Until a few years ago, most ancestry tests for individuals relied on short stretches of DNA in cell-powering organelles called mitochondria, which are inherited through the mother, or on the Y chromosome, which a father passes down to his sons. While providing very accurate information about father/son relationships, these tests were not always so accurate about the geographical origins of earlier ancestors.
For example, a set of Y-chromosome markers called Haplogroup R1b is common among Western European men, but a small fraction of North Africans have it, too. Similarly, “if men have a Y chromosome that is more common in Scandinavia than England, they’re convinced they’re a Viking”, says Mark Jobling, a geneticist at the University of Leicester, UK. But that is not necessarily the case. Such nuances are not always conveyed by the companies that offer such services, notes Jobling. What’s more, Y-chromosome or mitochondrial markers trace only one strand in a person’s ancestry.