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.
KeywordsBithorax Complex cis-regulation homeotic loci Drosophila imaginal discs sexual dimorphism
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