DIRECTED CHARACTER OF GENETIC CHANGES DUR ING LONG-TERM SELECTION OF DROSOPHILA-MELANOGASTER STRAINS FOR ADAPTIVELY IMPORTANT CHARACTERS

Related fly strains that were selected for differences in reproductive function for about 700 generations were studied. The low-active (LA) strain differs from other related and highly active strains of interes t at a set of characters. Qualitative differences in the spectrum of v iability mutations are retained in strains selected in opposite direct ions. Low-active strains carry a great number of deleterious mutations . Such mutations are rare in the related highly active strains. Moreov er, about 50% of chromosomes in the highly active strains carry superv ital mutations, which increase viability. Recombination analysis showe d the presence of at least several viability mutations in each chromos ome of the strains studied. Unlike highly active strains, the low-acti ve ones are characterized by an extremely high spontaneous mutation ra te. The conservation of genetic heterogeneity observed in long-term se lected strains, as well as the high mutation rate, must be connected w ith regular changes in the spectrum of retrotransposons (MDG1, MDG3) a nd hobo elements characteristic of the strains studied. A special cros sing system that induces a sharp increase in LA induction potential in the H-E system of hybrid dysgenesis was developed.