Genomic DNA was extracted from whole human blood using a commercial isolation kit (Gentra systems, Minneapolis, MN, USA) following the protocols detailed in the kit. Genotyping with Affymetrix Mapping 250k Nsp and Affymetrix Mapping 250k Sty arrays was performed at Vanderbilt Microarray Shared Resource using the standard protocol recommended by Affymetrix. Genotyping calls were determined from the fluorescent intensities using the DM (dynamic model-based) algorithm with a 0.33 P-value setting (18) as well as the B-RLMM algorithm (19). DM calls were used for quality control while the B-RLMM calls were used for all subsequent data analysis. B-RLMM clustering was performed with 94 samples per cluster.
