Maternally inherited transposon excision in Drosophila simulans.

A mutation in the white gene of Drosophila mauritiana resulting from insertion of the transposable element mariner exhibits genetic instability in germline and somatic cells. The instability is greatly enhanced in the presence of the trans-acting autosomal factor Mos, giving eye-color mosaics with pigmented sectors of tissue on an otherwise peach-colored background. The Mos factor, when introduced into the genome of the sibling species Drosophila simulans, exhibited a dramatic maternal effect on expression of the mosaic phenotype. When D. simulans mosaic females (heterozygous for Mos) were crossed with non-mosaic males, two distinct classes of mosaic offspring occurred, one resulting from a maternal effect in which the non-Mos offspring were nevertheless mosaic. The maternal effect was mediated by a product acting after fertilization, and was expressed to varying extents in different backcross strains.