Hemizygotes show an iab5,6,7 mutant phenotype: abdominal segments A5-A7 transform towards A4. Heterozygotes with Abd-B point or pseudopoint mutations cause a less severe mutant phenotype, with mixed A5/A6 identity in A6 and A7. Phenotype over Ubx^MX12, abd-A^M1, Abd-B^M8 is the same as when over Abd-B^-.

Heterozygous show a transformation of head structures into genital and abdominal structures; structures characteristic of the 7th or 8th abdominal segments as well as of the lateral plates of the genitalia can often be recognised in the head. In males the transformed head parts show the dark pigmentation characteristic of the male abdomen. The occiput, upper postorbita and facets are transformed most frequently, the vertex, frontorbita and frons are rarely transformed, and the lower postorbita, ptilinum and vibrissae are not transformed. Antennal structures are sometimes found in the middle of the eyes. Eye-antennal discs appear abnormal; the lateral part is flattened without any significant folding. The penetrance of the phenotype is nearly complete at 25^oC, somewhat lower at 18^oC, and significantly reduced at 29^oC. 84.2% of the progeny of heterozygous females show the head transformation phenotype, indicating that this mutation has a maternal enhancement effect. Homozygotes have reduced viability and are sterile. They also have abnormal head morphology; a small group of facets form instead of the eyes, and the occiput bristles, ocelli and antennae are missing.