Prolongation of MGE 412 transposition induction after γ-irradiation in an isogenic line of Drosophila melanogaster

The dose dependence of the rate of gamma -induced transpositions and consequent dynamics of the MGE 412 pattern after gamma -irradiation were investigated in isogenic line 49 in generations F-1, F-12, F-140, and F-170. It was shown that the results on dose dependence of transpositions was very similar with the corresponding results of the classic works by Timofeeff-Ressovsky et al. (1935). It is suggested that the transcribed copies of retrotransposon 412 cure gamma -radiation-induced double-strand DNA breaks. The phenomenon of prolongation of MGE transposition induction during early generations after treatment was shown. In this period (F-1-F-12), the maximum transposition rate (lambda similar or equal to 2 x 10(-2) events per MGE copy, per haploid genome, per generation) and the maximum number of heterozygous MGE copies were achieved. In the late generations (F-140-F-170), the reduced induction level (gamma similar to 10(-3)) was established. In the population of effective size N-e = 2000 individuals, this corresponds to the state when lambda much greater than 1/4N(e) i.e., when the transposition flow prevails over the MGE copy loss by genetic drift. These data together with some indirect evidence argue for the hypothesis that the spontaneous transposition rate is proportional to the average number of heterozygous MGE copies per diploid genome.