Table of Genetic Relationship and Consanguinity

* It can be calculated that the proportion of genes shared by two relatives by descent from their most recent pair of common ancestors is (1/2)^(2g - 1), where g is the number of generations of descent and the symbol ‘^’ means ‘to the power of’. So this is the formula for r, a coefficient of relationship. For example, first cousins, descended from a pair of common grandparents (g = 2), will have (1/2)^(4 - 1) = 1/8 of their genes in common, and second cousins, descended from a pair of common great-grandparents (g = 3), will have (1/2)^(6 - 1) = 1/32 of their genes in common.
Degree Genetic relation Consanguinity
CoR No. of Genes Relation CoI No. of Genes
- 100% (1.0) 20,000 Identical twins
 
1st 50% (1/2) 10,000 Parents,
siblings,
children,
fraternal twins
25% (1/2 x 1/2 = 1/4) 5,000
 
2nd 25% (1/4) 5,000 Grandparents,
grandchildren,
aunts,
uncles,
nieces,
nephews,
half-siblings,
double-cousins (children of 2 siblings x 2 other siblings),
identical twin cousins (children of identical twins)
12.5% (1/2 x 1/4 = 1/8) 2,500
 
3nd 12.5% (1/8) 2,500 First cousins,
great grandparents,
great grandchildren,
great aunts,
great uncles,
grandnieces,
grandnephews,
half-aunts,
half-uncles,
half-nephews,
half-nieces
6.25% (1/2 x 1/8 = 1/16) 1,250
 
4th 6.25% (1/16) 1,250 Great great grandparents,
great great grandchildren,
great great aunts,
great great uncles,
great grandnieces,
great grandnephews,
first cousin once removed,
great half-aunts,
great half-uncles,
half-grandnephews,
half-grandnieces
3.13% (1/2 x 1/16 = 1/32) 625
 
5th 3.13% (1/32) 625 Great great great grandparents,
great great great grandchildren,
second cousins,
first cousin twice removed,
great great great uncles,
great great great aunts,
great great grandnieces,
great great grandnephews
great great half-aunts,
great great half-uncles,
great half-grandnephews,
great half-grandnieces
1.56% (1/2 x 1/32 = 1/64) 312.5
 
6th 1.56% (1/64) 312.5 Great great great great grandparents,
great great great great grandchildren,
second cousins once removed,
first cousin thrice removed,
great great great great uncles,
great great great great aunts,
great great great grandnieces,
great great great grandnephews
great great great half-aunts,
great great great half-uncles,
great great half-grandnephews,
great great half-grandnieces
0.78% (1/2 x 1/64 = 1/128) 156.25
 
7th 0.78% (1/128) 156.25 Great great great great great grandparents,
great great great great great grandchildren,
third cousins,
second cousins twice removed,
first cousin four times removed,
great great great great great uncles,
great great great great great aunts,
great great great great grandnieces,
great great great great grandnephews
great great great great half-aunts,
great great great great half-uncles,
great great great half-grandnephews,
great great great half-grandnieces
0.39% (1/2 x 1/128 = 1/256) 78.125

Sewall Wright, "Coefficients of Inbreeding and Relationship," The American Naturalist 56, no. 645 (Jul. - Aug., 1922): 330-338. DOI: 10.1086/279872.
https://www.journals.uchicago.edu/doi/10.1086/279872