KP elements repress P‐induced hybrid dysgenesis in Drosophila melanogaster

Molecular and genetic analysis has revealed a specific P factor deletion derivative (the KP element) which is able to repress P‐induced hybrid dysgenesis. All naturally occurring strains lacking the P cytotype (M′) that were examined, throughout the world contain up to 30 copies of KP per haploid genome together with complete P factors. The KP element is derived from the P factor by an internal deletion of 1753 bp removing nucleotides 808‐2560 and is transcribed to yield an abundant 0.8‐kb poly(A)+ RNA with the coding capacity for an in‐frame 207 amino acid polypeptide. Genetic crosses show that KP elements preferentially accumulate in the presence of P factors and suppress hybrid dysgenesis. Suppression is transmitted through both sexes and is thus distinct from the maternally transmitted P cytotype mode of suppression. The spread of KP elements is probably due to the continual selection of individuals with the highest numbers of KP elements in which P‐induced hybrid dysgenesis is suppressed.