In the case of underdominance, it turns out that the positive equilibrium frequency of alleles A and a given by,

is unattainable. This means that unless the initial allele frequencies are these exact equilibrium frequencies,the positive equilibrium frequencies will never be reached. For this reason, we call such a equilibrium unstable.

The stable equilibria are the monomorphic states, (p_eq, q_eq) = (1, 0), in other words all individuals have genotype AA, and, (p_eq, q_eq) = (0, 1), i.e. all individuals have genotype aa. These monomorphic equilibria are said to be locally stable because what happens to the allele frequencies as t → ∞ depends on the initial allele frequencies (p₀ and q₀). In particular, if (p, q) → (p_eq, q_eq) = (0, 1) as t → ∞.

Using this information, what happens to the frequency of allele A as t → ∞ if q₀ = 0.9 and the fitness values for genotypes AA: Aa : aa are 1.8: 1 : 1.2, respectively?

A.

B.

C.

D.