Editing Hybrid (biology) (section)

==Biology==

===Expression of parental traits===
[[File:Exotic Pheasant (400938368).jpg|thumb|Hybrid between [[Lady Amherst's pheasant]] (''Chrysolophus amherstiae'') and another species, probably [[golden pheasant]] (''Chrysolophus pictus'')]]

When two distinct types of organisms breed with each other, the resulting hybrids typically have intermediate traits (e.g., one plant parent has red flowers, the other has white, and the hybrid, pink flowers).<ref name="M2006">{{cite book |last=McCarthy |first=Eugene M. |date=2006 |title=Handbook of Avian Hybrids of the World |publisher=Oxford University Press |pages=16–17}}</ref> Commonly, hybrids also combine traits seen only separately in one parent or the other (e.g., a [[bird hybrid]] might combine the yellow head of one parent with the orange belly of the other).<ref name="M2006" />

{{anchor|Interspecific hybrid}}

===Mechanisms of reproductive isolation===
{{main|Reproductive isolation}}

Interspecific hybrids are bred by mating individuals from two species, normally from within the same genus. The offspring display traits and characteristics of both parents, but are often [[Sterility (physiology)|sterile]], preventing gene flow between the species.<ref>{{cite book |last=Keeton |first=William T. |date=1980 |title=Biological Science |location=New York |publisher=Norton |isbn=9780393950212 |page=800}}</ref> Sterility is often attributed to the different number of chromosomes between the two species. For example, [[donkey]]s have 62 [[chromosomes]], [[horse]]s have 64 chromosomes, and [[mule]]s or [[hinny|hinnies]] have 63 chromosomes. Mules, hinnies, and other normally sterile interspecific hybrids cannot produce viable gametes, because differences in chromosome structure prevent appropriate pairing and segregation during [[meiosis]], meiosis is disrupted, and viable sperm and eggs are not formed. However, fertility in female mules has been reported with a donkey as the father.<ref>{{cite journal |pmid=3378453 |date=1988 |last1=Rong |first1=R. |last2=Chandley |first2=A. C.|last3=Song |first3=J. |last4=McBeath |first4=S. |last5=Tan |first5=P. P. |last6=Bai |first6=Q. |last7=Speed |first7=R. M. |title=A fertile mule and hinny in China |journal=Cytogenetics and Cell Genetics |volume=47 |issue=3 |pages=134–9 |doi=10.1159/000132531}}</ref>

A variety of mechanisms limit the success of hybridization, including the large genetic difference between most species. Barriers include morphological differences, differing times of fertility, mating behaviors and cues, and physiological rejection of sperm cells or the developing embryo. Some act before fertilization; others after it.<ref>{{cite journal |last1=Baker |first1=H. G. |date=1959 |title=Reproductive methods as factors in speciation in flowering plants |journal=Cold Spring Harb Symp Quant Biol |volume=24 |pages=177–191 |doi=10.1101/sqb.1959.024.01.019 |pmid=13796002}}</ref><ref>{{Cite journal |doi=10.1038/hdy.1986.135 |last1=Barton |first1=N. |last2=Bengtsson |first2=B. O. |date=1986 |title=The barrier to genetic exchange between hybridising populations |journal=Heredity |volume=57 |issue=3 |pages=357–376 |pmid=3804765 |s2cid=28978466 |doi-access=free|bibcode=1986Hered..57..357B }}</ref><ref>{{cite book |last=Strickberger |first=M. |date=1978 |title=Genética |language=es |publisher=Omega |location=Barcelona |pages=874–879 |isbn=9788428203692}}</ref><ref>{{cite book |last=Futuyma |first=D. |date=1998 |title=Evolutionary Biology |edition=3rd |publisher=Sinauer |location=Sunderland}}</ref>

