THE PRODUCTION OF MUTATIONS IN DROSOPHILA MELANOGASTER BY THE FAST NEUTRON RADIATION OF AN ATOMIC EXPLOSION

Abstract

Males from an Oregon-R strain which had been inbred for 100 generations, then mass cultured for 10 genera-tions, were exposed to fast neutrons of an atomic explosion. Estimated dosages in REP were given by dosimeters included with the flies, which were shielded from other radiations and effects of the explosion. Within a week after exposure the males were mated individually to Muller-5 females for sex-linked lethal tests and to "res" females for tests of 4 groups of visible mutations: "res"-like, Minute, other bilateral mutants, and unilateral mutants. The sex-linked lethals were tested for crossing over with y ct6 ras2 f. Comparisons were made with the results of soft X-ray tests (120 KV, 10 ma, 200 r per min.) made during the 10 generations of mass culturing. For sex-linked lethal mutation rates 760 REP of fast neutrons were comparable to 2500 r of soft X-rays. In analyzing the lethals in crossing over tests, a lethal chromosome showing either allelism to one of the marker genes in the F1 or abnormal crossing over in both males and females of the F2 "was classed as a complex mutation. For 3 dosages of fast neutrons there were, on the avg., 42.4% complex mutations, most of which showed marked reduction in crossing-over. There was an indication that fast neutrons caused breaks in both the euchroma-tic and heterochromatic regions. The fast neutron series had approx. three times as many complex lethals as the X-ray series and approx. eight times as many as a series involving a naturally occurring mutator. 1400 REP of fast neutrons were approxi-mately equivalent to 2500 r of X-rays in producing simple lethals, and 315 REP equalled 2500 r in producing complex lethals. Fast neutrons were also more effective in producing autosomal visible mutations, with 760 REP equivalent to 3000 r. However, the relative frequencies of the different types of visible mutations were the same for fast neutrons and X-rays except for the class called "other bilaterals" which included chiefly dominant visible mutations and was relatively more frequent in the fast neutron series. Dosage curves in the fast neutron series gave linear relationships for simple and complex lethals, but possibly a non-linear relationship for visible mutations. The gross chromosome damage associated with lethals in the fast neutron series suggested that a single hit was able to produce two or more chromosomal breaks.