Sibling DNA tests

Sibling DNA testing

Sibling DNA testing is used to determine whether two people have biological parents in common, when those parents are not available for testing.

Full siblings - Individuals are full siblings when both biological parents are the same

Half siblings - Half siblings share only one biological parent, either the mother or the father.

Sibling analysis is not as conclusive as paternity testing. The results will provide a statistical likelihood of whether two individuals are true biological relatives, but sibling analysis cannot provide a conclusive result.

If any of the parents of the siblings who are being assessed are available for testing, this will aid the analysis and may increase the certainty of the result. As in a paternity test a DNA profile is produced for each person made up of a number of DNA markers.  The DNA profiles of the two people are then compared. On average full siblings will share more DNA markers than half siblings, and half siblings share more DNA markers than unrelated people.  The statistical analysis performed will determine the most likely relationship given the DNA results.

Why are sibling tests not conclusive?

Although DNA testing is highly informative, this test involves assessing a relationship to another person (the alleged shared parent) without actually testing their DNA.  This can never be as conclusive as actually testing that alleged parent’s DNA.

Comparing DNA profiles can provide a strong indication of a sibling relationship.  However, it will not always reveal the true nature of the relationship because of the patterns of DNA inheritance.  It is possible, for example, for two individuals to have the same parents and only share a small number of their DNA markers.  A sibling test can therefore only conclude which is the most likely relationship given the DNA evidence.

Alternative testing

In some instances, where both siblings are male, testing using another type of DNA test called a Y-chromosome test may provide useful evidence of the relationship.  This type of test can confirm conclusively that two males do not share the same father.

Before proceeding with sibling testing it is recommended that you discuss the matter in detail with a DNA testing company who will be able to advise you who are the best people to test and which type of test is most likely to be of assistance to you.

For further information on the work of the Human Genetics Commission and the Human Tissue Act visit the HGC’s website www.hgc.gov.uk.

• What is DNA and why do we test it?

• What is DNA paternity testing?

• What does DNA paternity testing involve?

• Accreditation of testing laboratories

• Selecting a testing service - making an informed choice

• The Human Tissue Act

• DNA test results and reports

• Assessing DNA reports

• How much does it cost?

• DNA testing: Frequently asked questions

• Advice and support groups

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