Selection signatures in the OR genes. Correlation of non-synonymous to synonymous substitution rate (pN/pS) with Tajima’s D values for A, 364 intact OR genes and B, 439 single coding exon genes. Data are plotted for the European population, other populations in Additional file 1: Figure S4. The difference between the ORs and the control genes was tested using the Kolmogorov-Smirnov test yielding p = 1.936*10-24 for pN/pS, and p =2.26*10-5 for Tajima’s D. The yellow squares highlight regions which might act under non-neutral selection, top right with D>1, pN/pS>1.5 (balancing selection), and bottom left with Tajima’s D<−0.5 and pN/pS<0.5 (purifying selection). Additional file 1: Table S3 lists the 57 ORs found under purifying selection in all populations.