Differential hypersensitivities of Drosophila melanogaster strains with mei-9, mei-41 and mei-9 mei-41 alleles to somatic chromosome mutations after larval X-irradiation

Abstract

The effects of X-ray-sensitive single mei-9 and mei-41 and double mei-9 mei-41 mutations in Drosophila melanogaster on the induction of somatic chromosome mutations by X-rays were examined. Stocks heterozygous for the recessive cell marker mwh (multiple wing hairs) were used. The frequencies and sizes of mwh clones in the wings of adults after X-irradiation were examined. After X-irradiation of third instar larvae of the repair-proficient strain and the mei-9, mei-41 and mei-9 mei-41 mutants at 100 rad, the frequency per wing of large mwh clones was 0.15, 0.25, 0.89 and 1.87, respectively. The 50% lethal dose (LD 50) after X-irradiation of third instar larvae of these strains was 3.5, 2.2, 1.3 and 0.8 krad, respectively. Thus, in terms of either mutation rate at 100 rad or 1/LD 50, the product of the sensitivity to X-irradiation of the repair-proficient strain and that of double mutant mei-9 mei-41 was nearly equal to the product of the sensitivity of mutant mei-9 and that of mutant mei-41. Based on a theoretical model, which can explain this empirical relationship, it is proposed that the X-ray-induced lesions responsible for induction of chromosome mutations or lethality are repaired by two independent pathways, one dependent on the gene mei-9 + and the other on the gene mei-41 +.