SNP Call Metrics. (a) SNP metrics of 92 1000 Genomes exome samples. The four figures are SNP number, Ts/Tv, dbSNP% and SNP density distributions respectively. SNPs were called and compared in the callable region with a variant read depth of at least 2. Previous studies have indicated that coding SNPs should have a Ts/Tv ratio of 3-4 . (b) SNP density in the 1000 Genomes Exome Project vs. the Exon Pilot. The SNP density was calculated as the number of SNPs discovered in each sample normalized against their callable region. The maximum and minimum SNP density in the 1000 Genomes exome data are 0.70/Kbp and 0.54/Kbp respectively, which are presented as two slope lines in the figure.