DNA siblingship tests determine the statistical probability of whether siblings (brothers and sisters) share the same two parents or not. The cost of the DNA testing service includes two siblings, but you may add more as needed; for instance a third sibling.
When the issue of siblingship is in question, the recommended method to determine whether individuals are true biological siblings is to test their parents. In situations where the alleged parents are unavailable for testing, a DNA siblingship test can be performed to analyze the relationship of biological siblings.
Including one common parent greatly increases the accuracy of this type of analysis and is recommended if at all possible. If this is not possible, disclosing that siblings share a common mother or father can also lead to more meaningful results.
Unlike a paternity test which will always provide a conclusive result, siblingship tests are different. When a siblingship test is conducted, the DNA laboratory will determine the genetic profile of the alleged siblings. Based on the type of genetic material inherited by each sibling, a siblingship DNA index is determined. If the siblingship DNA index is less than 1.00, this indicates non-relatedness. If the siblingship DNA index is greater than 1.00, this indicates that the two tested individuals are more likely to be true biological siblings. The higher the value of the siblingship DNA index, the greater the likelihood that the two individuals are true biological siblings. To analyze the possibility that the siblings share only one common parent versus two common parents (mother and father), a half siblingship DNA index is obtained. The ratio of the half siblingship DNA index versus the full siblingship DNA index would provide you with an idea of whether the two individuals are more likely to share only one common parent (e.g. mother only) or two common parents (mother and alleged father).
Our siblingship tests are preformed using what's known as an "All-vs-All" methodology. For example, if you have two siblings, Alice and Bob, one report will be generated which details the relationship between Alice and Bob. With three siblings you would receive 3 reports which describe the relationships between: Alice & Bob, Alice & Charlie and Bob & Charlie. Four siblings would yield 6 reports: Alice & Bob, Alice & Charlie, Alice & David, Bob & Charlie, Bob & David, and Charlie & David. The amount of reports would subsequently grow exponentially. If you have any questions regarding these reports, please feel free to contact us.
Please note: In some cases, a Y-STR DNA Test can provide more conclusive results for males determining common paternal lineage. If siblings are trying to determine whether or not they share the same maternal lineage, an X-SV DNA Test may be the analysis of choice.