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Travel obligations and internet issues are going to be interfering with daily posts for at least some of the next 10 days to two weeks. So nobody will go into withdrawal, however, The Legal Genealogist offers…

The term of the day:

MITOCHONDRIAL DNA.

Frequently on Sundays, we review the different types of DNA and DNA tests. But there’s one, I think, that often gets us a bit confused.

See, on one hand, we have YDNA — the kind of DNA contained only in the Y chromosome that only men have, and is passed down from father to son to son with relatively few changes through the generations.1 The Y chromosome is one of the two chromosomes that determines whether you’re male or female. With an X and a Y, you’re male. With two X chromosomes, you’re female.

So when we move over to mitochondrial DNA (mtDNA) — the kind of DNA passed down from a mother to all of her children and that only her daughters can pass on to their children2 — people often think that it comes from the woman’s X chromosome.

Nope. It’s found in the mitochondria (singular: mitochondrion) that aren’t even in the same parts of our cells as the chromosomes. Here’s what the National Library of Medicine has to say:

Although most DNA is packaged in chromosomes within the nucleus, mitochondria also have a small amount of their own DNA. This genetic material is known as mitochondrial DNA or mtDNA. Mitochondria are structures within cells that convert the energy from food into a form that cells can use. Each cell contains hundreds to thousands of mitochondria, which are located in the fluid that surrounds the nucleus (the cytoplasm).3

So in this image, you’d find all the chromosomes — the autosomes and the X and the Y — inside the nucleus. The mitochondria are a whole ‘nother part of the cell. We do also get information useful for genetic genealogy from the X chromosome — but that’s not done through mtDNA testing.

cell


SOURCES

  1. ISOGG Wiki (http://www.isogg.org/wiki), “Y chromosome,” rev. 10 Oct 2013.
  2. ISOGG Wiki (http://www.isogg.org/wiki), “Mitochondrial DNA,” rev. 20 Jul 2013.
  3. What is mitochondrial DNA?,” Genetics Home Reference Handbook, National Library of Medicine, US Department of Health (http://ghr.nlm.nih.gov/handbook : accessed 12 Oct 2013).
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