CYTOGENETIC STUDIES OF X-RAY AND INGESTED P32 INDUCED SEX-LINKED RECESSIVE LETHALS IN DROSOPHILA MELANOGASTER

Abstract

Male flies were either irradiated with 1000 r or fed a sugar solution containing Pa/sup 32/. The latter flies attained an average activity of 75 C. The males were immediately mated with unirradiated females according to the brood pattern technique. Chromosomal aberrations (deletions, translocations, and inversions) were recovered following treatment with either mutagen. The distribution of point mutation lethals induced on the X chromosome by P/sup 32/ was identical to the one found after x-ray treatment. The highest frequency of sex-linked recessive lethals in the P/sup 32/ series was found on days 7 and 8, as compared with day 5 for the x-ray series. The sterile period in the x-ray series following the exhaustive mating system used may be attributed partially to dominant lethals, lack of functional sperm, and to meiotic or mitotic inhibition due to irradiation. P/sup 32/ incorporated into the DNA of mature sperm was recovered 7 to 8 days after a single meal, under conditions of excessive mating, which coincides with maximum genetic effect. Thus the results favor the concept that the period of maximum DNA synthesis corresponds to the period of maximum lethal induction and/or of chromosome breakage. (H.H.D.)