Types of families[change | change source]
Three types of family are: nuclear family, single-parent family and extended family.
A single-parent family is one where either the mother or father is caring for the children in the family.
(Both the "nuclear family" and the "single-parent family" are also called the "immediate family".)
Extended family means father, mother, daughters, sons, grandparents, uncles, aunts, cousins, nieces and nephews. In the United States, there are some circumstances where the extended family comes to live either with or in place of a member of the nuclear family. But in most cases in the United States the extended family no longer lives in the same place, but in many countries including China ,Pakistan and India, extended or joint families traditionally live together.
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. http://taumoda.com/web/PD/library/kin.html. 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).