The Response to Artificial Selection Due to Autosomal Genes of Large Effect I. Changes in Gene Frequency at an Additive Locus

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Abstract
In this series of papers, it is proposed to examine the theoretical consequences of the segregation of genes of large effect in populations under artificial selection. The problem or assigning selective values to the genotypes at such a locus is discussed in this paper, and the behaviour in large populations of an additive autosomal gene with 2 alleles is examined in detail. A description is give of the effects of selection for genes of large effect on 3 observable phenomena the ratio of realized to predicted response and its dependence on the intensity of selection imposed: the asymmetry of response to be expected in 2-way selection experiments; changes in the magnitude of the total additive genetic variance. It is concluded that under selection of low intensity, the segregation of a small number of genes of large effect is unlikely to lead to appreciable departure from the predicted rate of response in either the positive or negative directions, or to conspicuous changes in phenotypic variance, over a 5-generation period. Under selection of high intensity on the other hand, one can consider the possibility of such loci contributing up to 5% of the additive genetic variance present in the base population, without leading to dramatic changes in variance under short-term selection. Loci of proportionate effect in the neighbourhood of TO may then give rise to pronounced asymmetry and to conspicuous from predicted rates of response.

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