Back mutation in Drosophila melanogaster. II. Data on additional yellow and white mutants.

HE previously reported X-ray-induced back mutations of the recessive sexT inked mutants yellow-2 (yz), scute (sc) and white-apricot (w”) (GREEN 1961a) supplemented and extended existing data for Drosophila melanogaster on induced back mutations of the forked mutants f’ and f”” and white-ivory (wz) (MULLER and OSTER 1957; GREEN 1959a; LEFEVRE and GREEN 1959; LEWIS 1959) and leave little doubt that X rays can induce back mutations. An appraisal of all of these data suggests the following general conclusions. First, those mutants which spontaneously back mutate are the more prone to induced back mutation. Second, the frequency of X-ray-induced back mutation is a characteristic of the particular mutant rather than of the locus. Third, the qualitative nature of the induced back mutant, i.e., whether full or partial, is also a property of the individual mutant. Fourth, the back mutation pattern of partial back mutants appears not to differ from that of the mutants from which they arose. Fifth, premeiotic cells are more back mutation sensitive than are meiotic cells. The data of TIMOF~EFF-RESSOVSKY (1933, 1939) conflict with the fourth generalization. He reported that whereas back mutation to wild type could be induced after irradiating white-eosin (we) males, comparable back mutants could not be obtained from w from which we arose. Furthermore, his recovery of a substantial number of back mutations after irradiating males is contrary to the fifth generalization. Therefore, back mutation studies of we and equivalent partial back mutations of w were undertaken. Additional yellow body color ( y ) mutants and the mutant acheate (ac) for which GOLDAT (1936) had recovered a single induced back mutant were simultaneously studied.