Alu repeat

Alu repeats, also known as Alu elements, form a family of short DNA intervals (about 300 bp long) that occur in primates; specifically, Alu elements occur around a million times on the human genome (thus making up 10.7% of all base pairs).

Alu repeats are retrotransposons, which means that they can create copies of themselves to be inserted elsewhere in the genome. The insertion of a new Alu repeat into a coding region is a common source of mutation in humans, and new Alu repeats have been linked with some genetic disorders. As a result, because Alu elements appear to serve no real practical purpose, they can be viewed as a genomic parasite of sorts.