THE PREQUENCY PATTERN OF THE DUMPY MUTATIONS INDUCED BY X-RAYS IN DIFFERENT STAGES OF SPERMATOGENESIS OF DROSOPHILA

抄録

The frequency patterns for the different kinds of dumpy mutations induced by X-rays in successive stages of spermatogenesis were studied by making two-day brood changes with 3 females per male per brood. With this mating procedure, mature sperms are probably sampled in brood A, late spermatids in brood B, early spermatids and presumably late spermatocytes in brood C, early spermatocytes in brood D.
The experimental results obtained indicate that (i) the over-all frequencies of recovered complete dumpy mutations are relatively similar in broods A and B, begin to increase gradually in brood C, reach its highest level in brood D and decline sharply in brood E; (ii) the frequency patterns for the (ol, lv) and (ov, olv) exceptions over the five sampling broods are practically similar to that observed in the total dumpy mutations; (iii) no such differences in brood-mutation pattern are found, however, with respect to the yield of the (o, v) types; (iv) the over-all frequencies of recovered fractional dumpy mutations appear to be relatively steady from stage to stage, although the majority of the fractionals are of the o and v types.
These findings indicate that the different kinds of dumpy exceptions may be differentially affected under different germ cell stages of maturity. Probably, this might represent a difference between point mutations and breakage events.