Editing Repeated sequence (DNA) (section)

{{Short description|Patterns of nucleic acids that occur in multiple copies throughout the genome}}

'''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 over two-thirds of the sequence consisting of repetitive elements in humans.<ref>{{cite journal | vauthors = de Koning AP, Gu W, Castoe TA, Batzer MA, Pollock DD | title = Repetitive elements may comprise over two-thirds of the human genome | journal = PLOS Genetics | volume = 7 | issue = 12 | pages = e1002384 | date = December 2011 | pmid = 22144907 | pmc = 3228813 | doi = 10.1371/journal.pgen.1002384 | doi-access = free }}</ref> Some of these repeated sequences are necessary for maintaining important genome structures such as [[telomere]]s or [[centromere]]s.<ref name=Lower19>{{cite journal | vauthors = Lower SE, Dion-Côté AM, Clark AG, Barbash DA | title = Special Issue: Repetitive DNA Sequences | journal = Genes | volume = 10 | issue = 11 | pages = 896 | date = November 2019 | pmid = 31698818 | pmc = 6895920 | doi = 10.3390/genes10110896 | doi-access = free }}</ref>

Repeated sequences are categorized into different classes depending on features such as structure, length, location, origin, and mode of multiplication. The disposition of repetitive elements throughout the genome can consist either in directly adjacent arrays called [[tandem repeat]]s or in repeats dispersed throughout the genome called [[interspersed repeat]]s.<ref>{{Cite web |title=Repeated Sequence (DNA) — an overview |work=ScienceDirect Topics |url=https://www.sciencedirect.com/topics/neuroscience/repeated-sequence-dna |access-date=2022-10-04 |publisher=ScienceDirect}}</ref> Tandem repeats and interspersed repeats are further categorized into subclasses based on the length of the repeated sequence and/or the mode of multiplication.

While some repeated DNA sequences are important for cellular functioning and genome maintenance, other repetitive sequences can be harmful. Many repetitive DNA sequences have been linked to human diseases such as Huntington's disease and Friedreich's ataxia. Some repetitive elements are neutral and occur when there is an absence of selection for specific sequences depending on how transposition or [[Chromosomal crossover|crossing over]] occurs.<ref name=Lower19 /> However, an abundance of neutral repeats can still influence genome evolution as they accumulate over time. Overall, repeated sequences are an important area of focus because they can provide insight into human diseases and genome evolution.<ref name=Lower19 />