The Maintenance of Single-Locus Polymorphism. II. The Evolution of Fitnesses and Allele Frequencies

Abstract

The results of this study demonstrate that moderately polymorphic, uneven equilibria may result from a simple evolutionary process, namely, the invasion of mutant alleles, one at a time, into an extant population of alleles. We have shown that the very small region of the viability parameter space affording stable, feasible polymorphism is easily reached. A remarkable feature of this process is the modification of fitness distributions accomplished by the interaction of simple recurrent mutation and selection, a result that strongly underscores Ginzburg's point that allele frequencies and fitnesses coevolve. Though a substantial fraction of these polymorphic stable equilibria involved total overdominance, the evolution of equilibria in which at least one pair of alleles was not overdominant reminds us that the results of studies of two alleles may be somewhat misleading. The number of alleles maintained here provides only some help in explaining the variation shown in certain electrophoretic data: recurre...