DNA tests for family history
Autosomal, Y-DNA and mitochondrial tests explained, what ethnicity estimates really mean, how DNA matches help break brick walls, which company to test with for UK ancestry, and privacy considerations.
A DNA test won't build your family tree; the records do that. What it does is confirm the paper trail, connect you to living cousins who share ancestors, and occasionally overturn a line that the documents said was solid. Used alongside a properly researched tree it is a powerful tool. Used instead of one it is a list of strangers and a pie chart.
The three kinds of test
| Autosomal | The standard test everyone sells. Looks at DNA inherited from all ancestors over roughly the last five to seven generations and matches you with other testers who share segments. Gives an "ethnicity estimate" as a by-product. Works for anyone, male or female. |
|---|---|
| Y-DNA | Men only; follows the direct paternal line (father's father's father…), which in Britain usually follows the surname. Useful for surname studies and for proving or disproving that two male lines share a common ancestor; useless for any other branch. |
| Mitochondrial (mtDNA) | Follows the direct maternal line (mother's mother's mother…). Changes so slowly that a match may share an ancestor thousands of years ago; of limited genealogical use except to rule a connection out. |
For family history, start with an autosomal test. Y-DNA is a specialist second step.
What the ethnicity estimate means
Less than the marketing suggests. It compares your DNA with reference populations the company has chosen and gives percentages that change every time the reference panels are updated. For British testers the regions are broad ("England and North-Western Europe") and a surprise percentage usually reflects the limits of the method, not a hidden ancestor. Treat it as entertainment; the matches are the science.
How matches help
- A match who descends from the same great-great-grandparents confirms that line on paper is right.
- A cluster of matches all descending from one couple you don't have in your tree points to where a brick wall should be broken.
- Shared matches ("in common with") let you sort your matches into the four grandparent lines.
- Matches with trees save you work; matches without them are leads to write to.
- For adoptees and unknown parentage, matches can identify birth families, with care and often with help from experienced searchers.
Expect many fourth-to-sixth cousins and few close ones. Real progress comes from building the matches' trees back to find the shared couple, which is paper research again.
Which company for UK ancestry
The value of a test is the size of the database you are matched against. AncestryDNA has by far the most testers, including the most British ones, so it finds the most cousins; it only sells autosomal tests and doesn't accept uploads. 23andMe has a large database and health reports. MyHeritage is strong in Europe and accepts uploads from other companies. FamilyTreeDNA is the only one of the four selling Y-DNA and mtDNA tests and accepts autosomal uploads. Living DNA specialises in British regional ancestry. Most serious researchers test at Ancestry, then upload the raw file to MyHeritage, FamilyTreeDNA and the free GEDmatch to fish in other ponds.
Practicalities
- Kits cost around £60 to £100, less in sales; a Y-DNA test from FamilyTreeDNA is more.
- Test the oldest generation first: a parent or grandparent carries DNA you have lost.
- Results take four to eight weeks.
- Link the results to your tree on the site so matches can see how you connect.
Privacy and surprises
You are sharing genetic data with a company and, indirectly, with every relative who tests. Read the consent options (research use, law enforcement matching, visibility to matches) and choose. Be ready for a result that doesn't match the paper: an unexpected parent or grandparent turns up in a small but real proportion of tests, and it affects other living people. Decide before you test how you would handle that.
The test is best taken once the tree is in good order; the beginners' guide gets you there, and the site comparison covers the companies' record collections.