Figure 1

Genital disc morphology and Engrailed (EN) expression in D. melanogaster and representative species of three Diopsid genera: Teleopsis, Diasemopsis and Sphyracephala. All discs are bilaterally symmetrical. A. EN expression in male third instar genital disc (ventral view) of D. melanogaster. Note EN expression in two posterior lateral domains (arrowhead indicates the posterior domain on the left side of the disc) derived from the posterior compartments of the tenth abdominal segment. The larger anterior domains (arrow indicates the anterior domain on the left side of the disc) are derived from the posterior compartment of the ninth segment and give rise to parts of the male genitalia in the adult. B. EN expression in female third instar genital disc (ventral view) of D. melanogaster. As in the male disc, EN is expressed in two posterior lateral domains (arrowhead indicates the posterior domain on the left side of the disc) derived from the posterior compartments of the tenth abdominal segment. The larger anterior domains (arrow indicates the anterior domain on the left side of the disc) are derived from the posterior compartment of the eighth segment and give rise to parts of the female genitalia in the adult. C, E & G. Male third instar genital discs of T. dalmanni (C), D. meigenii (E) and S. beccarii (G). D, F & H. Female third instar genital discs of T. dalmanni (D), D. meigenii (F) and S. europaea (H). With the exception of the female discs in Sphyracephala, morphology and EN expression appear similar to that of the male and female discs in Drosophila. On each side of the disc EN is expressed in two domains, one anterior (arrows) and one more posterior and lateral (arrowheads). Anterior is uppermost in all panels.