First of all, what’s a mitochondria? For those of you who don’t recall your high school biology class: a mitochondria is a structure within the cell. It’s often referred to as a cell’s “energy center.” There’s a really good explanation here. Mitochondria have their own DNA, so they can be tested separately. It was long believed that mitochondrial DNA was only inherited from the mother. That’s no longer true: it’s now known that it’s possible to inherit mitochondrial DNA from both parents. However, that inheritance is still considered to be rare.
What’s a mitochondrial DNA test? Currently marketed by FamilyTreeDNA, these tests are sold as a way to explore the genetic ancestry of a maternal ancestor. Such tests can examine the ancestry of the mother, the mother’s mother, etc. back in a straight maternal line. They can be taken by both males and females, as both should inherit mitochondrial DNA from their mothers.
These tests work by comparing certain markers on the mitochondria with the markers on the mitochondria of other test test takers. Their “genetic distance” is determined by the number of markers they share. This “genetic distance” allows test takers to estimate how many generations back they share a common female ancestor. As with Y-DNA tests, the more markers tested, the more precise the test is likely to be.
These tests are generally not accepted by lineage societies. Mitochondrial DNA mutates slowly, making it difficult to tell how recently two people share a common ancestor – and thus who that ancestor might be. FamilyTreeDNA indicates the following for its most comprehensive mtDNA test: “It means that you have a 50% chance of sharing a common maternal ancestor within the last 5-16 generations (or about 125-400 years).” If you’re thinking of using them to explore your lineage society ancestral line, use them as a way to gather more evidence instead of part of your documentation.