In plants, some barriers to hybridization include blooming period differences, different pollinator vectors, inhibition of pollen tube growth, somatoplastic sterility, cytoplasmic-genic male sterility and structural differences of the chromosomes.<ref>{{cite journal |last1=Hermsen |first1=J. G. Th. |last2=Ramanna |first2=M. S. |title=Barriers to hybridisation of ''Solanum bulbocastanum'' Dun. and ''S. Verrucosum'' Schlechtd. and structural hybridity in their F1 plants |journal=Euphytica |volume=25 |number=1 |date=January 1976 |doi=10.1007/BF00041523 |pages=1–10|bibcode=1976Euphy..25....1H |s2cid=37518270}}</ref>

===Speciation===
[[File:Triticum durum.jpg|thumb|[[Durum]] wheat is [[tetraploid]], derived from [[wild emmer]] wheat, which is a hybrid of two diploid wild grasses, ''[[Triticum urartu]]'' and a wild goatgrass such as ''Aegilops searsii'' or ''[[Aegilops speltoides|Ae. speltoides]]''.<ref name="Gornicki">{{Cite journal |title=The chloroplast view of the evolution of polyploid wheat |last1=Gornicki |first1=Piotr |display-authors=etal |date=2014 |journal=New Phytologist |volume=204 |issue=3 |pages=704–714 |doi=10.1111/nph.12931|pmid=25059383|bibcode=2014NewPh.204..704G }}</ref>]]
{{Main|Hybrid speciation|Hybrid zone}}

A few animal species are the result of hybridization. The [[Lonicera fly]] is a natural hybrid. The American [[red wolf]] appears to be a hybrid of the [[gray wolf]] and the [[coyote]],<ref>{{cite news |last=Esch |first=Mary |title=Study: Eastern wolves are hybrids with coyotes |url= http://archive.boston.com/news/science/articles/2011/05/31/study_eastern_wolves_are_hybrids_with_coyotes/ |work=Boston.com |agency=Associated Press |date=31 May 2011 |access-date=22 March 2017 |archive-date=22 March 2017 |archive-url= https://web.archive.org/web/20170322095126/http://archive.boston.com/news/science/articles/2011/05/31/study_eastern_wolves_are_hybrids_with_coyotes/ |url-status=live}}</ref> although its taxonomic status has been a subject of controversy.<ref>{{cite journal |title=Conservation genomics in perspective: A holistic approach to understanding Canis evolution in North America |journal=Biological Conservation |volume=155 |date=2012 |pages=186–192 |url= http://people.trentu.ca/brentpatterson/index_files/Rutledge%20et%20al%202012%20-%20conservation%20genomics%20in%20perspective.pdf |archive-url= https://ghostarchive.org/archive/20221009/http://people.trentu.ca/brentpatterson/index_files/Rutledge%20et%20al%202012%20-%20conservation%20genomics%20in%20perspective.pdf |archive-date=9 October 2022 |url-status=live |doi=10.1016/j.biocon.2012.05.017 |last1=Rutledge |first1=Linda Y. |bibcode=2012BCons.155..186R |display-authors=etal}}{{Dead link|date=January 2020 |bot=InternetArchiveBot |fix-attempted=yes}}</ref><ref>{{cite journal |title=An account of the taxonomy of North American wolves from morphological and genetic analyses |date=2012 |journal=North American Fauna |volume=77 |pages=1–67 |doi=10.3996/nafa.77.0001 |last1=Chambers |first1=Steven M. |display-authors=etal |url= https://digital.library.unt.edu/ark:/67531/metadc700981/ |doi-access=free}}</ref><ref>{{cite web |last=Dumbacher |first=J. |url= http://www.fws.gov/home/wolfrecovery/pdf/Final_Review_of_Proposed_rule_regarding_wolves2014.pdf |title=Review of Proposed Rule Regarding Status of the Wolf Under the Endangered Species Act |archive-url= https://web.archive.org/web/20140611123034/http://www.fws.gov/home/wolfrecovery/pdf/Final_Review_of_Proposed_rule_regarding_wolves2014.pdf |archive-date=11 June 2014 |work=FWS.gov |publisher=NCEAS |date=January 2014}}</ref> The European [[edible frog]] is a semi-permanent hybrid between [[pool frog]]s and [[marsh frog]]s; its population requires the continued presence of at least one of the parent species.<ref>{{cite journal |last1=Frost |first1=Grant |display-authors=etal |title=The amphibian tree of life |journal=Bulletin of the American Museum of Natural History |issue=297 |date=15 March 2006 |volume=297 |pages=1–291 |doi=10.1206/0003-0090(2006)297[0001:TATOL]2.0.CO;2 |s2cid=86140137 |doi-access=free}}</ref> Cave paintings indicate that the [[European bison]] is a natural hybrid of the [[aurochs]] and the [[steppe bison]].<ref>{{Cite journal |last1=Soubrier |first1=Julien |display-authors=etal |date=18 October 2016 |title=Early cave art and ancient DNA record the origin of European bison |journal=Nature Communications |volume=7 |doi=10.1038/ncomms13158 |pages=13158 |pmid=27754477 |pmc=5071849|bibcode=2016NatCo...713158S}}</ref><ref>{{Cite news |url= http://www.smithsonianmag.com/smart-news/how-cave-art-helped-dig-new-animal-species-180960833/?no-ist |title=Cave Paintings Help Unravel the Mystery of the 'Higgs Bison' |last=Daley |first=Jason |newspaper=Smithsonian |access-date=20 October 2016 |archive-date=21 October 2016 |archive-url= https://web.archive.org/web/20161021130804/http://www.smithsonianmag.com/smart-news/how-cave-art-helped-dig-new-animal-species-180960833/?no-ist |url-status=live}}</ref>

