The mtDNA Test Explained
An mtDNA test can identify other people that are descended from the same female somewhere up the line. mtDNA can be unchanged over hundreds of years, so it can’t tell you whothe common ancestor is – it could be somebody very distant or a much more recent relative.
Everybody has mitochondrial DNA (mtDNA) inherited from their mother, which they inherited from their mother over generations. Sons and daughters both inherit mtDNA, but it’s only the daughters that then pass it on to their children.
It’s possible that a person may share mtDNA with a descendent of direct-line females, but while males may also share mtDNA with another person, they are unable to pass it down to others.
Test other mtDNA lines
Though mtDNA is most commonly associated with tracing back maternal lines, you can also trace back using your father and his brothers and sisters to identify the mtDNA of their mother’s maternal line. This allows you to investigate other maternal lines genetically if you can find a relative who descends from a different line in your own ‘tree’.
The relative you test doesn’t have to be female, but their mother should be directly descended through the relevant maternal line. It’s common for you to be able to test a father, paternal uncle, or child of a paternal uncle to help you discover the mtDNA of your paternal grandmother’s own maternal line.
If you are using mtDNA tests for genealogical purposes, these can only be conducted through Family Tree DNA, and it’s important if you do decide to go down this route that you do their Full Mitochondrial Sequence (FMS) test. If you did one of their earlier mtDNA tests that only checked a portion of your mtDNA, you can log into your account and order an upgrade to FMS.
Some testing companies report mtDNA haplogroup predictions when providing autosomal DNA test results, but they are not comparable in terms of detail and reliability with an FMS test.
The main reason for this is that they don’t test every SNP in the mitochondria, only the ones that are branch-defining, which means the produced data is not as strong.
Furthermore, they do not compare your mtDNA with others to generate a list of maternal line matches.