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Main article: Coefficient of relationship
The inbreeding is computed as a percentage of chances for two alleles to be identical by descent. This percentage is called \"inbreeding coefficient\". There are several methods to compute this percentage, the two main ways are the path method[9] and the tabular method[10].[unreliable source?]
Typical inbreeding percentages are as follows:[dubious – discuss]
Father/daughter – mother/son – brother/sister → 25%
Half-brother/half-sister → 12.5%
Uncle/niece – aunt/nephew → 12.5%
Double first cousins → 12.5%
Half-uncle/niece → 6.25%
First cousins → 6.25%
First cousins once removed – half-first cousins → 3.125%
Second cousins – first cousins twice removed → 1.5625%
Second cousins once removed – half-second cousins → .78125%
An inbreeding calculation may be used to determine the general genetic distance among relatives by multiplying by 2, because any progeny would have a 1 in 2 risk of actually inheriting the identical alleles from both parents. For instance, the parent/child or sibling/sibling have 50% identical genetics. NOTE: For siblings, the degree of genetic relationship is not an automatic 50% (as it is with parents and their children), but a range from 100% at one extreme – as in the case of identical twins (who obviously could not mate as they are the same sex) – to an exceedingly unlikely 0%. Siblings share an average of 50% of their genes, but unlike the 50% ratio between parents and children, the actual ratio between siblings in any given case can vary.
