ACCOUNTING FOR BIAS IN ESTIMATES OF THE RATE OF POLYGENIC MUTATION

Experimental data on the rate of response to artificial selection in i nitially inbred lines or the rate of divergence among inbred sublines can be used to estimate the rate of increase in variance of quantitati ve traits from new mutations. So far estimates have been based on the infinitesimal model of many genes with small additive effects which im ply a rate of increase in heritability for Drosophila melanogaster bri stle number traits of about 0.1 % per generation. Such estimates are b iased because mutants tend to have large effects, to have non-additive gene action, and to be deleterious. Here, recent,information on the d istribution of effects of new mutations on Drosophila melanogaster bri stle number and viability is used to infer the direction and magnitude of this bias. The infinitesimal model tends to underestimate the muta tional variance, typically by a factor of about 3, but this factor dep ends on the experimental design. Averages of revised estimates, accoun ting for this bias, of the per generation increment in heritability fr om mutation are 0.36 % and 0.21 % for abdominal and sternopleural bris tle number, respectively, in experiments involving M strains, and 1.4 % and 0.7 % for abdominals and sternopleurals, respectively, in P stra ins.