In the world of genetic genealogy, mitochondrial DNA (mtDNA) plays a crucial role in tracing maternal lineages. mtDNA is passed down exclusively from mothers to both sons and daughters and offers valuable insights into our ancestral heritage.
In this blog, we’ll explore the history and importance of mtDNA testing, from its early days to its current significance in genetic genealogy research.
You may remember from biology class that the mitochondria are “the powerhouse of the cell” because they generate energy for the cell. DNA is also found within the mitochondria, and because of its unique inheritance pattern, mitochondrial DNA, or mtDNA, can be used for genetic genealogy to provide information about your direct maternal line (your mom, her mom, her mom, and so on).
Mitochondrial DNA is DNA found outside the nucleus of the cell in the mitochondria. With only 16,569 base pairs, or SNPs (single nucleotide polymorphisms), the amount of DNA found in the mitochondria is small compared to nuclear DNA (chromosomes 1-22, the X chromosome, and the Y chromosome).
mtDNA, just like other DNA, is made up of pairs of the nucleotide bases guanine (G), adenine (A), thymine (T), and cytosine (C). At each position, there is a base pair of G, A, T, or C. Each position is assigned a number.
Because of the atomic structure of these four chemicals, normally, the nucleotide bases will be paired with each other in a specific way, with A and T paired together and C and G paired together.
FamilyTreeDNA was one of the first direct-to-consumer DNA testing companies to offer testing for genetic genealogy, starting in 2000. In May 2000, FamilyTreeDNA launched our first mtDNA test which only covered hypervariable region 1 (HVR1). FamilyTreeDNA quickly added the mtPlus test, covering both HVR1 and HVR2 by 2002.
Other companies offering early testing were Oxford Ancestors, which offered the HVR1 test, GeneTree, which offered HVR1, HVR2, and HVR3 before being sold to Sorenson’s SMGF and eventually Ancestry. Ancestry destroyed their mtDNA database in 2014 and Oxford Ancestors theirs in 2018.
In 2005, National Geographic launched the Genographic Project in partnership with FamilyTreeDNA. The first phase of the Genographic Project covered HVR1, which could be transferred to FamilyTreeDNA for matching. Later phases of the Genographic Project’s test covered only enough mtDNA to provide a haplogroup, and while still available to transfer to FamilyTreeDNA, did not cover enough to provide matching. The Genographic Project stopped offering their tests in 2019 and deleted their database in 2021.
In 2006, FamilyTreeDNA began offering the mtFull Sequence test, covering the entire mitochondria–HVR1, HVR2, HVR3, and the Coding Region. Because the mtFull Sequence covers the entire mitochondria, this test can provide the most matches, the most relevant matches, and your most refined haplogroup.
By the end of 2019, FamilyTreeDNA had discontinued our lower-level mtDNA tests, the mtDNA and the mtPlus, and currently only offers the mtFull Sequence for purchase. Customers with the lower-level tests can upgrade to the mtFull Sequence as well.
Because multiple companies offered mtDNA testing early on, sites where mtDNA data could be transferred for matching were also created. FamilyTreeDNA offered one of these, MitoSearch, from May 2004 until May 2018. The third-party, nonprofit MitoYDNA.org was launched in 2017 and remains an active place for testers to transfer today.
However, there are several types of mtDNA mutations, or changes, that can happen: transitions, transversions, reversions, insertions, deletions, and heteroplasmies.
Transitions are where a purine has mutated to the complementary purine (A G) or where a pyrimidine has mutated to the complementary pyrimidine (C T). Transitions are shown by giving the original value capitalized before the location and the mutated value capitalized after the location. For example, a transition of a C nucleotide at position 146 to a T is shown as C146T.
