[Change in the distribution of transposable elements in isogenic strain--cause or consequence in Drosophila...

The distribution patterns pf hobo transposon and Dm412 retrotransposon hybridization sites on the salivary gland polytene chromosomes from the larvae of Drosophila melanogaster isogenic strain 51, used for analyzing the effect of transposable element (TE) transposition on the selection for quantitative traits, were studied, It was demonstrated that at least half Dm412 hybridization sites were retained 15 years after isogenization; the frequency of Dm412 transposition varied from 2.0 x 10(-4) to 8.8 x 10(-5) depending on whether the appearance of the same hybridization sites in some individuals were regarded as independent events or as a manifestation of the sample heterogeneity. The distribution patterns of hobo hybridization sites in two isofemale strains derived from isogenic strain 51 differed more noticeably: the number of hobo sites in one of the derivative strains was threefold smaller than in another and only a fraction of the sites was common. Within each derivative strain, the TE distribution was uniform, suggesting that inbreeding had no effect on the Dm412 activity in this strain. The rates of change in the distribution patterns of various TEs in strain 51 corresponded to their spontaneous transposition rates. As isogenic strain accumulates the polymorphism in TE distribution without selection, the TEs are more likely to be the markers of selection events than their inducers. Thus, when studying the effects of various environmental factors on TE transposition even in isogenic strains, it is necessary to perform rounds of close inbreeding to reduce the potential polymorphism.