Expression is vital for development; may be involved in transcriptional regulation. In embryos, muscle specific expression is required for segmental nerve b (SNb) motoneuron target recognition within ventral longitudinal muscles. Has a role in establishing and maintaining embryonic muscle attachments, adult sensory cell formation (macrochaetae) and morphogenesis of adult appendages (legs, antenna aristae and male external genitalia). Has a role in the morphogenesis of the class I dendritic neurons: selective expression of ab in class I da neurons plays a pivotal role in forming dendritic arbors, which are characteristic of the class I cells. The development of more complex arbors of class II-IV neurons depends on the absence of ab.

(UniProt, Q24174)

Vein L5 usually stops after posterior crossvein. Scutellar bristles usually fewer. Wing effect probably acts during contraction period (Waddington). Overlaps wild type. Expression more severe in females than in males and when pupal stage takes place at 20 than at 25. TSP during the first 10% of pupal stage. (Thompson, Bruni, Carbonaro, and Russo, 1988, DIS 67: 86). RK2.

Vein L5 does not reach margin. Scutellar bristles always fewer than wild type. Hairs parted down midline of thorax and abdomen. Supra-alar bristles sometimes absent. Coxae tend to be thickened. Males sterile and have rotated genitalia. ab/ab2 resembles ab/ab but has a stronger bristle effect. RK2.