Cartoon of a 2-SNP block. Overlapping with the gene EPHA6, we called 2 SNPs on chromosome 3 about 300 bases apart in the CEU_TRIO member NA12878. Since both SNPs are heterozygous and they are within 500 bases of each other, this is a block on the genome. Three example reads are shown along with the bases they map to each SNP position. The table below shows frequencies. For example, there are 40 examples of reads that have a G at each SNP position.