The influence of the temporal distribution of the X-ray dose on the induction of X-chromosomal nondisjunction and X-chromosome loss in oocytes of Drosophila melanogaster

Abstract

The influence of dose fractionation and dose protraction on the induction of X-chromosomal nondisjunction and X-chromosome loss by X-rays in immature oocytes of Drosophila melanogaster has been investigated. In all experiments a dose of 1800 R was used. The dose rate was 850 R/min in the concentrated and fractionated treatments. As compared with the frequency obtained after a concentrated irradiation, the induction of nondisjunction was not influenced by dose fractionation (1-, 3- and 5-h intervals, respectively, between the halved dose). However, dose protraction (10 R/min) reduced the nondisjunction frequency highly significantly, and by a factor of about 1 4 . In the analogous experiments on X-xhromosome loss (“true” losses, because losses resulting from nondisjunction were subtracted), both after dose fractionation and dose protraction the X-loss frequency decreased highly significantly, the reduction being more pronounced after protraction than after fractionation (under the special conditions of our experiments). The results are discussed in connection with the mechanism of radiation-induced nondisjunction and chromosome loss.