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A family is a group of people related by blood or by birth.
Closeness[change | change source]
Some family members are genetically closer to each other. The following table gives examples:
|Inbred strain||not applicable||99%|
|Identical twins||not applicable||100%|
|Full sibling||first-degree||50% (2−2+2−2)|
|3/4 siblings or sibling-cousin||second-degree||37.5% (2−2+2⋅2−4)|
|Half-aunt, half-uncle||third-degree||12.5% (2⋅2−4)|
|Great grandparent||third-degree||12.5% (2−3)|
|First cousin||fourth-degree||12.5% (2⋅2−4)|
|Double first couisin||fourth-degree||25% (2−3+2−3)|
|Half-first cousin||fourth-degree||6.25% (2−4)|
|First cousin once removed||fifth-degree||6.25% (2⋅2−5)|
|Second cousin||sixth-degree||3.125% 3.13% (2−6+2−6)|
|Double second cousin||sixth-degree||6.25% (4⋅2−6)|
|Triple second cousin||sixth-degree||12.5% (8⋅2−6)|
|Quadruple second cousin||sixth-degree||9.38% (6⋅2−6)|
|Third cousin||seventh-degree||0.781% (2⋅2−8)|
|Fourth cousin||tenth-degree||0.20% (2⋅2−10)|
- By replacement in the definition of the notion of "generation" by meiosis". Since identical twins are not separated by meiosis, there are no "generations" between them, hence n=0 and r=1. See genetic-genealogy.co.uk.
- "Kin Selection". Benjamin/Cummings. Retrieved 2007-11-25.
- This degree of relationship is usually indistinguishable from the relationship to a random individual within the same population (tribe, country, ethnic group).