Editing Non-coding DNA (section)

===Junk DNA===
{{Main|Junk DNA}}
Junk DNA is DNA that has no biologically relevant function such as pseudogenes and fragments of once active transposons. Bacteria and viral genomes have very little junk DNA<ref>{{cite journal | vauthors = Gil R, and Latorre A | date = 2012 | title = Factors behind junk DNA in bacteria | journal = Genes | volume = 3 | issue = 4 | pages = 634–650 | doi = 10.3390/genes3040634 | pmid = 24705080 | pmc = 3899985 | doi-access = free }}</ref><ref>{{Cite journal |last1=Brandes |first1=Nadav |last2=Linial |first2=Michal |date=2016 |title=Gene overlapping and size constraints in the viral world |journal=Biology Direct |language=en |volume=11 |issue=1 |pages=26 |doi=10.1186/s13062-016-0128-3 |pmid=27209091 |pmc=4875738 |issn=1745-6150 |doi-access=free }}</ref> but some eukaryotic genomes may have a substantial amount of junk DNA.<ref name="PalazzoGregory2014">{{cite journal | vauthors = Palazzo AF, Gregory TR | title = The case for junk DNA | journal = PLOS Genetics | volume = 10 | issue = 5 | pages = e1004351 | date = May 2014 | pmid = 24809441 | pmc = 4014423 | doi = 10.1371/journal.pgen.1004351 | doi-access = free }}</ref> The exact amount of nonfunctional DNA in humans and other species with large genomes has not been determined and there is considerable controversy in the scientific literature.<ref>{{cite journal | last = Morange | first = Michel | date = 2014 | title = Genome as a Multipurpose Structure Built by Evolution | journal = Perspectives in Biology and Medicine | volume =  57 | issue = 1 | pages = 162–171 |  doi = 10.1353/pbm.2014.0008 | pmid = 25345709 | s2cid = 27613442 | url = https://hal.archives-ouvertes.fr/hal-01480552/file/ARTICLE%20ENCODE%20MM%2070114%20corrige%C2%A6%C3%BC.pdf }}</ref><ref>{{cite journal | vauthors = Haerty W, and Ponting CP | title = No Gene in the Genome Makes Sense Except in the Light of Evolution. | year = 2014 | journal = Annual Review of Genomics and Human Genetics | volume =25 | pages = 71–92 | doi = 10.1146/annurev-genom-090413-025621| pmid = 24773316 | doi-access = free }}</ref>

The nonfunctional DNA in bacterial genomes is mostly located in the intergenic fraction of non-coding DNA but in eukaryotic genomes it may also be found within [[introns]]. There are many examples of functional DNA elements in non-coding DNA, and it is erroneous to equate non-coding DNA with junk DNA.