Visible and Lethal Mutations in Drosophila

Abstract

Foremost among the questions confronting us in the investigation of the genetic effects of nuclear detonations is that concerning the relative biological effectiveness (RBE) of fast neutrons and X-rays. Contrary to most of the published reports on fast neutrons versus X-rays in producing mutations and chromosome alterations in Drosophila (Catcheside and Lea, 1945; Catsch et al., 1944; Demerec et al., 1942; Dempster, 1941; Eberhardt, 1943; Fano, 1941, 1944; Giles, 1943; Lea, 1947; Thoday and Lea, 1942; TimofeeffRessovsky and Zimmer, 1938, 1939; Zimmer and Timofeeff-Ressovsky, 1938, 1942), we find that fast neutrons are at least twice as effective or have a much higher RBE for all the genetic effects studied. Several genetic criteria have been used to measure the degree of the effect caused by treating the mature male germ cells of Drosophila with X-rays and with fast neutrons both from nuclear test devices and from the cyclotron: the frequencies of (1) recessive visible mutations at specific loci on the third chromosome, (2) dominant visible mutations, both autosomal and sex-linked, (3) dominant Minute effects, and (4) recessive sexlinked lethal mutations. In addition to our own data we shall include some results of other investigators, notably those of Baker and Von Halle (1954) on dominant lethal effects. The most commonly used measure of radiation damage is the rate of sex-linked recessive lethal mutations because of the greater ease and objectivity of scoring as compared to most other types of effects. Recently, the use of dominant lethals has come into favor for testing the effectiveness of radiations (Pontecorvo, 1942; Lea and Catcheside, 1945; Baker and Von Halle, 1953; Luning, 1952). It would be a mistake to restrict our observations on mutation frequencies to lethals, however, since there is evidence that they are not entirely analogous to visible gene mutations. Most of the earlier studies on visible mutations have dealt with sexlinked characters because of the greater ease of detecting them (Timofeeff-