An &&adaptive dynamics'' modelling approach to the evolution of dominance-recessivity is presented. In this approach, "tness derives from an explicit ecological 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 selection model. Evolutionary freedom is allowed at a single locus. The evolutionary analysis considers directed random walks on trait space, generated by repeated invasions of mutants.
The phenotype of an individual is determined by allelic parameters. Mutations can have two e!ects: they either a!ect the a$nity of the promoter sequence for transcription factors, or they a!ect the gene product. The dominance interaction between alleles derives from their promoter a$nities.
Additive genetics is evolutionarily unstable when selection and evolution maintain two alleles in the population. In such a situation, dominance interactions can become stationary and close to additive genetics or they continue to evolve at a very slow pace towards dominance-recessivity. The probability that a speci"c dominance interaction will evolve depends on the relative mutation rate of promoter compared to gene product and the distribution of mutational e!ect sizes. Either allele in the dimorphism can become dominant, and dominance-recessivity is always most likely to evolve. Evolution then approaches a population state where every phenotype has 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 favours a population of two alleles under the same conditions as for a regulated locus. In the case of a housekeeping gene, however, the evolutionary dynamical system approaches a population state where the heterozygote and only one homozygote phenotype are equivalent to the optimum phenotypes in the two patches.