a The structure of a canonical SVA consists of a (CCCTCT)n hexamer repeat, an Alu-like region consisting of two antisense Alu fragments and an intervening unique sequence, a variable number tandem repeat (VNTR), a SINE-R domain and a poly A-tail. The length of an intact SVA can vary depending on the number of repeats present in the hexamer and VNTR domains. SVAs are flanked by target site duplications (TSDs). b The proportion of the 81 reference SVA RIPs that belong to each of the seven subtypes of SVA. c The number of reference SVA RIPs that belong in each category of insertion allele frequency.