When it comes to genetic genealogy (which I often refer to as genetealogy), Y-DNA is by far the most popular type of testing–and understandably so. Since Y-DNA is passed from father to son down through the generations (just like surnames) its application is fairly obvious. But over time, mitochondrial DNA (usually shortened to mtDNA) testing has been gaining in popularity.
How mtDNA Travels
Many folks regard mtDNA as the equivalent of a maternal version of Y-DNA testing and while there are some parallels, there are also some differences, and that creates a lot of confusion.
For instance, mtDNA is passed down through maternal lines, but mothers pass it on to both their sons and their daughters. The sons, however, become mtDNA dead ends and do not pass it on. This means that a brother and sister (who share the same mother) can both get tested for mtDNA, and that they both can serve as living representatives of their mother, their motherâ€™s mother, their motherâ€™s motherâ€™s mother, and so on. (Think of the bottom line of a pedigree chart). But when this brother and sister pass on, her children will continue to sport the same mtDNA, while his will have his wifeâ€™s mtDNA.
Primarily a Deep Ancestry Tool
Perhaps the most important aspect of mtDNA to grasp is that itâ€™s essentially a deep ancestry test, and is not as genealogically useful as Y-DNA. If youâ€™re familiar with Bryan Sykesâ€™s best-seller, â€œThe Seven Daughters of Eve,â€ you may recall that the underlying premise is that 95 percent of people of European origin can trace their maternal roots to one of seven women who lived in Europe approximately 10,000-45,000 years ago.
I, for example, am from haplogroup H (haplogroups might be thought of as branches of the worldâ€™s family tree–in this case, the worldâ€™s maternal family tree), which Sykes dubbed Helena. Her descendants were the most successful in reproducing. Consequently, roughly 30-40% of those of European origin are also H. And this, in turns, means that I have millions of maternal cousins. Thatâ€™s not tremendously helpful to know when it comes to tackling my family tree.
Are You My Cousin?
Unfortunately, a lot of genetealogy newbies fail to understand this, so once they get their results, they tend to play the matchmaking game. By this, I mean that they e-mail everyone who matches their mtDNA, share the usual name/place/date details of their direct maternal line back to their earliest-known ancestor, and then cross their fingers hoping for someone to report back having found some overlap. But because itâ€™s such a massive fishing expedition, this hardly ever happens. (I know of one success story, and in my mind, this person hit the mtDNA lotto!)
Given its limited utility, why would folks even be interested in taking mtDNA tests? One reason is simple curiosity. A lot of people are genuinely interested in knowing about their deep ancestry. So if you want to know roughly when and how your direct maternal line migrated out of Africa, you might take this test to find out. For most folks, this is all they will learn, but for many, itâ€™s sufficient.
Three Exceptions andÂ . . .
Having just said that mtDNA tests are not very helpful for genealogical purposes, Iâ€™d like to point out a few important exceptions:
- First, you might be lucky enough to have rare mtDNA (taking the tree analogy a little further, you could think of this as coming from a branch or even a twig with very few leaves on it). This was true of Ann Turner, who co-authored â€œTrace Your Roots with DNA: Using Genetic Tests to Explore Your Family Treeâ€ with me. Some people like Ann have very few, if any, mtDNA matches. Even though she is also in haplogroup H, the most common European one, she has a couple of additional mutations that reduce the number of exact matches all the way down to one. In cases like this, it makes sense to play the matchmaking game and compare notes.
- Second, you might be dealing with degraded remains, as is often the case with history mysteries. For instance, I recently worked on a BBC show to try to identify the two skeletons found in the turret of the USS Monitor a few years ago. In cases like this, scientists would love to use Y-DNA, but itâ€™s too fragile and doesnâ€™t survive. MtDNA, by contrast, is plentiful, so it is more resilient. Itâ€™s not as precise, but itâ€™s usually all scientists have to work with. So in this case, I took the maternal lines of the sailors who lost their lives in the USS Monitor, and traced them forward in time to find living maternal relatives to serve as a basis for comparison to the DNA extracted from the remains. This is also what I routinely do on my cases for the U.S. Armyâ€™s repatriation project (to help identify remains of servicemen still unaccounted for from WWII, Korea, and Southeast Asia).
- Third, you may have a specific, maternally-oriented genealogical conundrum–and if youâ€™re strategic about it, you just might be able to come up with a clever way to resolve it using mtDNA testing. There are a few examples on pages 69-73 of â€œTrace Your Roots with DNA.â€ (Those who are registered at Amazon can use the â€œsearch inside this bookâ€ feature to view these pages or you can click here for a detailed version of one of the examples given).
. . . A Couple of Caveats
To this list of exceptions, I now need to add a pair of qualifiers. The good news is that testing companies and avid genetealogists are working together in an attempt to refine haplogroups. For instance, when I first got my mtDNA tested several years ago, I learned that I was H. Now I can find out that Iâ€™m H1*. Returning to the tree analogy, itâ€™s somewhat akin to learning which twig off of the H branch my maternal line comes from.
Also, mtDNA is finite. It has 16,569 base pairs, which sounds like a lot, but is nothing compared to the billions of bases found in nuclear DNA thatâ€™s used for Y-DNA tests. So itâ€™s in the realm of the possible to test for your entire mtDNA sequence, which translates into very precise results.
The catch? Well, there are two. Once you have your sequence, you can theoretically play the matchmaking game again, but at prices currently in the $795-895 range, you probably wonâ€™t have too many to compare against until prices come down. And I need to point out that a full-sequence mtDNA test is the first genealogical one that could conceivably give away medical secrets. Some conditions are passed through maternal lines (e.g., some kinds of muscle disorders), so your results could potentially reveal more than youâ€™d care to know. Of course, youâ€™d have to take your results (which are well-protected) and do some fairly intensive research or consult a genetic counselor, but in the interest of full disclosure, I feel obligated to mention this possibility.
Hop in the mtDNA Pool!
If youâ€™re new to genetic genealogy, I know this is a lot to absorb, so Iâ€™d suggest that you start with more conventional Y-DNA testing, perhaps joining a surname project. But if youâ€™re ready to take the next step or are just plain curious, I hope this primer will help you understand just what you can and canâ€™t learn from mtDNA testing.
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Megan Smolenyak Smolenyak, co-author (with Ann Turner) of Trace Your Roots with DNA: Using Genetic Tests to Explore Your Family Tree (as well as In Search of Our Ancestors, Honoring Our Ancestors and They Came to America), can be contacted through www.genetealogy.com, www.honoringourancestors.com, and megansrootsworld.blogspot.com.
Upcoming Events Where Megan Will Be Speaking
— Joint Genealogical Speakers Guild and International Society of Family History Writers and Editors luncheon at the FGS conference
(September 2, 2006 – Boston, MA)
— David Ackerman Descendants 1662
(October 21, 2006 – Ramapo, NJ)
— 2006 Genealogy Conference and Cruise (hosted by Wholly Genes Software)
(November 11-18, 2006 â€“ Mexican Riviera)
Details and links to upcoming events