Following the sequencing of the human genome in 2001, genetic variation between people was largely pinned on simple sequence differences known as single-nucleotide polymorphisms, or SNPs. This led to large-scale SNP-mapping ventures, such as the International HapMap Project, to identify regions of the genome underlying phenotypic variation and disease susceptibility. But SNPs are only part of the picture. Recently, scientists are realizing that structural differences - including deletions, duplications, inversions, and copy-number variants - encompass millions of bases of DNA, and are at least as important as SNPs in contributing to genomic variation in humans.
In 2004, two landmark studies showed that gains or losses of large swaths of DNA - known as copy number variants (CNVs) - are common features of the human genome. These first genome-wide studies identified a few hundred CNVs, but because of the techniques used, researchers could detect only large-scale differences of roughly 50 kb ...
