Spatial structure of SNP distributions

The figure above is taken from A model-based approach for analysis of spatial structure in genetic data (Nature Genetics). The paper develops a novel method for extracting geographical origin from SNP data. (However, the panels I display show the results of standard PCA analysis.) An interesting aspect of the method in the paper is that it allows to identify specific genes with a large spatial gradient in allele frequency, which could be a signal for selection. Here is the distribution of scores on this gradient measure (e.g., LCT controls lactose tolerance). Someone should look up the SPA scores of height-associated alleles from GIANT. (Table 4 in the Supplement lists the top 0.1% of SNPs by SPA score.) Click images for larger versions.