The evolution of dominance

The evolution of dominance has been subject to intensive debate since Fishe r first argued that modifiers would be selected for if they made wild-type alleles more dominant over mutant alleles. An alternative explanation, put forward by Wright, is that the commonly observed dominance of wildtype alle les is simply a physiological consequence of metabolic pathways. Wright's e xplanation has gained support over the years, largely ending the debate ove r the general recessivity of deleterious mutations. Nevertheless there is r eason to believe that dominance relationships have been moulded by natural selection to some extent. First, the metabolic pathways are themselves prod ucts of evolutionary processes that may have led them to be more stable to perturbations, including mutations. Secondly, theoretical models and empiri cal experiments suggest that substantial selection for dominance modifiers exists during the spread of adaptive alleles or when a polymorphism is main tained either by overdominant selection or by migration-selection balance.