FREQUENCY OF DELETERIOUS CHROMOSOMES AND ALLELISM BETWEEN LETHAL GENES IN JAPANESE NATURAL POPULATIONS OF <i>DROSOPHILA MELANOGASTER</i>

Abstract

Genetic variabilities in Japanese natural populations of D. melanogaster distributed at Kofu-Katsunuma locality have been analyzed. The frequency of lethal and semilethal chromosomes was 21.5 per cent in coadapted genetic background and 36 per cent in Samarkand isogenic background during the past seven years. The effect of the genetic background on the viability of homozygotes was remarkable for homozygous semilethal and subvital chromosomes. This means that a coadaptive interaction may exist between chromosomes.A clear negative correlation between the frequency of deletelious chromosomes and ‘relative’ viability of quasinormal homozygotes was observed in Drosophila populations including Kofu-Katsunuma.Allelic rates between lethal genes extracted from the natural populations fluctuated during the past several years. The average allelic rate was 3.48 par cent. The low frequency of deleterious genes and high frequency of allelism was assumed to be characteristic for Far East and Russian populations of D. melanogaster.The frequency of elimination (IQ2) caused by deleterious genes in homozygotes was estimated to be 0.0016 in average Kofu-Katsunuma population which was comparatively higher than in other natural populations. On the other hand, the mutation rate (UL+SL) of lethal and semilethal genes on the second chromosome was assumed to be 0.0075, so that the fitness of heterozygotes for deleterious genes should be, on the average, inferior to that of normal heterozygotes and they would be selected out from the natural populations in Japan.