Distribution and conservation of the foldback transposable element in Drosophila.

Foldback elements are a family of transposable elements described in Drosophila melanogaster. The members of this dispersed repetitive family have terminal inverted repeats that sometimes flank a central region. The inverted repeats of all the family members are homologous. The study of the distribution and conservation of the foldback elements in different Drosophila species shows that this distribution is different from that of the hybrid dysgenesis systems (PM and IR). Sequences homologous to foldback elements were observed by Southern blots and in situ hybridization in all species of the melanogaster subgroup and in some species of the montium and takahashii subgroups. The element was probably already present before the radiation of these subgroups. No evidence of horizontal transmission of the foldback element could be observed.