By Casey Randall, Director of Genetics Laboratory at AlphaBiolabs
Last reviewed: 09/03/2026
š§ Listen to this article
A sibling DNA test can be used to prove whether individuals are half-siblings.
Half-siblings share one biological parent – the mother or father – and will normally share more DNA than people who are not related. This makes it possible to use sibling DNA testing to determine whether individuals are more likely to share one common parent, or more likely to be unrelated.
In this article, we discuss DNA testing for siblings in more detail.
Table of contents
What is sibling DNA testing?
A sibling DNA test is a type of DNA test that is used to determine whether two or more individuals are full siblings or half siblings.
For a sibling DNA test, cheek swabs are used to collect DNA samples from each sibling. For the most conclusive result, the laboratory will also request that the biological motherās DNA sample be submitted for testing, if possible.
Expert geneticists will then analyze and compare the DNA samples to determine the genetic profile of the possible siblings and calculate a sibling DNA index or likelihood ratio.
- A likelihood of greater than 10 supports that the tested individuals are likely to be related
- A likelihood of less than 0.1 is not supportive, meaning the individuals are unlikely to be related
- A likelihood which falls between 0.1 and 10 is considered inconclusive, which means a relationship cannot be determined based on the statistical probability obtained from the analysis
How much DNA do half-siblings share?
Half siblings share approximately 25% of their DNA, inheriting DNA in common from their shared parent (mother or father).
Male half-siblings who have the same biological father will have the same Y chromosome. This is because all male children inherit their Y chromosome from their father.
Can a sibling DNA test prove half-siblings?
Yes, a sibling DNA test can be used to prove whether individuals are half-siblings.
Half siblings share one biological parent ā the mother or father ā and will normally share more DNA than people who are not related.
This means that it is possible to use sibling DNA testing to determine whether individuals are:
- more likely to share one common parent i.e. they are half siblings, with one biological parent (mother or father) in common, or
- are more likely to be unrelated
Where can I buy a sibling DNA test?
Itās easy to order your peace of mind Sibling DNA Test online now for $149, with results emailed to you in 3 business days. The cost of the test includes your test kit and all lab fees.
Simply place your order online and we will ship your test kit out to you in discreet, plain packaging, for full confidentiality.
Your home test kit will contain everything you need to collect your samples and return them to our accredited laboratory for analysis by our expert geneticists.
Still have questions? Email our friendly Customer Services team at info@alphabiolabsusa.com.
I have a question and wondering if maybe you could give some direction please. I have had cancer a couple of times and was given radiation and very strong chemo drugs for Non-Hodgkins T-Cell Lymphoma and Breast Cancer over the years. I hear this can change your DNA. I’m trying
to find out if I have half sibblings but hear the cheek swab wont work for me since the drugs I was on for the cancer. What are your thoughts?
Thanks
Some chemotherapy drugs can damage DNA but this should not affect a DNA relationship test. For your own peace of mind, you can either carry out a single profile test to ensure we can obtain a DNA profile from the sample you provide, or we can carry out a comparison with a known relative (e.g. parent) to confirm that your profile hasnāt been affected and is suitable to perform a half sibling DNA test. If you have any more questions, please feel free to contact us on info@alphabiolabsusa.com or 727-325-2902.