Direct repeat

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

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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.
* Tandem repeats (tandem repeat sequences) are repeated copies which lie adjacent to each other. These can also be direct or inverted repeats.[citation needed] The ribosomal RNA and transfer RNA genes belong to the class of middle repetitive DNA.

### Microsatellite DNA

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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]

## Homologous recombination

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In directly repeated sequences of the tobacco plant genome, DNA double-strand breaks can be efficiently repaired by homologous recombination between the repeated sequences.[3]

## See also

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* Inverted repeat

## References

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1. ^ a b c Ussery, David W.; Wassenaar, Trudy; Borini, Stefano (2009). "Word Frequencies and Repeats §Word Frequencies, Repeats, and Repeat-related Structures in Bacterial Genomes". Computing for Comparative Microbial Genomics: Bioinformatics for Microbiologists. Computational Biology. Vol. 8 (1 ed.). Springer. pp. 133–144\. doi:10.1007/978-1-84800-255-5_8. ISBN 978-1-84800-254-8.
2. ^ a b Richard, G. F. (2021). "The Startling Role of Mismatch Repair in Trinucleotide Repeat Expansions". Cells. 10 (5): 1019. doi:10.3390/cells10051019. PMC 8145212. PMID 33925919.
3. ^ Siebert R, Puchta H (May 2002). "Efficient repair of genomic double-strand breaks by homologous recombination between directly repeated sequences in the plant genome". Plant Cell. 14 (5): 1121–31\. doi:10.1105/tpc.001727. PMC 150611. PMID 12034901.

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Genetics: repeated sequence, transposon, gene duplication

Repeatome

Repeated sequence|

| Tandem repeats|

* Satellite DNA
* Variable number tandem repeat/Minisatellite
* Short tandem repeat/Microsatellite (Trinucleotide repeat disorders)
* Macrosatellite

|

Interspersed
repeat|

* Gene conversion
* Retrotransposon
* DNA transposon
* Polinton
* Helitron

Other|

* Inverted repeat
* Direct repeat

Transposon|

| Retrotransposon|

| SINEs|

* Alu sequence
* MIR

|

LINEs|

* LINE1
* LINE2

LTRs|

* HERV
* MER4
* retroposon

DNA transposon|

* Academ
* Crypton
* Dada
* EnSpm/CACTA
* Ginger1
* Ginger2
* Harbinger
* hAT
* Helitron
* IS3EU
* ISL2EU
* Kolobok
* Tc1/mariner
* Merlin
* MuDR
* Novosib
* P element
* PiggyBac
* Polinton
* Sola
* Transib
* Zator
* Zisupton

Gene duplication|

* Gene amplification
* Tandemly arrayed genes
* Ribosomal DNA
* Gene family
* Gene cluster
* Pseudogene

See also|

* Genomic island
* Pathogenicity island
* Symbiosis island
* Low copy repeats
* CRISPR
* Telomere
* Protein tandem repeats

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