Mitochondrial DNA: Part 1 – Overview

This is Part 1 of a series about mitochondrial DNA, abbreviated as mtDNA, and how to use it successfully for genealogy.

What is Mitochondrial DNA and Why Do I Care?

Mitochondrial DNA.jpg

Mitochondrial DNA is different from nuclear, or autosomal, DNA. Nuclear DNA resides within the nucleus of a cell, while mitochondrial DNA resides outside the nucleus.

Mitochondrial DNA nucleus.png

Every cell has thousands of mitochondria while it only has one nucleus.

Mitochondrial DNA is a circular ring with 16,569 base pair locations. The biological purpose of mitochondria is to power the organism, converting chemical energy into a form that the cells can utilize.

Mitochondrial DNA is also different from autosomal DNA in how it is passed to offspring.

Inheritance Path

Mitochondrial DNA is unique because all people, males and females, inherit their mitochondrial DNA from their mothers, but only females pass it on to their children.

Y and mtDNA inheritance

The chart above illustrates which individuals in your tree inherit their mitochondrial DNA from whom.

Mitochondrial DNA inheritance.png

The daughter and son both inherit their mitochondrial DNA from their mother, who inherits hers from her mother, and so forth – on up the direct matrilineal line. You can read about the difference between matrilineal and maternal lines, here. In essence, maternal can be referring to anyone on your mother’s side of your tree, while matrilineal is your mother’s mother’s mother’s line ad infinitum.

However, every person in this tree carries mitochondrial DNA of specific ancestors.

Mitochondrial DNA inheritance 2.png

The red arrows show the inheritance path of mitochondrial DNA for individuals whose contributors are also in the tree.

The father of the children inherited his mitochondrial DNA from his magenta mother’s matrilineal line.

His father inherited his mitochondrial DNA from his lavender mother’s line.

The maternal grandfather in dark blue inherited his mitochondrial DNA from his red mother’s line.

Mitochondrial DNA inheritance 3.png

The gold arrows show that the contributors of these individuals are not shown on this tree, but they all inherited their mitochondrial DNA from their matrilineal lines as well.

When discussing mitochondrial DNA, we generally think in terms of ourselves, but the application of mitochondrial DNA to genealogy is as far reaching as all of our ancestors.

Each line has its own unique story for us to harvest – assuming we can find an appropriate candidate for testing or find someone who has already tested.

Why Mitochondrial DNA Works

Mitochondrial DNA is inherited from our matrilineal line directly, with no genetic contribution from any males. This inheritance path allows us to use mitochondrial DNA for matching to others reaching back generations as well as providing a way to view beyond the line-in-the-sand of surnames.

In other words, because mitochondrial DNA is not mixed with DNA from the fathers, it’s very nearly identical to our matrilineal ancestors’ mitochondrial DNA many generations ago.

In fact, by tracing a series of mutations, we can track our ancestor over time from mitochondrial Eve, born in Africa tens of thousands of years ago to where we are today.

Mutations Happen

If mutations never occurred, the mitochondrial DNA of all people would be identical and therefore not useful for us to use for genealogy or to peer back in time beyond the advent of surnames.

Mutations do occur, just not on any schedule. This means that it’s difficult to predict how long ago we shared a common ancestor with someone else based solely on mitochondrial DNA mutations.

There might be a mutation between us and our mother, or there might be no mutations for hundreds or even, potentially, thousands of years.

Part of the success of matching genealogically with mitochondrial DNA testing has to do with the regions tested.

Testing fewer locations results in matches that are much less relevant.

The Regions

Mitochondrial DNA is divided into 4 regions used for genealogy.

  • HVR1 – Hypervariable Region 1 – locations 16021-16569 (548 total locations)
  • HVR2 – Hypervariable Region 2 – locations 1-437 (437 locations)
  • HVR3 – Hypervariable Region 3 – locations 438-576 (138 locations)
  • Coding Region – the balance of the mitochondria (15,445 locations)

If you think of mitochondrial DNA as a clock face, the hypervariable regions span the time from approximately 11-1. The Coding Region is the balance.

Mitochondrial DNA loop.png

Family Tree DNA bundles the HVR3 region with the HVR2 region in their results. They test the entire D Loop, meaning a total of 1124 locations in their mtPlus product.

Matching at the HVR1 or HVR1 plus HVR2/3 levels alone can reach back thousands of years in time. I strongly encourage testers to test at the higher full sequence level with the mtFull product, allowing much more granular matching.

