Departures from assumptions of additive, symmetrical, normal and non- pleiotropic distributions of effects of mutations affecting quantitative traits are discussed with respect to theoretical models predicting long-term response to directional selection, divergence between populations and maintenance of quantitative genetic variation within populations. That these assumptions may be violated is inferred from observations of long-term selection response, studies of the effects of spontaneous and induced mutations on quantitative traits, and mapping quantitative trait loci. The results of an experiment are presented in which the effects of new, stable P element insertions, in an inbred host background originally free of P elements, were determined on viability and two bristle traits in Drosophila. The distributions of homozygous effects of the new insertions on the bristle traits are skewed and highly leptokurtotic. The effects are mostly recessive, and show pleiotropy in that both bristle traits are sometimes affected and viability is reduced.

T. FC Mackay

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume XIII. Plenary lectures, molecular genetics and mapping, selection, prediction and estimation., , 219–227, 1990
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