DNA ancestry tests are not ‘crystal balls’—they’re approximations

| | February 5, 2019
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Image credit: CBC
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Identical twins have virtually identical DNA. So you’d think if a set of twins both sent in a DNA sample for genetic ancestry testing, they’d get the exact same results, right?

Not necessarily, according to a recent investigation by the Canadian Broadcasting Corporation. In fact, the journalists demonstrated that twins don’t often get the same results from a single company. And across the industry, estimates of where an individual’s ancestors lived can differ significantly from company to company.

So what accounts for these differences? Overall, discrepancies in ancestry testing don’t mean that genetic science is a fraud, and that the companies are just making up these numbers. They have more to do with the limitations of the science and some key assumptions companies make when analyzing DNA for ancestry.

Related article:  Doctors face 'wrenching questions' about genetic testing and legal risks. Do we need new laws?

What’s not always obvious from these reports is how they’re based on estimates that can vary from company to company, and have built-in sources of error.

“What’s important to understand is that genetics can guide answers” about ancestry, says Joe Pickrell, a geneticist and the CEO of Gencove, a company that sells genetic testing hardware and software to other companies. “There’s no time machine, no crystal ball.”

Even though genetic ancestry tests deliver precise percentages about our heritage, the reports are best thought of estimates, based on imperfect data.

Read full, original post: The limits of ancestry DNA tests, explained

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