抄録
Drosophila melanogaster strains homozygous for X chromosomes sampled from natural populations responded to upward and downward selection for glucose-6-phosphate dehydrogenase activity. Second and third chromosomes sampled from the homozygous strains showing a high enzyme activity as a result of selection have no stimulative effect on the enzyme activity. Flies which were made homozygous for X, second and third chromosomes sampled from "high-activity" strains also responded to selection. Since the fourth chromosome constitutes only a minor fraction of D, melanogaster genome, these findings suggest the presence of an extrachromosomal modifier which is responsible for regulation of the enzyme activity. Implication of these findings in adaptive evolution is discussed.
