Editing Inbreeding (section)

==Measures==
A measure of inbreeding of an individual A is the probability ''F''(A) that both alleles in one locus are derived from the same allele in an ancestor.  These two identical alleles that are both derived from a common ancestor are said to be [[identical by descent]]. This probability F(A) is called the "[[coefficient of inbreeding]]".<ref name=":0">{{cite journal | vauthors = Wright S | year = 1922 | title = Coefficients of inbreeding and relationship | url = https://zenodo.org/record/1431365| journal = American Naturalist | volume = 56 | issue = 645| pages = 330–338 | doi=10.1086/279872| bibcode = 1922ANat...56..330W | s2cid = 83865141 }}</ref>

Another useful measure that describes the extent to which two individuals are related (say individuals A and B) is their coancestry coefficient f(A,B), which gives the probability that one randomly selected allele from A and another randomly selected allele from B are identical by descent.<ref>{{cite journal | vauthors = Reynolds J, Weir BS, Cockerham CC | title = Estimation of the coancestry coefficient: basis for a short-term genetic distance | journal = Genetics | volume = 105 | issue = 3 | pages = 767–79 | date = November 1983 | doi = 10.1093/genetics/105.3.767 | pmid = 17246175 | pmc = 1202185 }}</ref> This is also denoted as the kinship coefficient between A and B.<ref>{{Cite journal| vauthors = Casas AM, Igartua E, Valles MP, Molina-Cano JL |date=November 1998|title=Genetic diversity of barley cultivars grown in Spain, estimated by RFLP, similarity and coancestry coefficients |journal=Plant Breeding |volume=117|issue=5|pages=429–35 |doi=10.1111/j.1439-0523.1998.tb01968.x |bibcode=1998PBree.117..429C |hdl=10261/121301}}</ref>

A particular case is the self-coancestry of individual A with itself, f(A,A), which is the probability that taking one random allele from A and then, independently and with replacement, another random allele also from A, both are identical by descent. Since they can be identical by descent by sampling the same allele or by sampling both alleles that happen to be identical by descent, we have f(A,A) = 1/2 + F(A)/2.<ref>{{cite book | vauthors = Malecot G | page = 1048 | title = Les Mathématiques de l'hérédité. | publisher = Masson et Cie | location = Paris }}</ref>

Both the inbreeding and the coancestry coefficients can be defined for specific individuals or as average population values. They can be computed from genealogies or estimated from the population size and its breeding properties, but all methods assume no selection and are limited to neutral alleles.

There are several methods to compute this percentage. The two main ways are the path method<ref>[http://www.braquedubourbonnais.info/en/inbreeding-calculation.htm How to compute and inbreeding coefficient (the path method)], Braque du Bourbonnais.</ref><ref name=":0" /> and the tabular method.<ref>{{cite web | first = Knud | last = Christensen | url = http://www.husdyr.kvl.dk/htm/kc/popgen/genetics/4/5.htm | title = 4.5 Calculation of inbreeding and relationship, the tabular method | work = Genetic calculation applets and other programs | publisher = Genetics pages | access-date = 2010-10-07 | archive-date = 2010-03-27 | archive-url = https://web.archive.org/web/20100327075815/http://www.husdyr.kvl.dk/htm/kc/popgen/genetics/4/5.htm | url-status = dead }}</ref><ref>{{Cite journal| vauthors = García-Cortés LA, Martínez-Ávila JC, Toro MA |date=2010-05-16|title=Fine decomposition of the inbreeding and the coancestry coefficients by using the tabular method |journal=Conservation Genetics |volume=11 |issue=5 |pages=1945–52 |doi=10.1007/s10592-010-0084-x |bibcode=2010ConG...11.1945G |s2cid=2636127}}</ref>

Typical coancestries between relatives are as follows:
* Father/daughter or mother/son → 25% ({{frac|1|4}})
* Brother/sister → 25% ({{frac|1|4}})
* Grandfather/granddaughter or grandmother/grandson → 12.5% ({{frac|1|8}})
* Half-brother/half-sister, Double cousins → 12.5% ({{frac|1|8}})
* Uncle/niece or aunt/nephew → 12.5% ({{frac|1|8}})
* Great-grandfather/great-granddaughter or great-grandmother/great-grandson → 6.25% ({{frac|1|16}})
* Half-uncle/niece or half-aunt/nephew → 6.25% ({{frac|1|16}})
* First cousins → 6.25% ({{frac|1|16}})