The starting P{(-FRT)lacZ.HP}UbxHC184B element has been inverted and internally deleted, such that the remaining element is 690bp long, with 656bp from the 5' end of the starting element and 15bp from the 3' end, separated by 19bp of AT-rich sequence with no obvious homology to the starting element. The P-element promoter is retained at the 5' end as is the first 65bp of the Ecol\lacZ sequence. This P-element promoter points towards the distal end of the chromosome arm.
Heterozygotes show transformation of the first abdominal segment into a copy of the second abdominal segment. Homozygotes usually die as pharate adults. In exceptional homozygotes that do eclose, the tergite on the first abdominal segment resembles that of the second, third or fourth abdominal segments in size, pigmentation and bristle morphology. The first abdominal segment has a complete sternite (the first abdominal segment lacks a sternite in wild-type flies), which resembles that of the third or fourth abdominal segment in the number and orientation of bristles. The sternite of the second abdominal segment is also transformed to a more posterior identity. Homozygotes also show a thin band of cuticle between the thorax and abdomen, which in rare individuals is expanded on one side into a recognisable half tergite, similar to the normal tergites on the second through fourth abdominal segments (as judged by bristle morphology). This "extra" abdominal-like segment is probably derived from the third thoracic segment, which does not normally contribute to the adult dorsal cuticle. Homozygotes also have enlarged or missing halteres, are typically unable to flatten their wing blades and often have malformed legs. Homozygous third instar larvae often show subtle transformation of the denticle bands of the first abdominal segment towards the character of the wild-type second segment.
Distally directed transcripts from the P{(-FRT)lacZ.HP-ΔHH1}abd-AUab-HH1 insertion are detected in abd-AUab-HH1 embryos, which can extend for about 50kb. P cytotype can revert the abd-AUab-HH1 phenotype, indicating that the "Uab" phenotypes in this mutant are due to RNAs initiated at the P-element promoter in the P{(-FRT)lacZ.HP-ΔHH1}abd-AUab-HH1 insertion; abd-AUab-HH1/Harwich heterozygotes are virtually wild-type (whether the Harwich chromosomes are maternally or paternally derived) and crosses of abd-AUab-HH1 to π2 give partial suppression of the abd-AUab-HH1 phenotype. However, a MR-h12 stock gives no suppression of the abd-AUab-HH1 phenotype.