What does a genealogy DNA test actually measure?

A laboratory reads selected markers in your genome and compares them with other people in the same database. It is not a full genome sequence and not a medical diagnosis. The useful output is a list of matches who share segments with you, plus a model-based ethnicity estimate.

What is the difference between autosomal, Y-DNA and mtDNA?

Autosomal DNA comes from both parents and is the usual family-history test, reliable for a limited number of generations. Y-DNA follows the direct paternal line only. Mitochondrial DNA follows the direct maternal line and changes slowly, so it is weaker for recent cousin identification.

Can an ethnicity estimate prove where an ancestor was born?

No. The estimate compares your segments with the company's current reference panels, which change over time. Use it as a hint about regions to search. A birthplace still has to come from a record that names a town, parish or commune.

What is a centimorgan and does it name the relationship?

A centimorgan is a measure of shared DNA used as a probability, not a relationship label. The same total can fit several relationships. You choose among them with shared matches and with paper: censuses, marriages and the trees those matches attach.

Should I download my raw DNA data?

Yes, as soon as the company makes it available. Databases close and firms merge. A file you control lets you upload to another matching pool later and keeps you from losing the laboratory work if an account disappears.

Can DNA replace birth and marriage records?

No. DNA is excellent at grouping living testers around a recent ancestral couple. It does not name maiden names, village spellings or exact parent pairs. Those still come from civil and church acts that you can open and cite.

Are genealogy DNA test kits free?

The laboratory work is not free. What can be free is uploading a raw file you already paid another lab to generate, or viewing a relative's match list. Advertisements that say free usually mean a bundle, a transfer, or something that is not a genotype at all.

How do I use matches without exposing living relatives?

Link matches to people on a tree you control, work in shared-match clusters, and keep living people out of public views unless they agreed. A test that finds a parent can also publish a family secret. Confirm interesting links with records before you send messages that assume the relationship.

How Genealogy DNA Tests Work | Blog

How autosomal, Y-DNA and mtDNA tests differ, what ethnicity estimates can and cannot prove, and how to use matches with a sourced family tree.