The definition of structural variation (SV) has evolved as new technologies capture an ever-widening spectrum of alleles. SVs are sometimes defined operationally as deletions, duplications, insertions and inversions that are greater than 1 kb in size (Alkan et al., 2011; Zhang et al., 2009b), but in reality SVs follow a continuous distribution of size (Figure 1A) and can include simple insertion/deletion or complex rearrangements (Figure 1B).
