Term of the day: Mitochondrial DNA

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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6 Responses to Term of the day: Mitochondrial DNA

  1. Thanks for this post, Judy. I had my mtDNA tested by Sorenson ages ago – back around 2003, I think – got my results back, and frankly have never understood the value of it as it tells me nothing except I fall within Haplogroup N, Sub Haplogroup X2, with my ancestors found most commonly in the Americas and W Eurasia. I had some men contact me with the surname of my paternal grandmother, who have been trying desperately to connect my tree to theirs, but I don’t know how to help, since there are no brothers here and I can’t seem to find a male 1st cousin of mine to submit to a DNA. I guess the newer tests done today would give me more of a genetic map, do you think?

    This information about the mitochondria you have posted is very interesting. I had no idea! Thanks for all the information you give us!

    Judy

    • Judy G. Russell says:

      The newer tests will help, Judy, but remember that the men who contact you on mtDNA can only link their mothers’ lines to your mother’s line, so that’s where to look for any common mtDNA ancestors.

      • Thanks for the clarity of this explanation, Judy. So, it sounds to me as if there is no way the person I mentioned (male) and I could possibly have a common mtDNA ancestor unless, as often happens, our lines cross by brothers and sisters marrying siblings, somewhere back along the way. Do I understand that correctly?

        • Judy G. Russell says:

          Not exactly. You each get your mitochondrial DNA from your mothers, so it would have to be his maternal line and your maternal line crossing somewhere back in time.

  2. Jana Last says:

    Judy,

    Thanks for this informative post. I just recently ordered the mtDNA Plus test from Family Tree DNA. I received the Family Finder test results not too long ago. So interesting!

    I want to let you know that your blog post is listed in today’s Fab Finds post at http://janasgenealogyandfamilyhistory.blogspot.com/2013/10/follow-friday-fab-finds-for-october-18.html

    Have a great weekend!

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