Are Online DNA Tests Accurate?

Online DNA tests are tempting. With a little cash and a little spit, you can learn all sorts of things about yourself – or can you?

A whole lot of people are sending off their spit in the mail. According to a study conducted at MIT, more than 26 million people have taken a genetic ancestry test. And the number of tests purchased in 2018 surpassed sales for all previous years combined.

To see if these online DNA tests are accurate, Live Science journalist Rafi Letzter sent off several DNA samples under fake names to three different companies: AncestryDNA, 23andMe, and National Geographic.

Each test correctly identified his Ashkenazi Jewish heritage, but they failed to agree on the percentage.

AncestryDNA results:

• 93% European Jewish
  • 2% Iberian Peninsula

AncestryDNA results (sample 2):

• 92% European Jewish
  • 3% Iberian Peninsula

23andMe results:

• 91% European Jewish

National Geographic results:

• 88% Jewish
  • 10% Italian/Southern European

National Geographic results (sample 2):

• 85% Jewish
  • 13% Italian/Southern European

The companies’ failure to produce consistent results from the same biological sample is a bit surprising. However, the differences between companies are common. They can be attributed to three things: the method by which a company turns samples into information, the interpretation of that information, and the company’s genetic database.

Your results from a DNA test can even change over time as a company signs up more participants and gathers more data. In the case of Letzter, an update from 23andMe told him he was 100% Jewish. Studies confirm that even identical twins will receive different results from a DNA test.

“Discrepancies in ancestry testing don’t mean that genetic science is a fraud, and that the companies are just making up these numbers,” writes Vox contributor Brian Resnick. “They have more to do with the limitations of the science and some key assumptions companies make when analyzing DNA for ancestry.”

Keep in mind the human genome has roughly 3 billion bits of information. These tests do not look at every piece. Instead, they examine specific positions in your DNA that are of interest (for example, a genetic predisposition to heart disease or balding).

To make things even more complicated, just because you have a gene variant associated with a trait doesn’t necessarily mean you will have that trait. Genetics is all about probability, and there are no genes guaranteed to produce particular traits.

 All told, there is little a DNA test can tell you that will outweigh standard lifestyle advice (i.e. get enough sleep, don’t smoke, etc.).

A DNA test can help identify close family members like siblings and parents. But for distant connections, a test cannot really tell you where your ancestors came from. It simply tells you where you can find DNA like yours on Earth today. To say you are 10% Scottish or 20% Icelandic holds little scientific meaning.

“Ancestry itself is a funny thing, in that humans have never been these distinct groups of people,” explains Alexander Platt, an expert in population genetics at Temple University in Philadelphia. “So, you can’t really say that somebody is 92.6% descended from this group of people when that’s not really a thing.”

Researchers are forced to make decisions when dividing groups of people, but these boundaries are mostly imaginary, continues Platt.

“Certain peoples are more closely related to each other than to other peoples, and [commercial DNA companies] are trying to create boundaries within those clusters. But those boundaries never really existed, and they aren’t real things.”