ANTAGONISTIC PLEIOTROPY, REVERSAL OF DOMINANCE, AND GENETIC-POLYMORPHISM

Conditions for polymorphism at pleiotropic loci with antagonistic effe cts on fitness components are investigated, under the assumptions of a dditivity and multiplicativity of fitness components. We show that the conditions for stable polymorphism are rather restrictive, especially with weak selection. The conditions are also very sensitive to the do minance parameters; in particular, reversal of dominance is often requ ired for stable polymorphism. A review Of biochemical mechanisms of do minance suggests that dominance reversal is not likely to be common. T he conditions for maintaining genetic variation at two antagonistic an d pleiotropic loci are even more restrictive than for the one-locus ca se. When conditions for stable polymorphism by antagonistic pleiotropy are satisfied, substantial dominance variance in one or both fitness components is expected but is seldom observed in experiments. Antagoni stic pleiotropy implies stabilizing selection on the fitness component s separately, which usually tends to reduce genetic variance. We concl ude that, even though trade-offs in fitness components may be common, antagonistic pleiotropy probably plays a limited role in explaining th e persistence of genetic variation in fitness components.