GROSS CHROMOSOME REARRANGEMENTS MEDIATED BY TRANSPOSABLE ELEMENTS IN DROSOPHILA-MELANOGASTER

A combination of cytogenetic and molecular analyses has shown that sev eral different transposable elements are involved in the restructuring of Drosophila chromosomes. Two kinds of elements, P and hobo, are esp ecially prone to induce chromosome rearrangements. The mechanistic det ails of this process are unclear, but, at least some of the time, it s eems to involve ectopic recombination between elements inserted at dif ferent chromosomal sites; the available data suggest that these ectopi c recombination events are much more likely to occur between elements in the same chromosome than between elements in different chromosomes. Other Drosophila transposons also appear to mediate chromosome restru cturing by ectopic recombination; these include the retrotransposons B EL, roo, Doc and I and the foldback element FB. In addition, two retro transposons, HeT-A and TART, have been found to be associated specific ally with the ends of Drosophila chromosomes. Very limited data indica te that transposon-mediated chromosome restructuring is occurring in n atural populations of Drosophila. This suggests that transposable elem ents may help to shape the structure of the Drosophila genome and impl ies that they may have a similar role in other organisms.