How do DNA ancestry tests work?

After you send a saliva sample, the lab extracts DNA and uses a chip to read around 600,000 to 700,000 single-letter variations called SNPs, out of the roughly 3 billion letters in your genome. Your markers are compared with reference panels of people whose families have lived in one region for generations, producing an ethnicity estimate that is a statistical best guess rather than an exact answer. Relative matching is more precise: the company finds other customers who share long stretches of identical DNA, measured in centimorgans, and predicts how closely you are related. Ancestry has built a database of over 25 million people. In 2025, 23andMe filed for bankruptcy and was later bought by a non-profit led by its co-founder, highlighting privacy questions about genetic data.