affects how genotypes contribute to fitness and how selection acts on each genotype, influencing allele frequency changes.

Fitness and Selection Coefficients

Fitness values (w) measure the reproductive success of genotypes. Selection alters allele frequencies by favoring genotypes with higher fitness. Calculating post-selection allele frequencies requires weighting genotype frequencies by their fitness and normalizing.