Structure and organization of the P element related sequences in Drosophila madeirensis

The P element homologous sequences of the two closely related species Drosophila guanche and Drosophila subobscura represent a very special case of transposable-element derivatives. Although they have lost the regions known to be essential for P transposition by random mutations, all of them have selectively conserved the coding capacity for "P-repressor-like" proteins during the past few millions years. In both species, they are tandemly amplified in a single euchromatic gene cluster at equivalent chromosomal positions. In contrast, Drosophila madeirensis, an endemic species that is very closely related to both D. subobscura and D. guanche, harbours an additional P homologous site. Several mechanisms can be invoked to explain the generation of the new site in this species. In this work we present several molecular and cytological data in order to elucidate the possible evolutionary origin of the P derivatives of D. madeirensis.