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Evolution and Selection of Quantitative Traits$
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Bruce Walsh and Michael Lynch

Print publication date: 2018

Print ISBN-13: 9780198830870

Published to Oxford Scholarship Online: September 2018

DOI: 10.1093/oso/9780198830870.001.0001

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Short-term Changes in the Variance: 1. Changes in the Additive Variance

Short-term Changes in the Variance: 1. Changes in the Additive Variance

(p.549) 16 Short-term Changes in the Variance: 1. Changes in the Additive Variance
Evolution and Selection of Quantitative Traits

Bruce Walsh

Michael Lynch

Oxford University Press

Selection changes the additive-genetic variance (and hence the response in the mean) by both changing allele frequencies and by generating correlations among alleles at different loci (linkage disequilibrium). Such selection-induced correlations can be generated even between unlinked loci, and (generally) are negative, such that alleles increasing trait values tend to become increasingly negative correlated under direction or stabilizing selection, and positively correlated under disruptive selection. Such changes in the additive-genetic variance from disequilibrium is called the Bulmer effects. For a large number of loci, the amount of change can be predicted from the Bulmer equation, the analog of the breeder's equation, but now for the change in the variance. Upon cessation of selection, any disequilibrium decays away, and the variances revert back to their additive-genic variances (the additive variance in the absence of disequilibrium). Assortative mating also generates such disequilibrium.

Keywords:   additive-genic variance, additive-genetic variance, assortative mating, Bulmer effect, Bulmer equation, disruptive selection, drift, inbreeding, infinitesimal model, linkage disequilibrium, Mendelian sampling variance, normalizing selection, segregation variance, stabilizing selection, truncation selection

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