The Influence of X-Rays and Near Infra-Red Rays on Recessive Lethals in Drosophila Melanogaster

The study here reported concerns the effect of supplementary treatment with near infra-red radiation on the frequency with which x-ray-induced recessive lethal mutations are produced in Drosophila melanogaster.Earlier work had shown that when near infra-red rays (X ca.10,000 A) are used prior to x-rays in the treatment of the spermatozoa of D. melanogaster, a marked increase occurs in the frequency of 'detectable chromosomal re- arrangements over that of controls receiving only the dose of x-rays.On the other hand, the percentage of dominant lethals is not significantly higher when near infra-red treatment precedes the x-rays than when x-rays alone are used.'We have now collected additional data which indicate that such supplementary treatment has no significant effect in this species on the frequency of production by x-rays of sex-linked recessive lethals.2Experimental procedures involved the use of the CIB method for de- tection and verification of X-chromosome lethals.Irradiated males were mated with females of the constitution CIB vlec ct6 v g3; Cy/Pm.The maintenance of Pm in the stock, and the selection of F, females carrying this marker, readily permitted the detection of the non-disjunctional XX Y exceptions, because of the suppressing effect of the Y-chromosome on eye-color variegation, and facilitated thereby the diagnosis and scoring of the F2 cultures.Males of the Swedish-b6 stock were used; they were obtained from cultures derived from a single pair of flies that had been tested cytologically to insure freedom from chromosomal aberrations.The males were selected three to five days after their emergence and divided into two groups of approximately equal numbers.One of these groups was exposed to near infra-red radiation (as described by Kaufmann, Hollaender and Gay, 1946)1 for a period of 48 hours either preceding (pretreatment) or following (post-treatment) exposure to x-rays.During this two-day period the group of males that represented the "controls" was kept at a temperature of 180C.Both groups were exposed simultaneously to a 3000-roentgen dose of x-rays in capsules lying -side by side.Following the combined treatment, the males were mated with CIB females and allowed to remain in culture bottles for three days before being discarded.This relatively short mating period was chosen as a standard in order to permit determi- PROC.S~. A. S.