The HVR1, 2 and 3 regions are exactly as their name suggests – hypervariable – meaning that they mutate faster than the coding region.

The mtFull or full sequence test tests the entire mitochondria – all 16,569 locations.

Genealogists need a full sequence test in order to do two things:

  • Match with other testers reliably
  • Obtain a full haplogroup which acts as a periscope in time, allowing us to look much further back in time than autosomal and on one specific line. There’s no confusion as to which line the results came from with mitochondrial DNA.

If you’ve only taken the mtPlus test, don’t worry, you can sign on here and upgrade at any time to the mtFull.

Medical Information

The coding region carries most of the potentially medically relevant locations. Medical data is not provided in the results of the testing – only genealogically relevant information.

Family Tree DNA does provide for HVR1 and HVR2/3 results to be shown in projects that testers join, if testers so choose. Coding region results are never shared anyplace unless individual testers share them individually with each other.

I’m personally not concerned about this, but mitochondrial DNA testing has been occurring for 20+ years now and it was uncertain at that early date what medical information might be discovered in the coding region, so the decision to not share was made by Family Tree DNA at that time and remains in effect today.

Today, Family Tree DNA is the only vendor to test your full sequence mitochondrial DNA and provide matching. Therefore, all examples in this series utilize results and tools at Family Tree DNA.

So, what can people see of your actual results?

What Matches See

Mitochondrial DNA match view

You can click this image to enlarge.

People whom you match can see that you do match, but they can’t see any differences or mutations. They see the name you’ve entered, your earliest known ancestor and can send e-mail to you. Aside from that, they can’t see your results or mutations unless you’ve joined a project.

Within projects, participant names are never listed publicly. In other words, your matches can’t tell that it’s you unless they recognize your earliest known ancestor on the project list and you are the only person with that ancestor.

Don’t worry though, because only your HVR1 and HVR2 region results are listed in projects, as shown in the next section.

Benefits of Joining Projects

The great news is that even if you’ve just ordered your test and are waiting for results, you can research and join projects now.

Projects at Family Tree DNA provide testers with access to volunteer administrators to help as well as clustering users in projects that are meaningful to their research.

Mitochondrial DNA hap A project.png

The haplogroup A project is shown above with maternal earliest known ancestor (EKA) names as provided by testers.

Another important project feature is the project map function, allowing testers in a specific haplogroup to view the locations of the earliest known ancestors of other members of the same haplogroup – whether they match each other or not. Your ancestors traveled with theirs and descended from a common ancestor. Cool, huh!

Mitochondrial DNA hap A10 map.png

For example, here’s the haplogroup A10 cluster around Montreal. What’s the story associated with that distribution? Whatever it is, it’s probably important genealogically.

Mitochondrial DNA hap A5a1a1 map.png

Here’s haplogroup A5a1a1 in Japan.

Do you have clusters? You can see if you join relevant projects.

Another type of project to join is a geographical or interest group.

The Acadian AmerIndian Project welcomes descendants who have tested the Y, autosomal and/or mitochondrial DNA of the various Acadian families which includes French and English settlers along with First Nations indigenous ancestors.

Mitochondrial DNA Acadian Amerindian project.png

The map shows the distribution of the haplogroup A2f1a ancestors of various Acadian testers.

Mitochondrial DNA Acadian hap A2f1a map.png

Projects such as the Acadian AmerIndian Project facilitate genealogists discovering the haplogroup and information about their direct line ancestor without testing.

For example, if Anne Marie Rimbault, shown above, is my ancestor, by viewing and hopefully joining this project, I can harvest this information about my ancestor. I can’t personally test for her mitochondrial DNA myself, but thankfully, others who do descend matrilineally from Anne Marie have been generous enough to test and share.

Furthermore, I’ve contacted the tester through the project and gained a great cousin with LOTS of information.

Just think how useful mitochondrial DNA would be to genealogists if everyone tested!

Finding Projects to Join

I encourage all testers to join appropriate haplogroup projects. There may be more than one. For mitochondrial haplogroup J, there is only one project, but for those who carry haplogroup H, there is a haplogroup H project and many additional subgroup projects.

I also encourage you to browse the selections and join other interest projects. For example, there are projects such as Cumberland Gap which is regional, the American Indian project for people researching Native ancestry, in addition to your relevant haplogroup project(s).

When deciding which projects to join, don’t neglect your mitochondrial DNA. Your selection may be a huge benefit to someone else as well as to your own research.

