The Evolutionary Ecology of Dominance-Recessivity

An "adaptive dynamics" modeling approach to the evolution of dominance-recessivity is presented. In this approach fitness derives from an explicit ecological scenario. The ecology consists of a within-individual part presenting a locus with regulated activity, and a between-individual part that is a two-patch soft selection model. Evolutionary freedom is allowed at a single locus. The evolutionary analysis considers directed random walks on trait space, generated by invasions of mutants. The phenotype of an individual is determined by allelic parameters. Mutations can have two effects: they either affect the affinity of the promoter sequence for transcription factors, or they affect the gene product. The dominance interaction between alleles derives from their promoter affinities. I show by means of an example that additive genetics is evolutionarily unstable when selection and evolution maintain two alleles in the population. In such a situation, dominance interactions can become stationary close to additive genetics or they continue to evolve at a very slow pace towards dominance-recessivity. The probability that a specific dominance interaction will evolve depends on the relative mutation rate of promoter compared to gene product and the distribution of mutational effect sizes. Either of both alleles in the dimorphism can become dominant and dominance-recessivity is always most likely to evolve. Evolution then approaches a population state where every phenotype in the population has a maximum viability in one of the two patches. When the within-individual part is replaced by a housekeeping locus that codes for a metabolic enzyme, evolution favors a population of two alleles on the same conditions as for a regulated locus. In the case of housekeeping gene however, the evolutionary dynamics is attracted towards a population state where the heterozygote phenotype equal the optimum phenotypes in the two patches