Inflation of p values was revealed by preliminary examination of the quantile-quantile (Q-Q) plot (Figure S3). The genomic inflation factor (GIF), calculated by computing the median of the χ2 statistics divided by the median of the central χ2 distribution with df =1, was 1.25. In order to control for this inflation, we used the method of the Genomic Control27 with a λ of 1.25. In particular, we re-computed the level of association with each marker by dividing the observed χ2 with inflation factor λ of 1.25. We verified that these new, inflation corrected p values had a GIF of 1, indicating no further inflation.
