THE SELECTIVE VALUE OF ALLELES UNDERLYING POLYGENIC TRAITS

Michael Lynch 1

1 Department of Ecology, Ethology, and Evolution, Shelford Vivarium, University of Illinois, Champaign, Illinois 61820

To define the genetic and ecological circumstances that are conductive to evolution via genetic drift at the allelic level, the selection coefficient for a constituent allele of arbitrary effect is derived for a polygenic character exposed to stabilizing selection. Under virtually all possible conditions, alleles within the class for which the absolute value of the average effect is <10-2 phenotypic standard deviations are neutral with respect to each other. In addition, when the mean phenotype is at the optimum and the genetic variance is in selection-drift-mutation equilibrium, a considerable amount of neutral evolution is expected in the class of alleles with intermediate effects on the phenotype. These results help clarify how molecular evolution via genetic drift may occur at a locus despite intense selection and provide a potential mechanistic explanation for the neutral theory of molecular evolution.

Submitted on May 18, 1984
Accepted on August 17, 1984