Evolution of Dominance through Incidental Selection

Dominance is a form of phenotypic robustness to mutations. Understanding how such robustness can evolve provides a window on how the relation between genotype and phenotype can change during evolution. Within population genetics, attempts at explaining the evolution of dominance have always run into the problem that selection for dominance is sensitive to the initial frequency of heterozygotes and/or mutation rates. Given such requirements, dominance is unlikely to evolve in most cases. In this article, we present a theoretical model that integrates enzyme kinetics, genetics, and population dynamics to address dominance evolution in metabolic physiology. Given the mechanistic constraints of Michaelis-Menten-type enzyme catalysis, we show that dominance can evolve through a selection regime that is insensitive to the frequency of heterozygotes and/or mutation rates. This is due to the prevalence of alleles that have direct fitness effects in addition to dominance modification effects. Dominance can evolve as an incidental side effect of selection for such dual-effect alleles.