Figure 2.

Illustration of how unequal dominance between the sexes could arise at a sexually-antagonistic autosomal locus. The optimum level of gene product activity is higher in males than in females, and the alleles have additive, sex-independent effects on gene product activity. As a consequence of the concavity of the fitness functions in the vicinity of the optima, whichever allele is beneficial (deleterious) in a given sex is partly dominant (recessive) in that sex. This situation is particularly favorable to the maintenance of polymorphism, because it creates heterozygote superiority when fitnesses are averaged across the sexes.