GENETIC-EVIDENCE FOR REPRESSION OF SOMATIC P-ELEMENT MOVEMENTS IN DROSOPHILA-MELANOGASTER CONSISTENT WITH A ROLE FOR THE KP ELEMENT

The P family of transposable elements in Drosophila melanogaster has, since its introduction into D. melanogaster populations in this centur y, diversified into a number of internally deleted forms. One of these , the KP element, is abundant in the genomes of flies from populations from Asia, Europe and Africa. There is some evidence that this sequen ce can act as a repressor of transposition. We have studied a mutation , singed(very weak)(sn(vw)), in which a KP element is one of two P ele ments inserted into the 5' exon of the X-linked singed gene. These ele ments can be mobilized by a trans-acting dominant mutation, Mo, with a maternal effect, on the second chromosome. The rate of somatic revers ion of sn(vw) induced by Mo is reduced threefold if the mother herself possesses sn(vw) on her X chromosomes. This implies that sn(vw) may b e responsible for a form of repression of P element movements. The cau se of this effect may be related to transcription of the KP element in sn(vw). However, an effect of other genomic P elements in the repress ion of somatic reversion of sn(vw) cannot be entirely excluded.