The Transmission of Fragmented Chromosomes in Drosophila melanogaster

We investigated the fate of dicentric chromosomes in the mitotic divisions of Drosophila melanogaster. We constructed chromosomes that were not required for viability and that carried P elements with inverted repeats of the target sites (FRTs) for the FLP site-specific recombinase. FLP-mediated unequal sister-chromatid exchange between inverted FRTs produced dicentric chromosomes at a high rate. The fate of the dicentric chromosome was evaluated in the mitotic cells of the male germline. We found that dicentric chromosomes break in mitosis, and the broken fragments can be transmitted. Some of these chromosome fragments exhibit dominant semilethality. Nonlethal fragments were broken at many sites along the chromosome, but the semilethal fragments were all broken near the original site of sister-chromatid fusion, and retained P element sequences near their termini. We discuss the implications of the recovery and behavior of broken chromosomes for checkpoints that detect double-strand break damage and the functions of telomeres in Drosophila.