Fig. 1. Map of the central region of the bithorax complex, showing the insertions associated with the Uab mutations. The horizontal line diagrams the DNA sequence, marked in kb according to the published sequence coordinates (Martin et al., 1995). The horizontal bars marked A-J above the sequence line indicate restriction fragments used to prepare probes for RNA in situ hybridization. Below the sequence line, the two previously characterized transcription units in the region are shown. The two triangles at the top left indicate the P element insertions from which the Uab alleles were derived. The bent arrows above the triangles indicate the direction of transcription in these elements. The triangles below the sequence line indicate the insertions in various Uab alleles. The G1 and L1 alleles are head-to-head duplications of the starting elements, the M1 and R1 alleles are inversions of the starting elements, and the HH1 allele is an inversion with an internal deletion.