Genetic Drift and the Response to Selection in Simulated Populations: the Simulation Model and Gene and Genotype Responses

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Abstract
The effects of population size, selection intensity, mating system, and selection method were studied in a 24 factorial simulation experiment for a quantitative trait undergoing selection for 10 generations and a correlated, unselected trait. Each of two traits was influenced by 60 loci, 30 being in common. Results are presented on selected and unselected gene groups of 30 loci each for gene fixation, gene frequencies, genotypic arrays, and inbreeding for up to 50 replications of each of the 16 factor combinations. The first two factors, population size and selection intensity, were achieved by male:female mating array combinations of 8:8, 5:20, 16:16, and 10:40 with mean inbreeding coefficients for unselected loci of .306, .284, .171 and .152, respectively, after 10 generations. Avoiding sib matings compared to random mating reduced average inbreeding to .028, while restricting selection to within family resulted in an average inbreeding of .191 after 10 generations as compared with .265 for mass selection. Population size interacted with mating system in that avoiding sib matings compared to random mating reduced inbreeding by .040 in small lines, but only .014 in large lines. Within-family selection compared to mass selection reduced inbreeding by .095 in small lines but only .053 in large lines. Within-family selection was more effective in reducing inbreeding in high selection intensity lines than in low. In general, restrictions on selection and mating were more effective in reducing inbreeding as population size decreased. Copyright © 1977. American Society of Animal Science . Copyright 1977 by American Society of Animal Science.

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