Transabdominal, a dominant mutant of the Bithorax Complex, produces a sexually dimorphic segmental transformation in Drosophila.

Transabdominal (Tab), a dominant mutation in the Bithorax Complex (BX-C) of Drosophila, creates a sexually dimorphic pattern of segmental transformation that has complete penetrance and expressivity. Specific regions within the notum of the second thoracic segment (T2) are transformed into abdominal-like cuticle; thus, the Tab/ + notum has sets of short stripes that are black in males and only bordered with black in females. Also, Tab/ + abdominal tergites, A1-A6, inclusive, have small patches of A7-like tergite cuticle. Tab is inseparable from an 89E/90D inversion, whose DNA breakpoint in 89E is at +188 kb in the infra-abdominal-8 (iab-8) region of the BX-C. When probed with a pupal cDNA from the iab-7 region, labeling above background was not detected in wild-type wing discs but was detected in, and confined to, the notal region of Tab/ + wing discs. The Tab/ + phenotype is assumed to result from cis-overexpression of iab-7 in localized regions of segments T2-A6, inclusive.