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 compound, organic molecules composed of a nitrogenous base, a pentose sugar and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both o ...

sequences present in multiple copies in the

genome 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 genes, other functional regions of the genome such as ...

. Generally, a direct repeat occurs when a sequence is repeated with the same pattern downstream. There is 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. ::: ::: 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), also transposon, or jumping gene, is a type of mobile genetic element, a nucleic acid sequence in DNA that can change its position within a genome. The discovery of mobile genetic elements earned Barbara McClinto ...

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 o ...

s (LTRs) on

retroviruses A retrovirus is a type of virus that inserts a DNA copy of its RNA genome into the DNA of a host cell that it invades, thus changing the genome of that cell. After invading a host cell's cytoplasm, the virus uses its own reverse transcriptase ...

. Direct terminal repeats are in the same direction and inverted terminal repeats are opposite to each other in direction. *

Tandem repeats In genetics, tandem repeats occur in DNA when a pattern of one or more nucleotides is repeated and the repetitions are directly adjacent to each other, e.g. ATTCG ATTCG ATTCG, in which the sequence ATTCG is repeated three times. Several protein ...

(tandem repeat sequences) are repeated copies which lie adjacent to each other. These can also be direct or inverted repeats. 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 Transfer ribonucleic acid (tRNA), formerly referred to as soluble ribonucleic acid (sRNA), is an adaptor molecule composed of RNA, typically 76 to 90 nucleotides in length (in eukaryotes). In a cell, it provides the physical link between the gene ...

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 that occur in multiple copies throughout the genome. In many organisms, a significant fraction of the genomic DNA is repetitive, with ov ...

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 A microsatellite is a tract of repetitive DNA in which certain Sequence motif, DNA motifs (ranging in length from one to six or more base pairs) are repeated, typically 5–50 times. Microsatellites occur at thousands of locations within an organ ...

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, ...

plays a prominent role in the formation of direct trinucleotide repeat expansions. Such repeat expansions underlie several neurological and developmental disorders in humans.

Homologous recombination

In directly repeated sequences of the

tobacco Tobacco is the common name of several plants in the genus '' Nicotiana'' of the family Solanaceae, and the general term for any product prepared from the cured leaves of these plants. More than 70 species of tobacco are known, but the ...

plant

, DNA double-strand breaks can be efficiently repaired by

homologous recombination Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in Cell (biology), cellular organi ...

between the repeated sequences.

References

Repetitive DNA sequences Genetics {{genetics-stub

Types

Microsatellite DNA

Homologous recombination

See also

References