Sibling tests can show if two people are biological siblings. Testing providers need a cheek swab sample from both ‘alleged’ siblings, these samples are then compared to see if there’s a genetic match.
There are a few different types of sibling test:
- ‘Full sibling’ tests are used when you want to find out if two siblings share both parents or just one.
- ‘Half sibling’ tests are used when you want to find out if two ‘alleged’ siblings have at least one parent in common.
These tests are sometimes used when an ‘alleged’ parent is not available for testing, and so a biological relationship with that parent can be proven by comparing the ‘alleged’ siblings instead.
On purchasing, the provider will send you a testing kit with everything you need to take the samples. You can take the samples at home and after you send the kit back, they’ll be in touch with the results a few days later. You can choose how you are contacted, with email generally being the quickest service. Some providers offer express services but these often come with extra fees.
Look out for companies selling cheap kits. That’s exactly what they are – just the kit and no testing. Providers then charge more to actually run the test when you return the samples.
’Peace of mind’ or ‘legal’ test?
There are two types of sibling test: ‘Peace of mind’ tests and ‘legal’ tests – legal tests are court admissible. The science behind the tests is exactly the same – the difference is that for court admissible tests, somebody official needs to watch them being taken so the court is assured that the samples came from the right people. Court admissible tests also require that the samples be handled securely all the way to the lab.
Are the tests accurate?
The tests are accurate, but not as accurate or as straightforward as paternity testing because siblings are less closely related to each other than to their parents. The tests compare DNA from both parties at certain ‘DNA locations’ to establish a genetic match. Most providers check 16 locations, some check up to 68 which improves the accuracy but which costs more.
If two siblings know they share one parent and are testing to see if they share two, many providers allow you to test the ‘known’ parent of both siblings as well for a more accurate result. This helps the provider to exclude 50% of the child’s DNA (the half which came from the known parent) so they can focus on establishing a match with the ‘alleged’ parent.
Different testing providers use different ways to express accuracy. Some will say they can test at a certain percentage accuracy, some will use a ‘relationship index’ where anything above ‘1.0’ indicates a biological relationship, and below ‘1.0’ indicates no biological relationship.
Testing male siblings for the same father- Y chromosome testing
If you’re testing male siblings for the same father, the test can be conducted with a greater degree of accuracy. Males have a Y chromosome that is passed from father to son, so if both males have the same Y chromosome, they share the same father.
What if the family members to be tested live far apart?
Some providers allow you to have the different parts of the test sent separately to those providing samples. All the kits are labelled so they can be matched back at the laboratory.
Watch out for shipping fees added at the checkout. Some providers with offices in the US will use labs overseas, so if having your samples tested in the US is important to you (and the provider’s website isn’t clear) check out our listings for these details.
