Interstitial telomeric-like repeat insertion without modification of the flanking sequences. (A,B) Two examples of this type of insertion. A short portion of the DNA sequence of the ITS loci in different primate species is shown. (HSA) Homo sapiens; (PPA) Pan paniscus; (GGO) Gorilla gorilla; (PPY) Pongo pygmaeus; (HLA) Hylobates lar; (PCR) Presbytis cristata; (PAN) Papio anubis; (MMU) Macaca mulatta. The inserted nucleotides are shown in red. In the locus presented in A, the ITS is present in human, chimpanzee, and gorilla and absent in the more distant primates; the ITS presented in B is human-specific. (C) A model for this type of insertion. The telomeric repeats (red boxes) are inserted at a blunt double-strand break site either by the telomerase enzyme or via the capture of a double-stranded telomeric fragment. The human ITS locus in A is the AL033381 sequence from Chromosome 6p24; in B the AC039056 sequence from 15q14.