Fractional and complete mutations following irradiation of drosophila spermatids in nitrogen or in oxygen

Abstract

The induction of complete and fractional mutations at the yellow, white, singed and dumpy loci has been studied in Drosophila melanogaster spermatids irradiated with 1000 R of X-rays in O 2 or in N 2. The results show that: ( a) the frequency of fractionals at the y, w and sn loci does not differ significantly from the spontaneous values and this is so, irrespective of the gaseous atmosphere used during the irradiation; ( b) the oxygen enhancement ratio (O.E.R.) for the induction of complete mutations at these loci is 3.1; ( c) at the dp locus the difference between the frequency of fractional mutations in the irradiated series and that in the controls is on the borderline of significance; ( d) at the same locus the O.E.R. for completes is high, being about 5.4. The proportion of dp fractionals among dp mutations appears to decrease from 43.5% after 1000 R in N 2 to 26.2% after the same exposure in O 2. While this observation may be interpreted as being consistent with the predictions of either the lethal-hit hypothesis or the repair hypothesis under certain conditions, the role of other factors that might cause a similar shift in the proportion must be taken into consideration. The data on the induction of fractional and complete mutations at the dp locus, considered in conjunction with the data of other loci from this study as well as those published by other investigators, suggest that the fractional and complete mutations detected after irradiation may have independent origins. With the exception of the dp locus, the evidence for the induction by radiation of fractional mutations at other loci investigated is not convincing. The high O.E.R. of 5.4 estimated for the induction of dp completes is thought to result from the induction kinetics for these mutations, which, even at the exposure of 1000 R in O 2 may have a sizeable two-hit component.