[[Plant]] hybridization is more commonplace compared to animal hybridization. Many [[crop]] species are hybrids, including notably the polyploid [[wheat]]s: some have four sets of chromosomes (tetraploid) or six (hexaploid), while other wheat species have (like most [[eukaryotic]] organisms) two sets ([[diploid]]), so hybridization events likely involved the doubling of chromosome sets, causing immediate genetic isolation.<ref>{{cite book |last=Hancock |first=James F. |date=2004 |title=Plant Evolution and the Origin of Crop Species |publisher=CABI Publishing |isbn=9780851996851 |url= https://archive.org/details/plantevolutionor0000hanc}}</ref>

Hybridization may be important in speciation in some plant groups. However, homoploid hybrid speciation (not increasing the number of sets of chromosomes) may be rare: by 1997, only eight natural examples had been fully described. Experimental studies suggest that hybridization offers a rapid route to speciation, a prediction confirmed by the fact that early generation hybrids and ancient hybrid species have matching genomes, meaning that once hybridization has occurred, the new [[Eukaryote hybrid genome|hybrid genome]] can remain stable.<ref>{{Cite journal |last=Rieseberg |first=Loren H. |title=Hybrid Origins of Plant Species |journal=Annual Review of Ecology, Evolution, and Systematics |date=1997 |volume=28 |issue=1 |pages=359–389 |doi=10.1146/annurev.ecolsys.28.1.359 |bibcode=1997AnRES..28..359R |citeseerx=10.1.1.718.9871}}</ref>

Many [[hybrid zone]]s are known where the ranges of two species meet, and hybrids are continually produced in great numbers. These hybrid zones are useful as biological model systems for studying the mechanisms of speciation. Recently DNA analysis of a bear shot by a hunter in the [[Northwest Territories]] confirmed the existence of naturally occurring and fertile [[grizzly–polar bear hybrid]]s.<ref>{{cite news |title=Hybrid bear shot dead in Canada |url= http://news.bbc.co.uk/2/hi/science/nature/4766217.stm |work=BBC News |date=13 May 2006 |access-date=10 June 2006 |archive-date=22 June 2006 |archive-url= https://web.archive.org/web/20060622014402/http://news.bbc.co.uk/2/hi/science/nature/4766217.stm |url-status=live}}</ref>

