The Effect of Pretreatment with Infra-Red Radiation on the X-ray Induced Sex-Linked Recessive Lethal and Visible Mutation Rate in Drosophila Melanogaster

Abstract

Males from a strain of Oregon - R, inbred for 70 generations, were selected between 2 and 7 days after eclosion and allowed to equilibrate to 15[degree]C before the vials containing them were immersed in a water bath averaging 8[degree]C during infra-red treatment. The infra-red source was a General Electric 250-watt heat lamp, about 13 cm. from the treated flies. Control flies were also immersed and protected from radiation by a black rubber covering. Both control and treated flies were removed from the water bath and X-rayed simultaneously, using a G. E. industrial machine operated at 80 kv. and 10 ma. The Muller -5 stock was used to test for induced mutations and any vial in which 3 or more wild males could be seen simultaneously in a field of up to 30 flies was classed as non-mutant. Visible and lethal mutants were retested, and crossover tests were made of a selected group of lethals, using the y ct6 ras2 f stock. It was found that cold shocks alone or in combn. with 4 hrs. of infra-red treatments did not increase the frequency of sex-linked recessive lethals or visibles, and that pretreatment with 4 hrs. of infra-red did not significantly increase the no. of X-ray induced sex-linked lethal and visible mutations, using X-ray dosages of 1000, 1800 and 2500 r units and Chi-square tests for significance. In the crossing-over studies to test whether the infra-red effect might be obscured by the presence of more than one lethal on the X-chromosome, only one stock out of 40 tested showed the presence of more than one lethal. In the light of these findings and of theoretical considerations it is concluded that recessive lethal and visible mutations do not result from chromosome breakage.