signature, consistent with findings in other human genetics of gene expression studies [12,13]. The smaller trans eQTL signature likely reflects a lack of power to detect the small-to-moderate eQTL effects, given the sample size of this study in the context of testing 782,476 SNPs and profiling 39,280 expression traits. Other studies have noted strong heritability estimates for a majority of the expression traits that, when taken together with the small number of associations detected, suggests that expression in general is a complex trait under the control of many loci [21]. With the more stringent threshold required to constrain the FDR in searching for trans eQTL, the magnitude of the trans eSNP effects (mean R 2 = 0.19) was larger than the cis eSNP effects (mean R 2 = 0.14).
