Effects of inbreeding on the response to selection in a simulated population

Abstract

Simulation experiments were performed to clarify the effect of cyclical full-sib mating on the response to selection for a low-heritability character (h2=0.075 o 0.250) without male phenotypes. There were 32 two-allelic loci affecting the trait, partial dominance over the unfavourable allele at each locus. but no epistasis. In the initial population linkage equilibrium and Hardy-Weinberg genotype frequencies with a gene frequency 0.5 at each locus were generated. The population size was 1500, and in each of the 30 generations 50♂+ 50♀ or 100♂+ 100♀ were selected. In the inbreeding periods (3 generations) selection between full-sib families was employed, whereas in other periods (3 or 6 generations) there was combined selection. For the selected number 50♂+ 50♀ there was no short-term advantage to progress from inbreeding and a loss of 3–5% in the cumulative response relative to the response with avoidance of full-sib mating. The variation of the final response was larger for selection with inbreeding than for that without inbreeding. For the selected number 100♂+ 100 ♀ there was some short-term advantage from inbreeding and an extra gain of 4–8% in the final response when h2 was 0.075, but only a marginal advantage when h2 was 0.25. The variation of response for selection with inbreeding was about the same as for that without inbreeding. It was concluded that the appearance of genetic defects and the decline in fertility might render the selection with inbreeding an unattractive proposal.