Figure 2.

Candidate gene approaches (A) have only involved a few variants in one to several dozen genes. Given a genome of roughly 25,000 genes, this represents a very small sampling (∼0.01% or less). GWAS (B) samples a much larger component of the genome, probing more than 90% of the genes, but it still only examines less than 5% of the over 50 million reference SNPs (http://www.ncbi.nlm.nih.gov/mailman/pipermail/dbsnp-announce/2012q2/000123.html) curated as of June, 2012. As costs come down, exome (not shown) and whole-genome sequencing (C) provide the potential to capture all variation in study subjects.