Editing Hybrid (biology) (section)

===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>