Dominant Lethal Mutation and X-Chromosome Elimination after X-Irradiation of Female Drosophila melanogaster

Abstract

The experiments to be described extend earlier studies (1-6) which indicated a decline in the frequency of dominant lethal and sex-linked recessive lethal mutations and in the rate of X-chromosome eliminations found in successive batches of eggs laid subsequent to treatment of female Drosophila melanogaster with ionizing radiations. It is also known that the rate of X-ray-induced deletions and detachments of attached X-chromosomes declines in successive batches of eggs (7-12). Successive batches of eggs represent cells which were at increasingly early stages of o6genesis at thetime of treatment. The question immediately arose as to whether these lowered mutation rates indicate that the mutation process actually occurs at a lower frequency in less mature cells because of differences in radiosensitivity between these and more mature nuclei, or that the lowered rates were due to selection during o6genesis against mutant-bearing cells. It was hoped that a more extensive study of the frequency of dominant lethals and X-chromosome losses found in eggs laid at successive daily intervals after X-ray treatment of female flies might shed some light on this problem.