The Persistence of Some Recessive Lethal Genes in Natural Populations of Drosophila melanogaster. II

Abstract

The frequency of second chromosomes bearing deleterious genes in the same natural populations of D. melanogaster was repeatedly estimated during the past three years. The incidence of lethal genes, about fifteen per sent, was maintained nearly without fluctuation. Three and two lethal genes of the twenty-four lethal genes isolated in 1960 seemed to have been retained at least for one year and two years respectively in the same natural population. The selection coefficients of their heterozygotes were estimated by the Cy-Pm technique, and the average viability was found to be about three per cent lower than that of normal heterozygotes. The selection coefficients of several chromosomes bearing allelic lethal genes were not always concurrent; these variations in viabilities of their heterozygotes are probably due to the difference in the genetic background.