DNA tests for genealogy: which one answers your question
Every test is a database play. The science is broadly similar; what differs is who else has tested, because a match only helps if the other person is in the same pool.
Match the test to the question
| Question | Test type | Why |
|---|---|---|
| Who are my close cousins, and can I build a tree from matches? | Autosomal (family finder) | Matches across all lines, back roughly five to seven generations; depends entirely on database size |
| Which surname line do I share with this match? | Y-DNA | Follows the direct paternal line only, but survives many generations |
| Where did my mother's maternal line come from? | Mitochondrial (mtDNA) | Direct maternal line only; slow-mutating, so deep ancestry rather than recent cousins |
| What is my ethnic breakdown? | Autosomal | Useful context, unreliable at fine resolution; treat percentages as estimates that change between updates |
| Are there health indications? | Autosomal with health reporting | Separate product decision with privacy consequences — think before buying |
The database is the product
Autosomal matching only works if your relatives have tested at the same company. The largest pools are at Ancestry and 23andMe; MyHeritage is strong in European testers, which matters if your family emigrated recently; FamilyTreeDNA is the specialist for Y-DNA and mtDNA, and it accepts transfers from other companies for a fee, which is often the cheapest way to test one kit in several pools.
You can also upload an existing autosomal file to some services at low or no cost, which is worth doing before buying a second kit.
What DNA does not do
It does not prove a relationship on its own. A shared segment suggests a connection and an approximate cousin level; it does not tell you which of four possible lines it came through. The work is building a mirror tree for each significant match and finding the common ancestor by elimination — that is where most people give up, and where professional help is genuinely useful.
Privacy deserves a thought before you spit: your results reveal information about relatives who did not consent, and matching databases are searchable by law enforcement under varying policies at different companies. Read the specific policy of the company you choose rather than the general marketing.
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