What is mtDNA?
Mitochondrial DNA (mtDNA) is found in the mitochondria of human cells. Each cell can contain several mitochondria, and each mitochondrion contains dozens of copies of mtDNA. So in every cell there can be thousands of copies of mtDNA. This is different from nuclear DNA, since we only inherit two copies of the autosomal and sex chromosomes per cell.
All of us inherit our mtDNA from only our mothers. This mtDNA essentially remains unchanged through the maternal line, providing an incredibly useful way to trace maternal ancestry.
What is mtDNA sequencing?
The circular mitochondrial genome has three regions – two small hypervariable (HVR) regions and a large coding region. It is possible to sequence just the HVR1 region, both hypervariable regions (HVR1 and HVR2), or the complete mitochondrial genome (HVR1, HVR2 and the coding region).
The hypervariable regions comprise approximately 1100 bases of the mtDNA genome. Most of the variation in the mtDNA occurs in these regions. If two people have a perfect match at their HVR1 and HVR2 regions, further analysis of the much larger coding region can provide a higher stringency comparison and further resolution. The coding region covers the remainder of the mitochondrial genome and the complete mitochondrial genome is 16,569 base pairs.
The entire DNA sequences for regions tested are provided to you in your mtDNA test report. Your mtDNA sequencing results are compared to a reference sequence called the “rCRS” (revised Cambridge Reference Sequence), and all of the positions within your mtDNA, which differ from rCRS are listed in your report.
Your unique mtDNA sequence result is known as your mtDNA profile.
Since mtDNA is passed down from mother to child along the direct maternal lineage, people who have descended from the same maternal lineage are expected to have exactly the same or very similar mtDNA profiles.
If two people have different mtDNA profiles, it conclusively confirms that they did not descend from the same maternal lineage.