What Is a Siblingship Test?

Advancements in DNA testing have made it possible for individuals to obtain some forms of testing for an extremely reasonable price with kits used at home and mailed into a lab. Depending on the source administering the test, the rigor of the test, and special criteria such as whether the results should be court-admissible evidence, the costs for such tests range from as little as $100 up to a few hundred - still an extremely reasonable fee for the peace of mind such a test can provide.

What is a siblingship test?
Siblingship tests are one of the most common types of DNA testing. The goal is to determine to exactly what degree two people are related: whether they are full siblings (share both parents) or half-siblings (share one parent). Most of the time, half-sibling tests are done to determine if two individuals who know they share the same mother also share the same father. As the Internet and social media have greatly expanded the ability of potentially related individuals to find one another, this type of DNA testing is rapidly increasing in popularity.

How reliable are siblingship tests?
A great many factors go into the reliability of a siblingship test. A child and his or her parents share a number of direct markers that can more easily determine relationship. A maternity or paternity test, therefore, can more easily identify the parents of each potential sibling to find the ultimate answer to the sibling question - sometimes a company will label a siblingship test that nonetheless requires a sample from at least one parent.

A true siblingship test is often done when the parents are missing, deceased, or otherwise unwilling or unable to contribute genetic matter to a test, and requires only genetic material from the potential siblings in question. The genetic relationship between siblings - especially half-siblings - is significantly less direct than that of parent and child, so determining a relationship with certainty is not always guaranteed. Some pairs of siblings, by simple luck of the genetic draw, share more genetic markers than others. Sometimes the best that can be done is an indication that the two individuals are somehow related, without getting more specific.

What is done in a siblingship test?
To begin, a private DNA test is ordered from a company providing testing services. The kit contains simple mouth swabs that each individual uses, secures, and mails back to the lab for testing. The process takes only seconds. Results are usually available within one week of samples arriving back at the lab.

The lab identifies several sets of "short tandem repeat" (STR) markers in the DNA of each individual. These markers, which are short, repeating sections of DNA, are closely tied to parentage and are often used for all types of identification. Since siblings vary more than parents and children, these markers may or may not share much similarity between siblings. Once the genetic profiles are assembled, a statistic analysis is performed based on the similarity of the profiles, giving the odds that two individuals are related and how.

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