Fig. 7. Ectopic btd expression induces transformation of dorsal disc patterns into the corresponding ventral discs. (A) Head of an ey-Gal4/UAS-btd fly completely lacking eyes and showing duplication of antennae. The duplication is clear on the left side but not on the right because duplicated antennae tend to fuse. (B) Clone of btd-expressing cells marked with f³⁶ (arrow) showing transformation towards antenna. Compare with the normal antenna towards the left. (C) Thorax of a nub-Gal4/UAS-btd fly. Wings and halteres are totally replaced by leg structures. Although overall leg patterns observed in this genotype are abnormal, the individual pattern elements of leg identity can be recognised. The inset shows a high magnification of a region of a transformed wing: all the bristles present an associated bract, a typical feature of leg bristles (arrows). Note that the bracts are similarly orientated with respect to the bristles in all cases, indicating that the ectopic leg patterns have acquired normal polarity. (D) Side view of an omb-Gal4/UAS-btd fly illustrating the transformation towards leg of most of the wing (halteres are also transformed although they are not visible). Although there are supernumerary leg structures, they often form local arrangements that reproduce normal leg patterns. Arrows indicate tibia-like and tarsus-like patterns. (E) A large clone of btd-expressing cells in the wing about to sort themselves from the wing cells. (F) Higher magnification of the clone in E showing the autonomously generated leg pattern and the presence of an edge bristle, which is characteristic of the midleg (arrow).

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