Prepared by Elisabeth Lindsay.
Mitochondrial DNA, also known as mtDNA, is the genetic material found in the mitochondria, the so-called "energy factories" of the cell. It is the only type of DNA found outside the cell nucleus. Mitochondrial or mtDNA is passed down through the female line from mothers to both sons and daughters, in contrast to Y-chromosome DNA, which is passed down exclusively from father to son. The mtDNA is also distinct in that sons do not pass down their mother's mtDNA to their children, but daughter's do. The mtDNA test is one type of DNA test used in the field of genealogy.
The mtDNA test does little to solve one's immediate research problems: it is often used to chart one's deep ancestry or ancestral group, unlike the Y-chromosome DNA test that can be used to chart the father to son paternal line from the present to the past, for as far back as the paternal line remains unbroken. A broad sampling of mtDNA collected across cultures is used to determine the ancestry of various human groups and the early migration patterns of humans around the world, as in the National Geographic, Genographic Project.