QTL analysis reveals variation in <i>bruno</i> mediates natural tolerance to P element–induced gonadal atrophy.

Natural variation in resistance to hybrid dysgenesis was identified using a large number of RILs from the DSPR. A key feature of the DSPR is that it was constructed from strains that lack P element insertions and, hence, also lack P element piRNAs. Multiple females from each RIL were crossed to males of a P strain with a strong capacity to induce dysgenesis. Variation in tolerance to P element–induced atrophy was revealed by performing crosses at a mildly permissive temperature. This experiment revealed a tremendous amount of variation: some strains exhibit no gonadal atrophy, while others exhibit complete gonadal atrophy. Using this variation in a QTL analysis, segregating variation at the bruno gene was found to be an important determinant of tolerance to P element–induced sterility in the DSPR. DSPR, Drosophila Synthetic Population Resource; QTL, quantitative trait locus; RIL, recombinant inbred line.