Are DNA tests for ancestry accurate?

dna testing for ancestry accuracy

DNA tests for ancestry and genealogical purposes are just twenty years old. In 2020, FamilyTree DNA was the first-ever company offering customers the possibility to collect a DNA sample at home to understand family history better. To date, millions of tests have been conducted, and the databases of the main players offer the possibility to connect with a distant cousin from anywhere in the world.

The results are getting more precise, and people have great fun tracking back their family lineage. This trend is expected to continue to grow. GlobeNewswire estimates that in 2027, the market size for ancestry DNA tests will reach a staggering $10 billion.

Most tests just cost around $100. For this price, it is possible to get a peek into the family’s past and reconstruct our ancestors’ migration, at least partially. The main question, though, relates to the accuracy of these genetic analyses. Are they reliable enough to be used confidently? What are the factors influencing the results?

Assuming that you know that the DNA is composed of 3 billion chemical elements, it is easy to understand that at-home ancestry tests come with an approximative accuracy.

In this article, we will dig deeper into the key elements that influence the test results.

Number of regions, markers, and size of the database

Most of the tests work on the same scientific principles. Generation after generation, the DNA will slightly mutate. The process is very slow, but these differences will allow tracking back the migration of your ancestors and defining what your genetic make-up is.

Hence, a Japanese will carry genetic markers known as Single Nucleotide Polymorphisms (SNP) that will differ from a native American.

The DNA is extracted from a saliva sample, and the code of life will be analyzed using micro-array chips that will recognize the SNPs within the DNA. Hence, the more SNPs analyzed and the higher the accuracy of the test. Check this article to know more about the scientific basis of such analyses.

Some of the most well-known at-home DNA testing companies rely on 700,000 genetic markers dividing the world into thousands of regions.

Below are the regions used by the most popular tests available.

Analyzing many markers and regions is good, but your DNA sample will ultimately have to be compared to a reference database. AncestryDNA is very transparent about the size of its own reference population composed of nearly 45,000 samples.

Always make sure that the regions are regularly updated. Nebula Genomics uses Whole Sequencing Technology, and their partnership with FamilyTreeDNA increases the chances of finding relevant information.

For DNA Genetic genealogy, data is critical. The more comprehensive the database, the better and more accurate the results.

Uncontaminated DNA sample

Most of the companies rely on a spit sample. Saliva contains cells from numerous body origins and allows to extract a sufficient amount of DNA. Take care somehow that the cells are really your own.

A couple of years ago, a group of journalists conducted a little experiment. They sent DNA samples from Bailey, a sweet Golden Retriever dog, to numerous supposedly reputable companies. Most of them returned the results as unreadable, but at least one uploaded a comprehensive report about Bailey’s Health. This would be funny if people did not rely more and more on at-home DNA tests for genealogy and health-related advice.

More seriously, the technology is now robust enough to provide accurate results, but it is advisable not to perform the test following a bone marrow transplant or stem cell therapy. This is because the donor DNA may be picked up and will increase the genetic background noise, leading to unreliable results.

Company accreditations

Most of the companies offering DNA for health-related purposes need to be cleared by the FDA. This is not the case with Ancestry DNA testing. As we mentioned earlier, most companies currently on the market use the same type of technologies and rely on DNA chips and SNPs. They are looking at a small portion, 0.02 percent, of the 3 billion human DNA pairs bases.

Full Genome Sequencing is different, but the results will always be as good as the size of the underlying database.

The International Society of Genetic Genealogy (ISOGG) is very active and provides information on the quality of the tests offered by the companies. Check their website to know more details about the quality of the various tests currently available.

Users are usually frustrated by the fact that the results are provided as potential ethnicity percentages. It is important to understand that Genetic Genealogy is a probabilistic science. Do not expect to receive a family tree going back up to the Romans. What you will always be a probability. In that sense, Genetic genealogy is very close to weather forecasts.

To wrap up

Genetic genealogy can be quite fascinating, but even if most companies rely on sound scientific principles, the lack of accuracy of the results can be frustrating. Do not expect a simple saliva sample to unveil your family history up to the dawn of time.

Nonetheless, with companies continuously expanding their databases and number of DNA markers, the results will only get better with time. So favor companies that update the results as more scientific evidence becomes available. Most of the big market players do just that.

As for accuracy, be careful to collect DNA as instructed and not to contaminate the sample. DNA tests for ancestry analysis are still and will continue to be a work in progress. However, it doesn’t mean that these tests have no value.

For example, it is always quite fascinating to get in touch with a distant family member living in Dublin while the rest of the family has moved to the US at the dawn of the century.

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