The team at Yale was able to download and analyze the raw data set that each company used to perform its calculations.
An entire DNA sample is made up of about three billion parts, but companies that provide ancestry tests look at about 700,000 of those to spot genetic differences.
According to the raw data from 23andMe, 99.6 per cent of those parts were the same, which is why Gerstein and his team were so confused by the results. They concluded the raw data used by the other four companies was also statistically identical.
Still, none of the five companies provided the same ancestry breakdown for the twins.
"We think the numbers should be spot on the same," Gerstein said.
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