Editing Gene flow (section)

=== Hybridization ===
In some instances, when a species has a sister species and breeding capabilities are possible due to the removal of previous barriers or through introduction due to human intervention, species can hybridize and exchange genes and corresponding traits.<ref>{{Cite journal|last=Mallet|first=James|date=2005|title=Hybridization as an invasion of the genome|journal=Trends in Ecology and Evolution|volume=20|issue=5|pages=229–237|doi=10.1016/j.tree.2005.02.010|pmid=16701374|bibcode=2005TEcoE..20..229M }}</ref> This exchange is not always clear-cut, for sometimes the hybrids may look identical to the original species [[Phenotype|phenotypically]] but upon testing the mtDNA it is apparent that hybridization has occurred. Differential hybridization also occurs because some traits and DNA are more readily exchanged than others, and this is a result of selective pressure or the absence thereof that allows for easier transaction. In instances in which the introduced species begins to replace the native species, the native species becomes threatened and the biodiversity is reduced, thus making this phenomenon negative rather than a positive case of gene flow that augments genetic diversity.<ref>{{cite journal| vauthors = Allendorf FW, Leary RF, Spruell P, Wenburg JK |date=2001-11-01|title=The problems with hybrids: setting conservation guidelines |journal=Trends in Ecology & Evolution |volume=16|issue=11|pages=613–622|doi=10.1016/S0169-5347(01)02290-X }}</ref> Introgression is the replacement of one species' alleles with that of the invader species. It is important to note that hybrids are sometime less "fit" than their parental generation,<ref>{{cite journal | vauthors = Steeves TE, Maloney RF, Hale ML, Tylianakis JM, Gemmell NJ | title = Genetic analyses reveal hybridization but no hybrid swarm in one of the world's rarest birds | journal = Molecular Ecology | volume = 19 | issue = 23 | pages = 5090–100 | date = December 2010 | pmid = 21050294 | doi = 10.1111/j.1365-294X.2010.04895.x | bibcode = 2010MolEc..19.5090S }}</ref> and as a result is a closely monitored genetic issue as the ultimate goal in conservation genetics is to maintain the genetic integrity of a species and preserve biodiversity.