The Affymetrix and Illumina expression probes were pooled together and grouped into GO categories using annotation information downloaded from the manufacturer's website. We considered that a probe could be mapped as an eQTL if it represents one gene symbol among the 14,177 genes in Table 1; i.e., the probe can be mapped by either 1000 Genomes imputation SNPs on autosome or by genotyped SNPs on chromosome X. For each GO category, we calculated the percentage of probes mapped by eQTL, denoted as for the ith GO category. The Z-score for the ith GO category is , where is the overall percent of probes mapped by eQTL, is the standard deviation of the indicator variable whether a probe can be mapped or not, and is the number of probes for the ith GO category. The P-value is computed by comparing the Z-score with a standard normal distribution for one side test.
