Half Sibling DNA Testing Accuracy

Are half-sibling DNA tests accurate?

This is a good question that is asked by many people. However, the real question is not how accurate are they but, How good is the prediction of half-siblingship?

The laboratory work is accurate – there are many quality control steps in the process of obtaining a DNA profile and from family studies/paternity samples there should never be an issue of generating a good profile (there are exceptions when the swabs are stored wet or similar mistakes),. but the vast majority of profiles are very accurate.

The issue is the statistical power of the method when trying to determine siblingship – full or half. That is not nearly as powerful as a direct comparison (common parent and child). Which may lead to an inclusive result, but still accurate. Of course, as stated earlier. If there is a common parent, the issue is solved, but without a common parent, labs have to rely on the DNA profile comparison and the number of shared genetic markers between the tested individuals.

Yes. The laboratory’s process is accurate but, the further away you get from direct comparisons (common parent and child) and move towards tests like (sibling and sibling). Sometimes may lead to a result being inclusive but the process of testing is accurate. Learn more about sibling DNA testing here.

There are several layers in answering this question. Ancestry testing companies use a different technique to examine a different genetic marker that is used for forensic or paternity testing. They use what is called a single nucleotide polymorphism (SNP – pronounced SNIP) – these are single base pair changes in the DNA sequence – we have lots and lots of lots of SNPs in our DNA. SNPs have been widely studied and are used in many genetic studies.

Relationship testing laboratories use a different genetic marker, short tandem repeats (STRs) – this kind of marker is used for paternity and forensic DNA.

Ancestry testing companies have several types of data they report – because they have a large database of SNPs and a large database of individuals who have been tested, they can ‘align’ the SNP data obtained from a client to their database and try to make sense of this comparison.

Another aspect of having the large SNP map and the database of several million individuals is that they have organized these into ‘family trees’ – what they consider related by the SNP maps they have generated – so in this way someone can ‘find’ their family tree and the claim is that they must be related, in some way, to this tree as their SNP map provides the link.

It is possible that the relationship claimed, sibling, is correct – however, there are large gaps in what we would need to know: do all of the SNPs get used for the family tree approach? How accurate are the SNP maps? Has any of the supposed matches been confirmed by more traditional STR testing? What quality control measures do Ancestry DNA testing companies take?

It is important to note, It’s possible to use SNPs as a marker for paternity testing and this has been demonstrated – you need several hundred (500 maybe) well-characterized SNP markers to arrive at decent statistics. The issue is that there will always be a few SNPs that do not match. .this is because of the mutation rate of this genetic marker – this can be factored in mathematically, but it makes for a less compelling report – I know of no lab that is using, AABB accreditation guidelines, SNPs for family studies.

Ancestry testing companies are under no obligation to perform work to a particular standard – they are not accredited or audited – but they could be doing the best work, mediocre work, slap-dash work. I guess the best way to decipher if an Ancestry test is accurate is to perform the same test, with the same people 5 to 10 times with the same company to see if the result is the same.


The main difference between DNA relationship testing like DNA paternity test and Sibling DNA test versus an Ancestry Sibling DNA tests is, there are no guidelines, audits, or accrediting bodies that can provide checks and balances to the type testing being performed. If you are in need of legal sibling DNA testing learn more here.

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