THE GENETIC LOAD IN THE SECOND CHROMOSOMES OF SOME POPULATIONS OF DROSOPHILA MELANOGASTER IN EGYPT

Abstract

INCE the pioneering work of CHETVERIKOV (1927), species of the genus Drosophila, and particularly Drosophila melanogaster, have been favorite materials for studies on the genetic loads which populations of sexually reproducing species carry (DOBZHANSKY 1951 and 1955 for reviews). Drosophila melanogaster has been used for many studies on the genetics of irradiated and nonirradiated experimental populations (WALLACE 1956 and other works). Nevertheless, much remains to be learned about the behavior of the genetic loads in this species. For one thing, the populations of different countries often differ in that some of them carry more concealed recessive lethal and semilethal genes in their chromosomes than is the case with populations of other countries. This difference probably depends on the environmental conditions in which the populations live, but the nature of the relations are as yet obscure. Moreover, in contrast to some other species (e.g., D. pseudoobscura, D. persimilis, and D. prosaltans, see DOBZHANSKY and SPASSKY 1954), data seem to be wholly lacking on the frequency of recessive subvital variants in wild populations of D. melanogaster. The experiments described in the present article were made for the purpose of filling these gaps.