Fig. 7. Conservation of the PTE sequence across Drosophila species. (A) An informal consensus tree (Crosby et al., 2007) illustrating evolutionary relationships among Drosophila species. (B) Sequence conservation levels for the 255 bp PTE and PTE 5' and PTE 3' (which represent the 255 bp regions 5' and 3' of the PTE with respect to Abd-B). For comparison, the conservation within the entire bithorax complex (BX-C) and the complete chromosomal control regions that direct Abdominal-B gene expression (iab8-iab5) and the IAB5 enhancer are also shown. Level of conservation between D. melanogaster and six other Drosophila species is indicated by color code: >90% red, 70-89% orange, 30-69% yellow, <30% green for different sequences. Conservation values were calculated using VISTA genome browser (see Materials and methods). Absolute conservation is the total percentage of D. melanogaster nucleotides that were conserved in the homologous region identified by VISTA alignment from the other species examined. (C) VISTA plots of the alignments indicate that the level of conservation is variable across the length of the PTE sequence. Overall, the PTE is less highly conserved than neighboring sequences or the non-genic regions in the BX-C, but there are two short, highly conserved sequences within it, a 24-mer (pink) and a 27-mer (green). The height of the peaks in the plots represents the level of conservation over a 24 bp window. Regions at least 24 bp long that are >80% conserved are indicated in cyan.