Overdominance maintaining polymorphism

One of the classic ways to maintain genetic variation with a population is "overdominance," in short, a state where heterozygotes exhibit greater fitness than the homozygote genotypes. Imagine for example a locus, A, with two alleles, A1 & A2. Now, assume the fitness is distributed like so across the genotypes: A1A1 = 0.75 A1A2 = 1.00 A2A2 = 0.75 In a random mating population the equilibrium genotypes given particular allele frequencies are described by the Hardy-Weinberg Equilibrium like so: p^2 + 2pq + q^2 In a diallelic scenario q is by definition 1 - p, resulting in some algebraic simplification (i.e., the above equation is equivalent to p^2 + 2p{1 - p} + {1 - p}^2). We can imagine that A1 is equivalent to p, while A2 is equivalent to q. From the fitness values above we then know that the fitness of the genotypes are: p^2 = 0.75 2pq ...