Evolution, Selection against one of the homozygotes

Suppose that one homozygous genotype, say A2A2, has lower fitness than the other two genotypes, A1A1 and A1A2. (This is the situation in many human diseases, such as phenylketonuria [PKU] and sickle-cell anemia. The heterozygotes and the homozygotes for the normal allele have equal fitness, higher than that of the homozygotes for the deleterious allele.) Call the fitness of these