Direct repeats are a type of genetic sequence that consists of two or more repeats of a specific sequence. In other words, the direct repeats are

nucleotide Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecules wi ...

sequences present in multiple copies in the

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...

. Generally, a direct repeat occurs when a sequence is repeated with the same pattern downstream. There is and no

reverse complement In molecular biology, complementarity describes a relationship between two structures each following the lock-and-key principle. In nature complementarity is the base principle of DNA replication and transcription as it is a property shared b ...

associated with a direct repeat. It may or may not have intervening nucleotides. The nucleotide sequence written in bold characters signifies the repeated sequence. ::: ::: Linguistically, a typical direct repeat is comparable to saying "bye-bye".

Types

There are several types of repeated sequences : *Interspersed (or dispersed) DNA repeats (interspersed repetitive sequences) are copies of

transposable elements A transposable element (TE, transposon, or jumping gene) is a nucleic acid sequence in DNA that can change its position within a genome, sometimes creating or reversing mutations and altering the cell's genetic identity and genome size. Trans ...

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 repeat A long terminal repeat (LTR) is a pair of identical sequences of DNA, several hundred base pairs long, which occur in eukaryotic genomes on either end of a series of genes or pseudogenes that form a retrotransposon or an endogenous retrovirus or ...

s (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 repeats occur in DNA when a pattern of one or more nucleotides is repeated and the repetitions are directly adjacent to each other. Several protein domains also form tandem repeats within their amino acid primary structure, such as armadil ...

(tandem repeat sequences) are repeated copies which lie adjacent to each other. These can also be direct or

inverted repeats An inverted repeat (or IR) is a single stranded sequence of nucleotides followed downstream by its reverse complement. The intervening sequence of nucleotides between the initial sequence and the reverse complement can be any length including zero. ...

. The

ribosomal RNA Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA which is the primary component of ribosomes, essential to all cells. rRNA is a ribozyme which carries out protein synthesis in ribosomes. Ribosomal RNA is transcribed from ribosomal ...

and transfer RNA genes belong to the class of middle repetitive DNA.

Microsatellite DNA

A tract of

repetitive DNA Repeated sequences (also known as repetitive elements, repeating units or repeats) are short or long patterns of nucleic acids (DNA or RNA) that occur in multiple copies throughout the genome. In many organisms, a significant fraction of the geno ...

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 DNA mismatch repair (MMR) is a system for recognizing and repairing erroneous insertion, deletion, and mis-incorporation of nucleobase, bases that can arise during DNA replication and Genetic recombination, recombination, as well as DNA repair, r ...

plays a prominent role in the formation of direct trinucleotide repeat expansions.Richard GF. The Startling Role of Mismatch Repair in Trinucleotide Repeat Expansions. Cells. 2021 Apr 26;10(5):1019. doi: 10.3390/cells10051019. PMID: 33925919; PMCID: PMC8145212 Such repeat expansions underlie several neurological and developmental disorders in humans.

References

Repetitive DNA sequences Genetics {{genetics-stub

Types

Microsatellite DNA

See also

References