The evolutionary ecology of dominance-recessivity

An "adaptive dynamics" modelling approach to the evolution of dominance-rec essivity is presented. In this approach, fitness derives from an explicit e cological scenario, and both evolutionary attractivity and invasibility of resident populations are examined. The ecology consists of a within-individual part representing a locus with regulated activity and a between-individual part that is a two-patch soft s election model. Evolutionary freedom is allowed at a single locus. The evol utionary analysis considers directed random walks on trait space, generated by repeated invasions of mutants. The phenotype of an individual is determined by allelic parameters. Mutatio ns can have two effects: they either affect the affinity of the promoter se quence for transcription factors, or they affect the gene product. The domi nance interaction between alleles derives from their promoter affinities. Additive genetics is evolutionarily unstable when selection and evolution m aintain two alleles in the population. In such a situation, dominance inter actions can become stationary and close to additive genetics or they contin ue to evolve at a very slow pace towards dominance-recessivity. The probabi lity that a specific dominance interaction will evolve depends on the relat ive mutation rate of promoter compared to gene product and the distribution of mutational effect sizes. Either allele in the dimorphism can become dom inant, and dominance-recessivity is always most likely to evolve. Evolution then approaches a population state where every phenotype has maximum viabi lity in one of the two patches. When the within-individual part is replaced by a housekeeping locus that co des for a metabolic enzyme, evolution favours a population of two alleles u nder the same conditions as for a regulated locus. In the case of a houseke eping gene, however, the evolutionary dynamical system approaches a populat ion state where the heterozygote and only one homozygote phenotype are equi valent to the optimum phenotypes in the two patches. (C) 1999 Academic Pres s.