Two sisters take the same DNA test. The results show that one sister is 10% French, the other 0%. Both sisters share the same two parents, and therefore the same set of ancestors. So how can one be 10% more French than the other? Tests like these rely on our DNA to answer questions about our ancestry, but DNA actually can’t tell us everything. Prosanta Chakrabarty explores the accuracy of DNA tests.

[TED Ed]