Flies expressing apScer\UAS.cBa under the control of Scer\GAL4ptc-559.1 have an ectopic margin in the posterior part of the wing that has anterior identity. In flies with a mild phenotype the wing has a large distal nick and the proximal part develops normally. In the most extreme cases the wing is separated almost completely into two halves. One half consists of the anterior portion of the wing, including the anterior margin characterised by a triple row of bristles. Most of the other half represents the posterior portion of the wing. Two pouch-like structures are formed in the wing discs in these flies. Two incomplete pouch-like structures which are fused in the proximal region are formed in the wing discs in flies expressing apScer\UAS.cBa under the control of Scer\GAL4salm-459.2.