Abstract
The P family of transposable elements in Drosophila melanogaster has, since its introduction into D. melanogaster populations in this century, 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 sequence can act as a repressor of transposition. We have studied a mutation, signed(very weak) (snVW), in which a KP element is one of two P elements inserted into the 5' exon of the X-linked singed gene. These elements can be mobilized by a trans-acting dominant mutation, Mo, with a maternal effect, on the second chromosome. The rate of somatic reversion of snvw induced by Mo is reduced threefold if the mother herself possesses snvw on her X chromosomes. This implies that snvw may be responsible for a form of repression of P element movement. The cause of this effect may be related to transcription of the KP element in snvw. However, an effect of other genomic P elements in the repression of somatic reversion of snvw cannot be entirely excluded.
