Fig. 2. Abd-B is needed for the formation of the embryonic genital disc. Anterior is to the top. (A) Late stage 15 hdc-lacZ embryo showing the three clusters of cells that will form the genital disc. (B) Stage 15 Abd-B^M5 hdc-lacZ homozygous embryo. The embryonic genital disc is formed by fewer cells in the mutant than in the wild type. (C) Similar stage embryo of the genotype Abd-B^Uab1/Abd-B^M1 hdc-lacZ. The genital disc is disorganized and includes fewer cells than the wild type does. (D) Stage 15 Abd-B^M1 hdc-lacZ homozygous embryo. Some ß-galactosidase-expressing cells are scattered (out of focus) and only the posterior cluster remains (arrow). (E,F) In Abd-B^M1 hdc-lacZ homozygous embryos, Dll is ectopically activated in some posterior cells (arrows, E; red, F); hdc is marked in green in F. vc, ventral cord.