Some Population Genetic Models Combining Artificial and Natural Selection Pressures

Abstract

The evolutionary behavior of a diploid population characterized by a trait determined at one or two major loci subject to the combined effects of artificial and natural selection pressures is investigated. A number of different genotypic phenotypic associations are set forth, including additive allelic effects and additive loci effects with a' variety of culling programs. Threshold selection schemes as well as culling favoring intermediate phenotypic values are considered. For these formulations results are reported concerning the dynamic progress of the population, a delineation of the numbers and properties of the stable equilibria outcomes, and a discussion of their qualitative and quantitative dependence on the two kinds of selection forces. The level of culling can be used as a control through which natural selection parameters can be estimated. This paper reports results on the consequences of implementing some specific artificial selection programs on populations, taking account of certain natural genetic and ecological forces. We deal with a large diploid population characterized by a trait determined at several loci. To ease the exposition, the discussion will be in terms of two loci with two alleles at each locus, labeled A,a and B,b respectively, involving the usual 10 genotypes. The genotypic phenotypic associations are described in two formulations. The phenotypic value is determined as in [2] (i.e., additive allelic contributions). The culling criterion is directional in favor of the phenotypes P3 and P4, and the viability prescriptions are as follows, where s is the selection coefficient.