Direct repeats are a type of genetic sequence that consists of two or more repeats of a specific sequence.[1] In other words, the direct repeats are
nucleotide sequences present in multiple copies in the
genome. Generally, a direct repeat occurs when a sequence is repeated with the same pattern downstream.[1] There is no inversion[clarification needed] and no
reverse complement associated with a direct repeat. It may or may not have intervening nucleotides. The nucleotide sequence written in bold characters signifies the repeated sequence.
5´ TTACGnnnnnnTTACG 3´
3´ AATGCnnnnnnAATGC 5´
Linguistically, a typical direct repeat is comparable to saying "bye-bye".[1]
Types
There are several types of repeated sequences :
Interspersed (or dispersed) DNA repeats (interspersed repetitive sequences) are copies of
transposable elements interspersed throughout the genome.
Flanking (or terminal) repeats (terminal repeat sequences) are sequences that are repeated on both ends of a sequence, for example, the
long terminal repeats (LTRs) on
retroviruses. Direct terminal repeats are in the same direction and inverted terminal repeats are opposite to each other in direction.
A tract of
repetitive DNA in which a motif of a few base pairs is tandemly repeated numerous times (e.g. 5 to 50 times) is referred to as
microsatellite DNA. Thus direct repeat tandem sequences are a form of microsattelite DNA. The process of
DNA mismatch repair plays a prominent role in the formation of direct trinucleotide repeat expansions.[2] Such repeat expansions underlie several neurological and developmental disorders in humans.[2]