DNA Sibling Testing

DNA sibling testing is available for those who are interested in or have a need to determine sibling relationships. Sibling relationships include brother/sister, brother/brother, or sister/sister relationships. DNA sibling testing is more complex than simple paternity or maternity testing. Because of this complexity, the results of DNA sibling testing are not as definitive. Results normally consist of a siblingship “index” that will indicate the genetic odds in favor of (or against) a sibling relationship.

Most DNA labs will only test two siblings at a time. DNA samples are required from both siblings. DNA sibling testing is more accurate when the DNA sample of at least one parent is provided. For this reason, the parent’s DNA sample is highly recommended, but is not required.

The preferred parent DNA sample is the mother’s DNA. When the alleged siblings’ mother (or mothers) participates in the test, the mother’s contribution to the siblings’ genetic profiles can be eliminated, and the lab can concentrate on the father’s contribution. “Motherless” DNA sibling testing often requires additional time for analysis and may cost more. Sample collection for DNA sibling testing is accomplished in the same way as most DNA testing–through the use of buccal swabs rubbed against the inside of the mouth to collect loose cheek cells.
Two types of DNA sibling testing is available. The half siblingship test is performed when the alleged siblings know that they do not have the same biological mother, and would like to find out if they have the same biological father. The full siblingship test comes into play when two alleged siblings have the same biological mother and would like to determine if they also have the same biological father. Full siblings have fifty percent of their DNA in common, while half siblings have twenty-five percent of their DNA in common.

There are actually not very many cases in which DNA sibling testing is utilized in legal proceeding. Most DNA sibling testing is done for peace of mind or to satisfy curiosity. But legally admissible DNA sibling testing is available from most online providers.

DNA sibling testing for peace of mind can be accomplished using a home collection kit. The tested parties can collect their own DNA samples and return them to the lab. Legally admissible DNA sibling testing requires that DNA samples be collected by a neutral third party. Third-party collection ensures that chain of custody is preserved, making the DNA sibling test results admissible in court. DNA sibling testing usually takes from two to three weeks to complete.