Editing Gene duplication (section)

===Neofunctionalization===

{{Main|Neofunctionalization}}

Gene duplications are an essential source of genetic novelty that can lead to evolutionary innovation. Duplication creates genetic redundancy, where the second copy of the gene is often free from [[purifying selection|selective pressure]]—that is, [[mutation]]s of it have no deleterious effects to its host organism.  If one copy of a gene experiences a mutation that affects its original function, the second copy can serve as a 'spare part' and continue to function correctly.  Thus, duplicate genes accumulate mutations faster than a functional single-copy gene, over generations of organisms, and it is possible for one of the two copies to develop a new and different function. Some examples of such neofunctionalization is the apparent mutation of a duplicated digestive gene in a family of [[Notothenioidei|ice fish]] into an antifreeze gene and duplication leading to a novel snake venom gene<ref name=VLynch>{{cite journal | vauthors = Lynch VJ | title = Inventing an arsenal: adaptive evolution and neofunctionalization of snake venom phospholipase A2 genes | journal = BMC Evolutionary Biology | volume = 7 | pages = 2 | date = January 2007 | pmid = 17233905 | pmc = 1783844 | doi = 10.1186/1471-2148-7-2 | doi-access = free }}</ref> and the synthesis of 1 beta-hydroxytestosterone in pigs.<ref name=Conant>{{cite journal | vauthors = Conant GC, Wolfe KH | title = Turning a hobby into a job: how duplicated genes find new functions | journal = Nature Reviews. Genetics | volume = 9 | issue = 12 | pages = 938–50 | date = December 2008 | pmid = 19015656 | doi = 10.1038/nrg2482 | s2cid = 1240225 }}</ref>

Gene duplication is believed to play a major role in [[evolution]]; this stance has been held by members of the scientific community for over 100 years.<ref name="Taylor_Raes_2004">{{cite journal | vauthors = Taylor JS, Raes J | title = Duplication and divergence: the evolution of new genes and old ideas | journal = Annual Review of Genetics | volume = 38 | pages = 615–43 | year = 2004 | pmid = 15568988 | doi = 10.1146/annurev.genet.38.072902.092831 }}</ref> [[Susumu Ohno]] was one of the most famous developers of this theory in his classic book ''Evolution by gene duplication'' (1970).<ref name="Ohno_1970">{{cite book |last=Ohno |first=S. |year=1970 |title=Evolution by gene duplication|publisher=[[Springer Science+Business Media|Springer-Verlag]]| isbn=978-0-04-575015-3 |author-link=Susumu Ohno}}</ref>  Ohno argued that gene duplication is the most important evolutionary force since the emergence of the [[common descent|universal common ancestor]].<ref name="Ohno_1967">{{cite book |last=Ohno |first=S. |year=1967 |title=Sex Chromosomes and Sex-linked Genes|url=https://archive.org/details/sexchromosomesse0001ohno |url-access=registration |publisher=Springer-Verlag |isbn=978-91-554-5776-1 }}</ref>
Major [[Polyploidy|genome duplication]] events can be quite common. It is believed that the entire [[yeast]] [[genome]] underwent duplication about 100 million years ago.<ref name="Kellis_2004">{{cite journal | vauthors = Kellis M, Birren BW, Lander ES | title = Proof and evolutionary analysis of ancient genome duplication in the yeast Saccharomyces cerevisiae | journal = Nature | volume = 428 | issue = 6983 | pages = 617–24 | date = April 2004 | pmid = 15004568 | doi = 10.1038/nature02424 | bibcode = 2004Natur.428..617K | s2cid = 4422074 }}</ref>  [[Plant]]s are the most prolific genome duplicators.  For example, [[wheat]] is hexaploid (a kind of [[polyploid]]), meaning that it has six copies of its genome.