Transheterozygous Usp7^kim1/Pc³ flies exhibit partial antenna to leg transformations. Usp7^kim1 strongly enhances the frequency and severity of a range of homeotic transformations caused by either Pc¹ or Pc³ flies. For example, wing-to-haltere transformations occur only very rarely in heterozygous Pc¹ or Pc³ flies. However, in combination with either hetero- or hemizygous Usp7^kim1, in respectively females or males, the penetrance of wing-to-haltere transformations is significantly increased. Depending on the combination of alleles, wing-to-haltere transformations occur in the majority or virtually all animals. Likewise, there is a strong increase in the frequency and extent of transformations of the fourth abdominal segment (A4) into the semblance of the fifth (A5), indicated by increased dark pigmentation of the A4. In males hemizygous for Usp7^kim1 and heterozygous for either Pc¹ or Pc³, the frequency of sex combs on the second leg (L2-L1) is strongly increased compared to flies harboring only a Pc¹ or Pc³ mutation. Females transheterozygous for Usp7^kim1 and Pc³ exhibit antenna to leg (Ant-L) transformations, which are not detected in Pc³ flies, but at a lower penetrance than in Usp7^KG06814/Pc³ flies.