===Hybrid vigour===
[[File:Salvia jurisicii x nutans - Flickr - peganum.jpg|thumb|[[Heterosis|Hybrid vigour]]: ''Salvia jurisicii x nutans'' hybrids (top centre, with flowers) are taller than their parents ''[[Salvia jurisicii]]'' (centre tray) or ''[[Salvia nutans]]'' (top left).]]
{{Main|Heterosis}}

Hybridization between reproductively isolated species often results in hybrid offspring with lower fitness than either parental. However, hybrids are not, as might be expected, always intermediate between their parents (as if there were blending inheritance), but are sometimes stronger or perform better than either parental lineage or variety, a phenomenon called [[heterosis|heterosis, hybrid vigour, or heterozygote advantage]]. This is most common with plant hybrids.<ref>{{cite journal |title=Evaluating the utility of Arabidopsis thaliana as a model for understanding heterosis in hybrid crops |journal=Euphytica |volume=156 |issue=1–2 |date=July 2007 |doi=10.1007/s10681-007-9362-1 |pages=157–171 |last=Stokes |first=David |bibcode=2007Euphy.156..157S |s2cid=22964055}}</ref> A [[Transgressive segregation|transgressive phenotype]] is a phenotype that displays more extreme characteristics than either of the parent lines.<ref>{{cite journal |title=Transgressive segregation, adaptation and speciation |journal=Heredity |date=July 1999 |first1=Loren H. |last1=Rieseberg |pmid=10583537 |first2=Margaret A. |last2=Archer |first3=Robert K. |last3=Wayne |volume=83 |issue=4 |pages=363–372 |doi=10.1038/sj.hdy.6886170|s2cid=2651616 |doi-access=free|bibcode=1999Hered..83..363R }}</ref> [[Plant breeding|Plant breeders]] use several techniques to produce hybrids, including line breeding and the formation of complex hybrids. An economically important example is hybrid [[maize]] (corn), which provides a considerable seed yield advantage over open pollinated varieties. [[Hybrid seed]] dominates the commercial maize seed market in the United States, Canada and many other major maize-producing countries.<ref>{{cite book |last=Smith |first=C. Wayne |title=Corn: Origin, History, Technology, and Production |publisher=Wiley |date=2004 |page=332}}</ref>

In a hybrid, any trait that falls outside the range of parental variation (and is thus not simply intermediate between its parents) is considered heterotic. ''Positive heterosis'' produces more robust hybrids, they might be stronger or bigger; while the term ''negative heterosis'' refers to weaker or smaller hybrids.<ref>{{cite book |last=McCarthy |first=Eugene M. |date=2006 |title=Handbook of Avian Hybrids of the World |publisher=Oxford University Press |page=17 |isbn=9780195183238}}</ref> Heterosis is common in both animal and plant hybrids. For example, hybrids between a lion and a tigress ("[[ligers]]") are much larger than either of the two progenitors, while "[[tigons]]" (lioness × tiger) are smaller. Similarly, the hybrids between the common pheasant (''[[Phasianus colchicus]]'') and domestic fowl (''[[Gallus gallus]]'') are larger than either of their parents, as are those produced between the common pheasant and hen golden pheasant (''[[Chrysolophus pictus]]'').<ref>{{cite book |last=Darwin |first=Charles |author-link=Charles Darwin |date=1868 |title=Variation of Animals and Plants under Domestication |volume=II |page=125}}</ref> Spurs are absent in hybrids of the former type, although present in both parents.<ref>{{cite journal |last=Spicer |first=J. W. G. |date=1854 |title=Note on hybrid gallinaceous birds |journal=The Zoologist |volume=12 |pages=4294–4296}}</ref>