Short intron sequence alignment of the 2L chromosome arm

We analyzed whole-genome data (Langley C. et al., accepted 2012) of D. melanogaster (Release 1.0) from a sample of six inbred Malawi isofemale lines from the 50 genomes Drosophila Population Genomics Project (DPGP) (http://www.dpgp.org/ ). We downloaded (http://genome.ucsc.edu/ ) aligned single sequences of D. simulans, D. sechellia, D. erecta and D. yakuba (Release 5) (Begun et al., 2007; Clark et al., 2007) and combined them with the six D. melanogaster sequences into a multiple alignment for all autosomes. We used position 8 to 30 in short introns (less than 66 bp) as these are thought to be the least constrained sites in the Drosophila genome (Halligan and Keightley, 2006; Parsch et al., 2010). We used the D. melanogaster Flybase annotation (release 5.31) to identify these sites. Introns, which overlapped with coding regions were excluded from the analyses. Python scripts were written to concatenate all 23 considered positions per short intron into one alignment file for each chromosome arm.