In a population of flowers growing in a meadow, C₁ and C₂ are autosomal codominant alleles that control flower color. The alleles are polymorphic in the population, with f (C₁) = 0.80 and f (C₂) = 0.20. Flowers that are C₁C₁ are yellow, orange flowers are C₁C₂, and C₂C₂ flowers are red. A storm blows a new species of hungry insects into the meadow, and they begin to eat yellow and orange flowers but not red flowers. The predation exerts strong natural selection on the flower population, resulting in relative fitness values of C₁C₁ = 0.30, C₁C₂ = 0.60, and C₂C₂ = 1.0.
What are the equilibrium frequencies of C₁ and C₂ if predation continues?

Verified step by step guidance

1. Step 1: Understand the problem. The question involves calculating equilibrium frequencies of two codominant alleles (C₁ and C₂) under natural selection. The relative fitness values for the genotypes (C₁C₁, C₁C₂, and C₂C₂) are provided, along with the initial allele frequencies f(C₁) = 0.80 and f(C₂) = 0.20.
2. Step 2: Recall the formula for calculating equilibrium allele frequencies under selection. The equilibrium frequency of an allele can be determined using the concept of mean fitness (w̄) and the relative fitness values of the genotypes. The mean fitness is calculated as: $w̄\; =\; p²w₁₁\; +\; 2pqw₁₂\; +\; q²w₂₂$, where p and q are the frequencies of alleles C₁ and C₂, respectively, and w₁₁, w₁₂, and w₂₂ are the relative fitness values of the genotypes.
3. Step 3: Set up the recurrence equations for allele frequencies. The change in allele frequency due to selection can be expressed as: $\Delta p\; =\; p(w̄\; -\; w₁)$ and $\Delta q\; =\; q(w̄\; -\; w₂)$, where w₁ and w₂ are the average fitness contributions of alleles C₁ and C₂, respectively. At equilibrium, Δp = 0 and Δq = 0.
4. Step 4: Solve for equilibrium frequencies. At equilibrium, the allele frequencies stabilize such that the mean fitness (w̄) is maximized. Use the fitness values provided (w₁₁ = 0.30, w₁₂ = 0.60, w₂₂ = 1.0) and substitute them into the equations for w̄ and Δp to find the equilibrium frequencies of C₁ and C₂. This involves solving a system of equations numerically or algebraically.
5. Step 5: Interpret the results. Once the equilibrium frequencies are calculated, interpret the biological significance. The equilibrium frequencies reflect the balance between selection pressure (due to predation) and the genetic makeup of the population. The allele C₂, associated with red flowers, is expected to increase in frequency due to its higher relative fitness.

Key Concepts

Codominance

Codominance is a genetic scenario where two different alleles at a locus are both expressed in the phenotype of a heterozygote. In this case, the alleles C1 and C2 produce distinct flower colors: C1C1 results in yellow, C1C2 in orange, and C2C2 in red. Understanding codominance is crucial for predicting how these alleles will interact in a population under selective pressures.

Natural Selection

Natural selection is the process by which certain traits become more or less common in a population based on their impact on survival and reproduction. In this scenario, the predation of yellow and orange flowers leads to differential survival rates among the flower genotypes, affecting their relative fitness. This concept is essential for understanding how environmental pressures can shape allele frequencies over time.

Hardy-Weinberg Equilibrium

The Hardy-Weinberg equilibrium describes a theoretical state in which allele frequencies in a population remain constant from generation to generation in the absence of evolutionary influences. However, when natural selection occurs, as seen with the predation on certain flower colors, the equilibrium is disrupted, and allele frequencies will change. This concept is vital for calculating the new equilibrium frequencies of alleles C1 and C2 after selection.