Classification of genetic variants by composition. Schematic of sequence and structural variants compared to reference sequence. Sequence variation (indicated by red line) refers to single-nucleotide variants and small (less than 1 kb) indels. Structural variation includes inversions, translocations and copy-number variants, which result in the presence of a segment of DNA in variable numbers compared to the reference sequence, as in duplications, deletions or insertions. Adapted from .