P-element-mediated hybrid dysgenesis in Drosophila.

P-elements are transposable elements that carry genes for transposase activity that cause the elements to move, and repressor activity that prevents expression of transposase.

In a cross between a P-element-carrying female and a laboratory male [left], repressors in the maternally - derived cytoplasm repress expression of the maternally - inherited P elements. The resulting offspring show the wild-type phenotype.

In a cross between a P-element-carrying male and a laboratory female [right], repressors are absent in the maternally - derived cytoplasm. The two zygotes are chromsomally identical but cytoplasmically different. In the right-hand cross, P elements are activated and undergo transposition in the genome, causing release of mutator activity and a variety of dysgenic phenotypes in the offspring.