Editing Selfish genetic element (section)

=== Homing endonucleases ===
[[File:Homing endonucleases.png|thumb|Homing endonucleases can recognize a target sequence, cut it, and then use its own sequence as a template during double strand break repair. This converts a heterozygote into a homozygote.]]
A phenomenon closely related to segregation distortion is [[homing endonuclease]]s.<ref name=":15">{{cite journal | vauthors = Burt A | title = Site-specific selfish genes as tools for the control and genetic engineering of natural populations | journal = Proceedings. Biological Sciences | volume = 270 | issue = 1518 | pages = 921–8 | date = May 2003 | pmid = 12803906 | pmc = 1691325 | doi = 10.1098/rspb.2002.2319 }}</ref><ref>{{cite journal | vauthors = Burt A, Koufopanou V | title = Homing endonuclease genes: the rise and fall and rise again of a selfish element | journal = Current Opinion in Genetics & Development | volume = 14 | issue = 6 | pages = 609–15 | date = December 2004 | pmid = 15531154 | doi = 10.1016/j.gde.2004.09.010 }}</ref><ref>{{cite journal | vauthors = Windbichler N, Menichelli M, Papathanos PA, Thyme SB, Li H, Ulge UY, Hovde BT, Baker D, Monnat RJ, Burt A, Crisanti A | title = A synthetic homing endonuclease-based gene drive system in the human malaria mosquito | journal = Nature | volume = 473 | issue = 7346 | pages = 212–5 | date = May 2011 | pmid = 21508956 | pmc = 3093433 | doi = 10.1038/nature09937 | bibcode = 2011Natur.473..212W }}</ref> These are enzymes that cut DNA in a sequence-specific way, and those cuts, generally double-strand breaks, are then "healed" by the regular DNA repair machinery. Homing endonucleases insert themselves into the genome at the site homologous to the first insertion site, resulting in a conversion of a heterozygote into a homozygote bearing a copy of the homing endonuclease on both homologous chromosomes. This gives homing endonucleases an allele frequency dynamics rather similar to a segregation distortion system, and generally unless opposed by strong countervailing selection, they are expected to go to fixation in a population. [[CRISPR|CRISPR-Cas9]] technology allows the artificial construction of homing endonuclease systems. These so-called "gene drive" systems pose a combination of great promise for biocontrol but also potential risk.<ref name=":16">Gantz VM, Bier E. Genome editing. The mutagenic chain reaction: a method for converting heterozygous to homozygous mutations. Science. 2015;348: 442–444.</ref><ref name=":17">{{cite journal | vauthors = Esvelt KM, Smidler AL, Catteruccia F, Church GM | title = Concerning RNA-guided gene drives for the alteration of wild populations | journal = eLife | volume = 3 | date = July 2014 | pmid = 25035423 | pmc = 4117217 | doi = 10.7554/eLife.03401 | doi-access = free }}</ref>