The number of loci affecting a quantitative trait in Drosophila melanogaster revealed by artificial selection

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Abstract
Individual and within-full-sib family selection for low sternopleural bristle number was carried out for 17 generations, with 6 replicate lines for each selection method. The results can be summarized as follows: the response to selection was exhausted very quickly, the additive variance of the selected lines declined rapidly, the variation in response to selection decreased as selection progressed, genetic differences among replicates at the selection limit were small, individual selection resulted in a higher initial response than within-family selection, but similar limits were achieved with both procedures. Hypothetically, the pattern of response to selection is due to the segregation in the base population of only a few loci with large effects, at intermediate frequencies.