A model of quantitative traits under frequency-dependent balancing selection.

We describe a computer model that stimulates a combination of stabilizing and frequency-dependent selection acting on a quantitative character determined by several loci. The results correspond to many features of natural variations at both the phenotypic and genotypic levels. The model is robust, and its results are not strongly dependent either on the nature and shape of the function describing the stabilizing selection, or on the precise form of frequency dependence, except near the extrema. It suggests a mechanism for the maintenance of large amounts of variability, and shows a relation between population size and heterozygosity roughly corresponding to that found in nature. In this respect it is unlike the purely neutral model.