STRUCTURE AND ORGANIZATION 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-re pressor-like'' proteins during the past few millions years. In both sp ecies, they are tandemly amplified in a single euchromatic gene cluste r at equivalent chromosomal positions. In contrast, Drosophila madeire nsis, an endemic species that is very closely related to both D. subob scura and D. guanche, harbours an additional P homologous site. Severa l mechanisms can be invoked to explain the generation of the new site in this species. In this work we present several molecular and cytolog ical data in order to elucidate the possible evolutionary origin of th e P derivatives of D. madeirensis.