Population differences of OR SPGs. A) Principal component analysis of the nonfunctional SNP genotypes. Each point represents a specific individual, colors as in Figure 5A. B) Normalized relative frequencies of the nonfunctional OR allele in the three ethnic populations, color-coded as in (A). This is shown for 25 ORs, selected to represent the highest inter-population variability (values are given in Additional file 5). This include 20 ORs belonging to class II (“tetrapod-like”), members of 15 subfamilies (e.g. 1E), and 5 ORs belonging to class I (“fish-like”), represented by members of 5 subfamilies (e.g. 51F). OR classification is as described . Colors as in Figure 5A.