The Effects of Two Stage Selection Based on Performance and Progeny Testing on the Genetic Gains

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  • 能力検定および後代検定による2段階選抜の遺伝的改良量に及ぼす影響
  • ノウリョク ケンテイ オヨビ コウダイ ケンテイ ニ ヨル 2ダンカイ センバ

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Abstract

The effects of two stage selection on genetic gains of two traits each independently subjected to selection were examined over 10 generations. Unselected population size at each generation was 1, 000, in which sex was specified with the probability of 0.5. Selection at stage 1 was based on phenotypic value of trait 1 with a selected fraction: 10% for males and 40% for females. At stage 2, half of the males were selected based on the progeny mean of trait 2. Total capacity of progeny testing was limited to 300. The traits were controlled additively by 14 loci each with two alleles. Gene frequency in the base population was arbitrarily set at 0.5 at each locus. Assumed initial heritabilities of trait 1 and trait 2 (h210 and h220) were 0.6, 0.4, or 0.2, and genetic correlation (rgo) was 0.16, 0.0 or -0.16, which was generated by regulating the number and the kinds of pleiotropic loci affecting the traits. All combinations of three heritabilities and three genetic correlations were simulated. The additive genetic variances and heritabilities decreased rapidly at h210=0.6 and h220=0.2, while the decline in covariances and genetic correlations was considerable in the reverse heritability combination. There were no remarkable effects of two stage selection on the cumulative genetic gains of trait 1 (ΔCG1) over a short term at all genetic parameter combinations, although when h210 and rga were lower, ΔCG1 over a long term were slightly less than those by performance testing selection alone. The cumulative genetic gains of trait 2 (ΔCG2) differed according to the parameter combinations. ΔCG2 were considerably less than those attained by progeny testing selection alone, except in the case of h220=0.2 and rgo=0.16, in which larger ΔCG2 relative to the control were observed owing to favorable correlated responses from first stage selection. The decline of ΔCG2 became more clear with higher h210 and lower rgo: for example, negative ΔCG2 were found when h210=0.6 or O.4 and rgo=-0.16.

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