Fig. 2

Null Distributions. Blue histograms represent the binned R² values for each of 10,000 sets of resampled SNPs regressed on an environmental variable. Each resampled set contains random SNPs that match the number of risk alleles and global allele frequency of the risk alleles for that disease. Red lines indicate values of R², adjusted as in Methods, with 0.45 for type 2 diabetes on distance from Africa (a) and 0.03 for celiac disease on longitude (b). Before adjustment, the R² values were 0.69 for type 2 diabetes on distance from Africa and 0.13 for celiac disease on longitude. The null distributions for these two diseases are different because each null distribution is created using resampled sets that are matched for number and global allele frequency of the risk alleles. Our analysis included 15 risk alleles for type 2 diabetes and 26 for celiac disease