Editing Inbreeding (section)

===Domestic animals===
[[File:Shaded silver Persian Cat Missionhill Cosmic Rainstorm.jpg|thumb|right|Hereditary [[polycystic kidney disease]] is prevalent in the [[Persian cat]] breed, affecting almost half the population in some countries.<ref>{{Cite web|url=http://icatcare.org/advice/polycystic-kidney-disease|title=Polycystic kidney disease {{!}} International Cat Care|website=icatcare.org|access-date=2016-07-08}}</ref><ref>{{Cite web|url=http://www.vet.cornell.edu/fhc/Health_Information/PolycysticKidneyDisease.cfm|title=Polycystic Kidney Disease|website=www.vet.cornell.edu|access-date=2016-07-08}}</ref>]]

[[File:Intense inbreeding - Continuous sire to daughter mating.svg|thumb|right|An intensive form of inbreeding where an individual '''S''' is mated to his daughter '''D1''', granddaughter '''D2''' and so on, in order to maximise the percentage of '''S''''s genes in the offspring. 87.5% of '''D3''''s genes would come from '''S''', while '''D4''' would receive 93.75% of their genes from '''S'''.<ref name="TaveInbreeding">{{cite book| last = Tave | first = Douglas |title=Inbreeding and brood stock management|year=1999|publisher=Food and Agriculture Organization of the United Nations|isbn=978-92-5-104340-0|page=50|url=https://books.google.com/books?id=UdvIpkQOf5MC&pg=PA50}}</ref>]]

Breeding in domestic animals is primarily [[assortative mating|assortative]] breeding (see [[selective breeding]]). Without the sorting of individuals by trait, a breed could not be established, nor could poor genetic material be removed.
[[Homozygosity]] is the case where similar or identical alleles combine to express a trait that is not otherwise expressed (recessiveness). Inbreeding exposes recessive alleles through increasing homozygosity.<ref>{{Cite journal|title=Deleterious alleles in the context of domestication, inbreeding, and selection|year=2019|doi=10.1111/eva.12691|last1=Bosse|first1=Mirte|last2=Megens|first2=Hendrik-Jan|last3=Derks|first3=Martijn F. L.|last4=Cara|first4=Ángeles M. R.|last5=Groenen|first5=Martien A. M.|journal=Evolutionary Applications|volume=12|issue=1|pages=6–17|pmid=30622631|pmc=6304688|bibcode=2019EvApp..12....6B }}</ref>

Breeders must avoid breeding from individuals that demonstrate either homozygosity or heterozygosity for disease causing alleles.<ref>[http://extension.missouri.edu/publications/DisplayPub.aspx?P=G2036 G2036 Culling the Commercial Cow Herd: BIF Fact Sheet, MU Extension] {{Webarchive|url=https://web.archive.org/web/20160416142415/http://extension.missouri.edu/publications/DisplayPub.aspx?P=G2036 |date=2016-04-16 }}. Extension.missouri.edu. Retrieved on 2013-03-05.</ref> The goal of preventing the transfer of deleterious alleles may be achieved by reproductive isolation, [[Neutering|sterilization]], or, in the extreme case, [[culling]]. Culling is not strictly necessary if genetics are the only issue in hand. Small animals such as cats and dogs may be sterilized, but in the case of large agricultural animals, such as cattle, culling is usually the only economic option.

The issue of casual breeders who inbreed irresponsibly is discussed in the following quotation on cattle:
<blockquote>Meanwhile, milk production per cow per lactation increased from 17,444&nbsp;lbs to 25,013&nbsp;lbs from 1978 to 1998 for the Holstein breed. Mean breeding values for milk of Holstein cows increased by 4,829&nbsp;lbs during this period.<ref>{{cite web |title=Genetic Evaluation Results |url=http://aipl.arsusda.gov/main/data.html#gtrend
 |archive-url=https://web.archive.org/web/20010827074038/http://aipl.arsusda.gov/main/data.html
 |archive-date=August 27, 2001}}</ref> High producing cows are increasingly difficult to breed and are subject to higher health costs than cows of lower genetic merit for production (Cassell, 2001).

