How much DNA do brothers and sisters share? How much DNA do twins have in common? Can a pair of siblings have their DNA tested? In our latest expert article we tackle some frequently asked questions about siblings and DNA.

How much DNA do brothers and sisters share?

Brothers and sisters, known as siblings, have one or both parents in common. A full sibling has the same biological mother and father and is a first-degree relative. Full siblings, on average, share 50% of their DNA. Half-siblings share either a mother or a father. Half-siblings are second-degree relatives and have around 25% overlap in their human genetic variation. By comparison, Identical twins, which will be the same sex, share 100% of their DNA.

Sibling DNA testing can DNA test individuals to establish whether it is more likely that they share both parents, have one parent in common, or are unrelated

How does sibling DNA testing work?

A DNA sample needs to be collected from both siblings. This is a simple process and just involves rubbing the inside of their cheeks with a swab to collect cheek (buccal) cells. Full instructions on how to collect the samples are included in the testing kits.

The DNA is extracted from the cells when these swabs are returned to our Warrington-based laboratory. Our in-house DNA experts then use statistical analysis to evaluate the amount of DNA shared between the two siblings, and the frequency of the observed DNA within the relevant population. Up to 42 DNA markers are analysed. Full siblings are expected to have more DNA in common than half-siblings, and half-siblings normally share more DNA than unrelated individuals.

Guaranteed results or your money back

Paternity DNA testing and maternity DNA testing usually provide conclusive results. This is because it is possible to identify which half of the child’s DNA is inherited from the father and which half is from the mother. If a biological parent is undergoing DNA testing, both child and parent will share identical sections of DNA at each marker.

Sibling DNA tests are more complex. This means that you may not get a conclusive answer. Across the testing industry, sibling DNA testing can be up to 40% inconclusive. AlphaBiolabs has been able to reduce this inconclusive rate down to 24%. However, should you use our sibling DNA testing service and not get a conclusive result, we guarantee to refund the price of your sibling test.

Further details on AlphaBiolabs’ sibling testing and other DNA testing services can be found on our website. Alternatively, please call our Customer Services team on 01 402 9466 or email