Biology:Kinship coefficient
The kinship coefficient is a simple measure of relatedness, defined as the probability that a pair of randomly sampled homologous alleles are identical by descent.[1] More simply, it is the probability that an allele selected randomly from an individual, i, and an allele selected at the same autosomal locus from another individual, j, are identical and from the same ancestor.
The Kinship Coefficient
The kinship coefficient between two individuals, i and j, is represented as Φij. The kinship coefficient between a non-inbred individual and itself, Φii, is equal to 1/2. This is due to the fact that humans are diploid, meaning the only way for the randomly chosen alleles to be identical by descent is if the same allele is chosen twice(probability 1/2). Similarly, the relationship between a parent and a child is found by the chance that the randomly picked allele in the child is from the parent (probability 1/2) and the probability of the allele that is picked from the parent being the same one passed to the child (probability 1/2). Since these two events are independent of each other, they are multiplied Φij = 1/2 X 1/2 = 1/4.[2][3] The coefficient of relatedness is equal to twice the kinship coefficient.
| Relationship | Kinship Coefficient |
|---|---|
| Individual-self | 1/2 |
| Siblings | 1/4 |
| Parent-offspring | 1/4 |
| Grandparent-grandchild | 1/8 |
| Uncle/aunt-nephew/niece | 1/8 |
| First Cousins | 1/16 |
| Half-siblings | 1/8 |
Several of the most common family relationships and their corresponding kinship coefficient.
References
Bibliography
Lange, Kenneth. Mathematical and statistical methods for genetic analysis. Springer, 2003.
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