First time to touch SNP array. I have a set of SNP array downloaded from TCGA. Now I am interested in the SNP loci and trying to do the eQTL analysis. Would you guys provide a tutorial for this kind of work? How to get the SNP loci information, downloading from where or get from the array data? How to select SNP loci with good allele frequencies (TCGA level 1/2/3?)? Thanks.