How to Join Projects

Sign on to your personal page at Family Tree DNA and click on myProjects at the top, then on “Join A Project.”

mitochondrial dna project join.png

Next, you’ll see a list of projects in which your surname appears. These may or may not be relevant for you.

Mitochondrial project list

You can click to enlarge this image.

You can search by surname.

Mitochondrial project search.png

More importantly, you can browse in any number of sections.

Mitochondrial project browse.png

For mitochondrial DNA, I would suggest specifically mtDNA haplogroups, of course, along with mtDNA Geographical Projects, Dual Geographical Projects, and mtDNA lineage projects.

Surname projects are more challenging for mitochondrial DNA since the surname changes every generation.

When you find a project of interest, click to read the description written by the volunteer administrators to see if it’s a good fit for you, then click through to join.

Next Article in the Series

Of course, you’re probably wondering what all of those numbers in your results and shown in projects mean. The next article in about a week will address exactly that question.

Reference Articles

These articles may be of interest.

Mitochondrial DNA is often confused with X DNA, and they are not at all the same.

Mitochondrial DNA can quickly confirm or put to rest that Native American ancestor family story.

A great example of using mitochondrial DNA to break through a brick wall that would never have fallen otherwise!

If you haven’t yet tested, your can order your mtFull Sequence test today!

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18 thoughts on “Mitochondrial DNA: Part 1 – Overview

  1. Thanks for the reminder to join a mitochondrial haplogroup project. I just did – and discovered you’re the project administrator (haplogroup B) That has to be a good thing. 🙂

  2. I so appreciate this tutorial! 23andMe, when I tested there, did a projection that my maternal haplogroup was I4. My mitochondrial results (mtHVR1 and mtHVR2, and “mtDNA coding region” according to FTDNA, won’t be ready until June 24 through July 8. Should I join a project before that time? I have no idea which one to join. My most remote maternal line ancestor is only as far as American Colonial. I’m so excited, but I don’t want to put the cart before the horse! –old Colonial phrase….lol!

    • Wow, that’s really unusual. Check to see what is available and you can join projects now. You might want to also join a more specific one after your results.

  3. I actually have a question. I’m waiting on my FamilyTree results now. There is reason to believe my maternal grandmother was not the daughter of her “parents”. Should I show them as her parents anyway? Maybe try to add a note saying they may not be her parents? Not sure how to handle that! Thanks.

    • I don’t think it matters either way. If it’s not long, I would probably just wait to see what the results say.

  4. Thanks Roberta for a great explanation. I’m looking forward to the next posts.
    Would you be able to explain what part of the mitochondria is tested by the Living DNA test and how this compares with the FTDNA tests?
    Thank you.

  5. Hi, Roberta, another great article. I always find your articles on DNA interesting. I have a question relating to the inheritance of mitochondrial DNA. What do you think of recent articles that refer to Taosheng Huang who heads the Mitochondrial Diseases Program at the Cincinnati Children’s Hospital Medical Center who discovered that one of his patients had actually inherited mitochondrial DNA from both of his parents? With more and more people testing their mitochondrial DNA is it possible that this could prove to be more prevalent and how will it affect genetic genealogly?

    • I didn’t mention that because it’s exceedingly rare, 17 people total, and the people were quite ill. I don’t want everyone to suddenly doubt their results based on a medical anomaly.

  6. Hi Roberta,
    Thanks for the great explanations. You made the statement that “every cell has thousands of mitochondria”, which is a bit misleading. According to WikiPedia “The number of mitochondria in a cell can vary widely by organism, tissue, and cell type. For instance, red blood cells have no mitochondria, whereas liver cells can have more than 2000”.
    And “a single mitochondrion can contain 2–10 copies of its DNA”.

    From the “Embryo Project Encyclopedia”: “In humans, the mature egg cell, or oocyte, contains the highest number of mitochondria among human cells, ranging from 100,000 to 600,000 mitochondria per cell, but each mitochondrion contains only one copy of mtDNA.”, which was news to me!

    Looking forward to the next installment on mtDNA for genealogy.
    Thanks, Tammie Gregori

    • You need to test at all 4 companies meaning Ancestry, Family Tree DNA, MyHeritage and 23andMe. He may have tested at any of those. Also, contact the agency and join a registry. You can find the links to order at the bottom of this article.

  7. Pingback: Mitochondrial DNA: Part 2 – What Do Those Numbers Mean? | DNAeXplained – Genetic Genealogy

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