| DNA Testing for Relationship > Kinship > Siblingship |
DNA Siblingship Test
| Full siblings Half siblings Twins |
- same biological father and biological mother - same biological father but different biological mother same biological mother but different father - identical twins and fraternal twins |
Tests to find out the paternity and/or maternity of 2 persons, full or half siblings |
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Interpretation of siblingship test results, full sib, half sib or unrelated? |
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| Combined Siblingship Index | Probability, W% | Likelihood Description, for Full & Half Siblingship |
| ≥ 20 | ≥ 95% | Most likely are siblings |
| 2 - 19 | 50 - 90% | Likely, but inconclusive Testing at least one of the parents and/or other relatives are highly encouraged; additional genetic analyses are also desirable |
| ≤ 1 | ≤50% | Exclusion |
| Sibling analysis is not as conclusive as paternity testing. The results will provide a probability that two individuals are biologically related, but it cannot provide a yes/no answer. On average full siblings will share more genetic markers than half siblings, and half siblings share more genetic markers than unrelated persons. |
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Siblingship Test Extended Info |
| Analyses of our cases involving siblings show that the calculated Combined Siblingship Indices (CSI)(Probabilities) of full siblings, half siblings and unrelated individuals sometimes overlap, resulting in uncertainty of the relationship. (JWL 2016, GenePro) |
| Range, CSI | Range, Probability | Median CSI | Probability | |
| Full siblings | 0.01 – 1,000,000,000 | 0.01% to ≥99.9999% | 10,000 | 99% |
| Half Siblings | 0.001 – 60,000 | 0.001% to 99.99% | 12 | 92% |
| Unrelated | 0.0005 - 15 | 0.0005% to 93% | 0.15 | 13% |
| If based on the CSI alone, full siblings could be interpreted as half siblings or even unrelated, and vice versa. Similar observation was reported in the AABB Annual Report, 2010. |
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To make the sibling-ship test more definitive: |
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| In cases where a standard marker panel does not yield an unequivocal result, the current trend is extended testing - | ||
| a. | Two alleged siblings + 1 or both grandparents |
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| b. | Two alleged siblings + other siblings and/or blood relatives | |
| c. | A mother or both mothers if are available should be tested; | |
| d. | Use more genetic markers on different chromosomes; | |
| e. | If the siblings are male, the Y-chromosome can be tested to determine if they have the same paternal lineage. | |
| Otherwise, other evidence (such as documents, eye witnesses) must be used to support a relationship whenever a low sibling index is obtained. | ||
