GENEALOGY-DNA-L ArchivesArchiver > GENEALOGY-DNA > 2006-08 > 1155327320
Subject: The ABCs of mtDNA -- Megan's Blog
Date: Fri, 11 Aug 2006 16:15:20 EDT
Just in case anyone is not subscribed to Ancestry.com, and haven't
seen this blog article of Megans, enjoy.
Ancestry Daily News
Megan Smolenyak Smolenyak – 8/4/2006
The ABCs of mtDNA by Megan Smolenyak Smolenyak
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 mother's mother, their
mother's mother'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 wife's mtDNA.
Primarily a Deep Ancestry Tool
Perhaps the most important aspect of mtDNA to grasp is that it's essentially
a deep ancestry test, and is not as genealogically useful as Y-DNA. If
you're familiar with Bryan Sykes's best-seller, The Seven Daughters of Eve, 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 world's family tree--in this case, the world'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.
That'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 it'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, it's sufficient.
Three Exceptions and...
Having just said that mtDNA tests are not very helpful for genealogical
purposes, I'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 Trace Your Roots with DNA: Using Genetic Tests to Explore Your
Family Tree 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
it's too fragile and doesn't survive. MtDNA, by contrast, is plentiful, so it
is more resilient. It's not as precise, but it'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. Army'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 you'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 "Trace Your Roots with DNA." (Those who are registered at
Amazon can use the "search inside this book" feature to view these pages or
you can _click here_
(http://freepages.genealogy.rootsweb.com/~wrhurst/lindsey-kelly/catherinekellyparents.htm) for a detailed version of one of the
...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 I'm
H1*. Returning to the tree analogy, it'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 that's
used for Y-DNA tests. So it'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 won'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 you'd care to know. Of
course, you'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 you're new to genetic genealogy, I know this is a lot to absorb, so I'd
suggest that you start with more conventional Y-DNA testing, perhaps joining a
surname project. But if you'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
can't learn from mtDNA testing.
About the Author
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 her websites _Genetealogy.com_
(http://www.genetealogy.com/) , _Honoring Our Ancestors_ (http://www.honoringourancestors.com/) , and
_Megan's RootsWorld_ (http://megansrootsworld.blogspot.com/) .
Upcoming Appearances by Megan
* 02 September 2006, Boston, Massachusetts
Joint _Genealogical Speakers Guild_ (http://www.genspeakguild.org/) and
_International Society of Family History Writers and Editors_
(http://www.rootsweb.com/~cgc/) luncheon at the _FGS conference_ (http://www.fgs.org/)
* 21 October 2006, Ramapo, N.J.
_David Ackerman Descendants 1662_ (http://ackerman-1662.rootsweb.com/)
* 11-18 November 2006, Mexican Riviera
_2006 Genealogy Conference and Cruise_
(http://www.whollygenes.com/cruise2006.htm) , hosted by Wholly Genes Software
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