Family

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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:

Kinship Degree of
relationship
Genetic
overlap
Inbred strain not applicable 99%
Identical twins not applicable 100%[1]
Full sibling first-degree 50% (2−2+2−2)
Parent-offspring[2] first-degree 50% (2−1)
Offspring/progeny first-degree 50% (2−1)
Half-sibling second-degree 25% (2−2)
3/4 siblings or sibling-cousin second-degree 37.5% (2−2+2⋅2−4)
Grandmother/grandfather second-degree 25% (2−2)
Niece/nephew third-degree 25% (2⋅2−3)
Aunt/uncle third-degree 25% (2⋅2−3)
Half-aunt, half-uncle third-degree 12.5% (2⋅2−4)
Half-niece/half-nephew 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)[3]

Notes:

  1. 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.
  2. "Kin Selection". Benjamin/Cummings. Retrieved 2007-11-25. 
  3. This degree of relationship is usually indistinguishable from the relationship to a random individual within the same population (tribe, country, ethnic group).

Related pages[change | change source]