THE RELATIONSHIP BETWEEN RADIATION EXPOSURE AND MUTATION RATE AT THE <i>DUMPY</i> LOCUS IN <i>DROSOPHILA</i>

The prequency pattern of the dumpy mutations induced by X-rays in different stages of spermatogenesis of Drosophila.

“…Such differential response patterns between these two classes are not unexpected in view of our earlier findings (Inagaki et al 1974) that the dose-response curve of the of and lv exceptions tends to increase faster than linearly whereas that of the o and v ones exhibits plateau at higher dose levels. Recently, Miyamoto (personal communication)…”

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The dumpy locus (dp) located on the chromosome 2 at map position 13.0 is among the loci intensively studied in Dyosophila.Its usefulness and suitability for mutational studies derive from the findings that (i) it is a complex locus (or a closely linked group of distinct genes) with no less than 7 mutational sites Grace 1970), events at which are phenotypically detectable in certain combinations; (ii) the locus is much more sensitive than others to radiation as well as chemical mutagens Carlson and Oster 1962;Oster 1963;Jenkins 1967;Corwin 1968) and (iii) the induced events at this locus involve presumed point mutations as well as those associated with chromosome breakage, the latter resulting in extreme phenotype Carlson and Oster 1962).In an attempt to shed more light on the nature of radiation-induced dumpy mutations, a comparison was recently made by Inagaki et al (1974) for the dose-frequency patterns between the different kinds of dumpy exceptions induced by X-rays in mature sperm. The experimental data revealed that (a) the yield of dumpy exceptions of the o and v types increases with exposure up to 3,000 R beyond which there is no further increase; (b) the frequency of the of and the lv exceptions tends to increase faster than linearly with no evidence for a decrease at 4,500 R; (c) the exposure-frequency relationship for the ov and olv exceptions does not depart from linearity; (d) the over-all frequencies of o, v, of and lv at the three exposure levels (1,500, 3,000 and 4,500 R) are also consistent with linear increase with exposures and (e) the frequency of fractional dumpy mutants appears to remain approximately the same irrespective of the exposure.

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“…In an attempt to shed more light on the nature of radiation-induced dumpy mutations, a comparison was recently made by Inagaki et al (1974) for the dose-frequency patterns between the different kinds of dumpy exceptions induced by X-rays in mature sperm. The experimental data revealed that (a) the yield of dumpy exceptions of the o and v types increases with exposure up to 3,000 R beyond which there is no further increase; (b) the frequency of the of and the lv exceptions tends to increase faster than linearly with no evidence for a decrease at 4,500 R; (c) the exposure-frequency relationship for the ov and olv exceptions does not depart from linearity; (d) the over-all frequencies of o, v, of and lv at the three exposure levels (1,500, 3,000 and 4,500 R) are also consistent with linear increase with exposures and (e) the frequency of fractional dumpy mutants appears to remain approximately the same irrespective of the exposure.…”

The brood pattern of X-ray-induced dumpy mutations in males of a wild type strain of Drosophila melanogaster.

“…Using f-96 strain, however, Inagaki et al (1977b) have revealed that a striking difference exists in the brood-mutation patterns between the exceptions of the olv, ov, of and lv types and those of o and v types instead of the difference between the olv and ov typee and the ol, lv, o and v types noted in the present study. In this strain, such differential response patterns between the of and lv exceptions and the o and v exceptions have been found also in the dose effect relationships (Inagaki et al 1974) ; the yield of the of and lv exceptions tends to increase faster than linearly whereas that of o and v ones show plateau at higher exposure levels. Probably, strain specific differences due to the differences in the genetic background (e.g., the existence of inversions) may be responsible for these two kinds of phenomena.…”

“…The results show that the yield of the olv and ov exceptions varies in the different germ cell stages, while this is not so for the ol, lv, o and v exceptions. This brood-mutation pattern for the of and lv exceptions is quite different from that elucidated in scsl B In49 sc8/BS Y sc8 males.On the nature of X-ray-induced dumpy mutations in Drosophila melanogaster, it has been already reported that these mutations arise from chromosome breakage events and gene mutations (Carlson and Southin 1962) In recent years, attempts to shed more light on the nature of the different kinds of dumpy mutations (o, v, ol, lv, ov and olv types, see Carlson and Oster 1962;Lindsley and Grell 1968) induced by X-rays have been made by several workers (Inagaki et al 1974;Inagaki et al 1977b;Miyamoto 1978;Fujikawa and Inagaki 1979). Using scSi B 1n49 sc8/BS Y sc8 (f-96) strain, Inagaki et al (1977b) have revealed that the yield of the olv, ov, of and lv exceptions is affected to a considerable extent by the difference in the different cell stages of spermatogenesis, while that of the o and v exceptions is affected only a little, indicating that a striking difference exists in the brood-mutation pattern between the of and lv exceptions and the o and v exceptions.…”