There was also moderate evidence for selection at the CHRNA5-A3-B4 locus. In particular, rs16969968, the SNP that encodes the missense mutation in α5, that is strongly associated with risk of nicotine dependence, lies in a sliding window exhibiting a high Tajima’s D score. The iHS analysis of this locus did not provide evidence for selection. This could indicate that the selective pressure exerted on this locus is older that that seen for the CHRNB3-A6 locus and as such has allowed extended haplotypes to be broken down by recombination. In this scenario, Tajima’s D would still be extreme while iHS scores in the region might be less so. This may be particularly true if the selective pressure being exerted on the CHRNB3-A6 locus is ongoing.
