View source for Outcrossing

{{short description|Technique of crossing between different breeds}}
{{about|the technique used in animal and plant breeding|naturally occurring outcrossing|Allogamy}}
'''Out-crossing''' or '''out-breeding''' is the technique of crossing between different breeds. This is the practice of introducing distantly related genetic material into a breeding line, thereby increasing [[genetic diversity]].
== Outcrossing in animals ==
Outcrossing can be a useful technique in [[Animal husbandry|animal breeding]]. The outcrossing breeder intends to remove the traits by using "new blood." With dominant traits, one can still see the expression of the traits and can remove those traits, whether one outcrosses, line breeds or inbreeds. With recessive traits, outcrossing allows for the recessive traits to migrate across a population. Many traits are Mendelian and therefore exhibit a more complicated intermediate phenotype. The outcrossing breeder then may have individuals that have many [[Deleterious mutation|deleterious]] genes that may be expressed by subsequent inbreeding. There is now a gamut of deleterious genes within each individual in many dog breeds.<ref name="Downside">{{cite web|last=Sharp|first=C.A.|url=http://www.canine-genetics.com/Price.htm|title=The Downside of Inbreeding: It's Time For a New Approach|website=Canine-Genetics.com|date=26 February 1999|publisher=Double Helix Network News Vol. VII, No. 1 (Winter 1999)|archive-url=https://web.archive.org/web/20120126062039/http://www.canine-genetics.com/Price.htm|archive-date=26 January 2012}}</ref>
Increasing the variation of genes or alleles within the gene pool may protect against extinction by stressors from the environment among inbred animal populations. For example, in this context, a 2009 veterinary medicine study tried to determine the genetic diversity within cat breeds.<ref>{{cite web | url=http://www.vgl.ucdavis.edu/lyons/index.php | title=Feline Genetics | publisher=UC Davis Veterinary Genetics Laboratory | archive-url=https://web.archive.org/web/20090312020128/http://www.vgl.ucdavis.edu/lyons/index.php | archive-date=2009-03-12}}</ref>
A degree of outcrossing to avoid mating between very close relatives is believed to happen in the wild.<ref name="Downside"/>
== Outcrossing in plants and fungi ==
Outcrossing in plants is usually enforced by [[self-incompatibility]]. The primary adaptive function of [[flower]]s is the facilitation of outcrossing, a process that allows the masking of deleterious [[mutation]]s in the [[genome]] of progeny. The masking effect of outcrossing is known as [[complementation (genetics)|genetic complementation]],<ref>Bernstein H, Byerly HC, Hopf FA, Michod RE. Genetic damage, mutation, and the evolution of sex. Science. 1985 Sep 20;229(4719):1277-81. doi: 10.1126/science.3898363. PMID 3898363</ref> an effect also recognized as [[hybrid vigour|hybrid vigor]] or [[heterosis]]. Once outcrossing is established in a lineage of flowering plants due to the benefit of genetic complementation, subsequent switching to inbreeding becomes disadvantageous because it allows expression of the previously masked deleterious recessive mutations, i.e. [[inbreeding depression]].
Outcrossing in fungi involves [[syngamy]] between haploid cells produced by separate diploid individuals.<ref>{{cite journal |last1=Billiard |first1=S. |last2=López-Villavicencio |first2=M. |last3=Hood |first3=M. E. |last4=Giraud |first4=T. |title=Sex, outcrossing and mating types: unsolved questions in fungi and beyond |year=2012 |journal=Journal of Evolutionary Biology|volume=25 |issue=6 |pages=1020–1038 |doi=10.1111/j.1420-9101.2012.02495.x |pmid=22515640 |s2cid=25007801 |doi-access=free }}</ref>
Life-history traits are said to increase the probability of outcrossing in fungi, such as long-distance dispersal and persistence of the haploid stage. Some studies even show that fungi favor outcrossing in comparison to other mating types. In a study performed with the commercial button mushroom, ''Agaricus bisporus'', outcrossed populations of the fungi showed higher fitness than inbred ones in several fitness components.<ref>{{cite journal |last1=Xu |first1=J. |title=Analysis of inbreeding depression in Agaricus bisporus |year=1995 |volume=141 |issue=1 |pages=137–145 |journal=Genetics|doi=10.1093/genetics/141.1.137 |pmid=8536962 |pmc=1206712 }}</ref>
== General practice ==
Breeders [[inbreeding|inbreed]] within their genetic pool, attempting to maintain desirable traits and to [[cull]] those traits that are undesirable. When undesirable traits begin to appear, mates are selected to determine if a trait is recessive or dominant. Removal of the trait is accomplished by breeding two individuals known not to carry it.<ref>{{cite web|url=http://doublehelixranch.com/defects.html|title=Inbreeding, Linebreeding, and Outcrossing in Texas Longhorns|author=David M. Hillis|publisher=University of Texas at Austin}}</ref>
[[Gregor Mendel]] used outcrossing in his experiments with flowers. He then used the resulting offspring to chart inheritance patterns, using the crossing of siblings, and [[backcrossing]] to parents to determine how inheritance functioned.<ref name=autogenerated1>{{cite web|url=http://www.mendelweb.org/Mendel.html|title=Mendel's Paper (English - Annotated)|website=www.mendelweb.org}}</ref>
== Darwin's perspective ==
[[Charles Darwin]], in his book ''The Effects of Cross and Self-Fertilization in the Vegetable Kingdom,''.<ref>{{Cite web|url=http://darwin-online.org.uk/converted/published/1881_Worms_F1357/1876_CrossandSelfFertilisation_F1249/1876_CrossandSelfFertilisation_F1249.html|title=Darwin, C. R. 1876. The effects of cross and self fertilisation in the vegetable kingdom. London: John Murray.|website=darwin-online.org.uk}}</ref>{{rp|462}} stated regarding outcrossing that "the offspring from the union of two distinct individuals, especially if their progenitors have been subjected to very different conditions, have an immense advantage in height, weight, constitutional vigor and fertility over the self-fertilizing offspring from either one of the same parents". He thought that this observation was amply sufficient to account for outcrossing [[sexual reproduction]]. The disadvantages of self-fertilized offspring ([[inbreeding depression]]) are now thought to be largely due to the homozygous expression of deleterious recessive mutations;<ref name="pmid3324702">{{cite book |vauthors=Bernstein H, Hopf FA, Michod RE |chapter=The Molecular Basis of the Evolution of Sex |title=Molecular Genetics of Development |series=Advances in Genetics |volume=24 |pages=323–70 |year=1987 |pmid=3324702 |doi= 10.1016/s0065-2660(08)60012-7|isbn=9780120176243 }}</ref> and the fitness advantages of some outcrossed offspring are thought to be largely due to the heterozygous masking of such deleterious mutations except when such mutations lead to [[outbreeding depression]].
==See also==
*[[Consanguinity]]
*[[Heterosis]]
*[[Outbreeding depression]]
==References==
{{reflist}}
[[Category:Breeding]]
[[Category:Dog breeding]]
[[Category:Plant sexuality]]