Table 1.
Familial Relationship | IBD0 | IBD1 | IBD2 |
---|---|---|---|
Parental | 0 | 1 | 0 |
Full-sibling | 0.25 | 0.5 | 0.25 |
Half-sibling, avuncular, and grandparental | 0.5 | 0.5 | 0 |
First-cousin, great-grandparental, great-avuncular, and half-avuncular | 0.75 | 0.25 | 0 |
Distantly related | varies | varies | 0 |
Unrelated (includes relationships beyond the third degree) | 1 | 0 | 0 |
IBD0, IBD1, and IBD2 are the genome proportions shared on 0, 1, and 2 chromosomes, respectively, between two individuals. Many relationships share the same expected mean IBD proportions; however, for full-sibling, second-degree, and third-degree relationships, a variance around the expected mean is due to the random nature of recombination events. Genotyping and other technical errors can contribute to this variance.