Intensive selection for higher yield has increased relationships among animals within breed and increased the rate of casual inbreeding.
Many of the traits that affect profitability in crosses of modern dairy breeds have not been studied in designed experiments. Indeed, all crossbreeding research involving North American breeds and strains is very dated (McAllister, 2001) if it exists at all.<ref>[http://www.nimss.umd.edu/homepages/home.cfm?trackID=2354 S1008: Genetic Selection and Crossbreeding to Enhance Reproduction and Survival of Dairy Cattle (S-284)] {{Webarchive|url=https://web.archive.org/web/20060910181548/http://nimss.umd.edu/homepages/home.cfm?trackID=2354 |date=2006-09-10 }}. Nimss.umd.edu. Retrieved on 2013-03-05.</ref></blockquote>

As a result of long-term cooperation between [[USDA]] and dairy farmers which led to a revolution in dairy cattle productivity, the United States has since 1992 been the world’s largest supplier of dairy bull semen.<ref name=USdairy>{{cite web |url=https://worksinprogress.co/issue/how-big-data-created-the-modern-dairy-cow/ |title=How big data created the modern dairy cow |date=December 5, 2024 |access-date=December 6, 2024 |first=Jared |last=Hutchens |work=Works In Progress |archive-url=https://archive.today/20241206185854/https://worksinprogress.co/issue/how-big-data-created-the-modern-dairy-cow/ |archive-date=December 6, 2024}}</ref>  However, US genomic technology has resulted in the US dairy cattle population becoming "the most inbred it’s ever been" and the rate of increase in US national milk yield has tapered off.  Efforts are now being made to identify desirable genes in cattle breeds not yet optimized by US dairy breeders in order to apply [[hybrid vigor]] to the US dairy cattle population and thus propel US dairy technology to even higher levels of productivity.

The BBC produced two documentaries on dog inbreeding titled ''[[Pedigree Dogs Exposed]]'' and ''[[Pedigree Dogs Exposed: Three Years On]]'' that document the negative health consequences of excessive inbreeding.

====Linebreeding====
Linebreeding is a form of inbreeding. There is no clear distinction between the two terms, but linebreeding may encompass crosses between individuals and their descendants or two cousins.<ref name="TaveInbreeding" /><ref name="UMissouri">{{cite web | last1 = Vogt | first1 = Dale | last2 = Swartz | first2 = Helen A. | last3 = Massey | first3 = John | title = Inbreeding: Its Meaning, Uses and Effects on Farm Animals | url = http://extension.missouri.edu/publications/DisplayPub.aspx?P=G2911 | work = MU Extension | publisher = [[University of Missouri]] | access-date = April 30, 2011 | date = October 1993 | archive-date = March 8, 2012 | archive-url = https://web.archive.org/web/20120308235825/http://extension.missouri.edu/publications/DisplayPub.aspx?P=G2911 | url-status = dead }}</ref> This method can be used to increase a particular animal's contribution to the population.<ref name="TaveInbreeding" /> While linebreeding is less likely to cause problems in the first generation than does inbreeding, over time, linebreeding can reduce the genetic diversity of a population and cause problems related to a too-small gene pool that may include an increased prevalence of genetic disorders and inbreeding depression.{{Citation needed|date=April 2011}}

====Outcrossing====
Outcrossing is where two unrelated individuals are crossed to produce progeny. In outcrossing, unless there is verifiable genetic information, one may find that all individuals are distantly related to an ancient progenitor. If the trait carries throughout a population, all individuals can have this trait. This is called the [[founder effect]]. In the well established breeds, that are commonly bred, a large gene pool is present. For example, in 2004, over 18,000 Persian cats were registered.<ref>[http://www.petplace.com/cats/top-cat-breeds-for-2004/page1.aspx Top Cat Breeds for 2004]. Petplace.com. Retrieved on 2013-03-05.</ref> A possibility exists for a complete outcross, if no barriers exist between the individuals to breed. However, it is not always the case, and a form of distant linebreeding occurs. Again it is up to the assortative breeder to know what sort of traits, both positive and negative, exist within the diversity of one breeding. This diversity of genetic expression, within even close relatives, increases the variability and diversity of viable stock.