Fig. 1. Diagram of the BX-C. The multicolored bar represents the DNA of the BX-C. Map coordinate numbering follows the numbering established by the original Drosophila Genome Project sequencing of the BX-C (Martin et al., 1995). The three BX-C homeotic genes, Ubx, abd-A and Abd-B are indicated below this bar (with exons indicated by the black horizontal bars and introns indicated by the diagonal lines connecting the bars). The individual cis-regulatory domains are indicated by the different colored regions on this bar. The orange and red regions (abx/bx and bxd/pbx) control Ubx expression. The regions shaded in blue (iab-2, 3 and 4) control abd-A expression. And the regions shaded in green (iab-5 through iab-8) control Abd-B expression. The corresponding adult segments affected by mutations in each cis-regulatory region are indicated on the diagram of the adult fly using the same color code.