CHROMOSOMAL DISTRIBUTION OF THE 412 RETROTRANSPOSON IN NATURAL-POPULATIONS OF DROSOPHILA-SIMULANS

The insertion site localization of the 412 retrotransposable element w as analysed by in situ hybridization to the polytene chromosomes of 57 individual genomes from 25 natural populations of Drosophila simulans . Tile 412 insertion sites along the chromosomes show a tendency to ag gregate in the distal and proximal ends of the 2R arm, and in several local regions along the 3R arm. The distribution of the 412 insertion sites, weighted by DNA content: along the chromosome arms reveals an o verall tendency for the site number to increase from the middle of the arm to the base and tip, with a decrease at the tips, especially pron ounced for the X chromosome. Such a distribution differs slightly from that of D. melanogaster, which globally shows an increase of the 412 site number from base to tip of the chromosome arms, indicating differ ing behaviour of the 412 element in the two species. These results are discussed in connection with the recombination rate along the chromos ome arms.