The Genetic Structure of Natural Populations of DROSOPHILA MELANOGASTER. Xvii. a Population Carrying Genetic Variability Explicable by the Classical Hypothesis.

About 400 second chromosomes were extracted from the Aomori population, a northernmost population of D. melanogaster on Honshu in Japan, and the following experimental results were obtained. (1) The frequency of lethal chromosomes was 0.23. (2) The effective size of the population was estimated to be about 3000, from the allelism rate of lethal chromosomes and their frequency. (3) The detrimental and lethal loads for viability were 0.243 and 0.242, respectively, and the D/L ratio became 1.00. (4) The average degree of dominance for mildly deleterious genes was estimated to be 0.178 +/- 0.056. (5) Additive (sigma(2) (A)) and dominance (sigma(2) (D)) variances of viability were estimated to be 0.00276 +/- 0.00090 and 0.00011 +/- 0.00014, respectively. (6) There was no significant difference in environmental variances between homozygotes and heterozygotes. Using these estimates, we discuss the maintenance mechanisms of genetic variability of viability in the population. The mutation-selection balance explained these experimental results.