Interactions between transposable elements for insertion in the Drosophila melanogaster genome.

Using in situ hybridization to polytene salivary gland chromosomes, we have registered the co-occurrences of insertions of the four mobile elements, copia, mdg-1, I and P in the whole genomes of 17 highly-inbred lines of Drosophila melanogaster (the insertions in the centromeric regions were excluded); these elements differ in structure, DNA sequence and profile of developmental transcription. The mdg-1 and P elements tend to avoid each other on the X chromosomes but not on the autosomes; copia and mdg-1, two copia-like elements, show an excess of co-occurrences on the 2L and 3R chromosome arms but not on the X chromosomes. The pairs mdg-1/I, I/copia, I/P and copia/P do not show any kind of interaction. Populational studies are thus necessary to obtain complete accurate information on interactions between transposable elements for their sites of insertion in a genome.