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Ancestry Daily News
7/8/2003 - Archive
Genetic Genealogy, Part II: DNA Inheritance
An article that appeared on 03 June provided an introduction to DNA testing
for genealogical purposes and discussed some of its potential benefits for your
research (www.ancestry.com/rd/prodredir.asp?sourceid=831&key=A719401
). A logical next step is to take a look at the origin of your DNA in order
to better understand who might have the "right" DNA to help solve
your genealogical mysteries.
Quick Facts:
1. Only males have a Y chromosome.
2. The Y chromosome is passed from father to son down through the generations
and corresponds to the top, purely paternal line of a pedigree chart.
3. Both males and females have mitochondrial DNA (mtDNA).
4. MtDNA is passed by mothers to both their sons and daughters, but only daughters
pass it on to their offspring. Its most obvious genealogical trail is the bottom,
purely maternal line of a pedigree chart.
5. We all inherit DNA from other ancestors in our pedigrees, but at this time,
the Y chromosome and mtDNA genetic genealogy tests (which analyze our direct
paternal and maternal lines) are the most popular and informative.
Y Chromosome Testing
Y chromosome tests are mostly used for surname studies, but the scope of such
studies can vary greatly. The scope, in turn, helps determine appropriate testing
candidates.
For instance, suppose Jim Jablonsky and Bob Jablonsky are both researching their
family trees and suspect they might share a common ancestor. In such a specific
scenario, it's quite obvious that the people who need to take the test are Jim
and Bob themselves. This is an example of a narrow study.
Looking at the opposite extreme, someone might decide to launch a very broad
surname project focused on a particular surname—say, Swanson. Most likely,
this person would start a website dedicated to the project, issue an open invitation
to any males with the name to participate, and seek out Swanson men to join
in the study. In this situation, participation is also fairly obvious since
anyone with the surname of interest can take a test. Women can also take part
by finding a male proxy—perhaps their father, brother, paternal uncle, paternal
male cousin, etc.—to provide a DNA sample representing their Swanson line.
With such broad projects, the intent is generally to learn as much as possible
about the origins of all people with a given surname. Over time, as more people
are tested, patterns will generally start to emerge. For instance, of twenty-five
men tested, perhaps seven might match each other, another five might match each
other, three other pairs might match each other, and the remaining fellows won't
match anyone. Those who match even one other participant can compare notes to
learn more about their ancestry, since they now know that they share a common
ancestor in their paternal line. Doing so often helps steer future research
by revealing certain geographic areas in which to focus efforts. Those who have
no initial matches may well benefit from a match down the road as the project
continues.
Participation becomes a little less obvious for surname projects that fall somewhere
between these narrow and broad extremes. For example, someone may have a theory
that two Austin families—one with a documented presence in 1700s-era Massachusetts
and one of the same time period in Virginia—share a common origin. Perhaps
both lines had the habit of using certain first names, one or two of which were
fairly unusual, so a connection is suspected.
In such a case, the project manager will need to try to locate a living male
Austin for both of these lines (no need to somehow obtain samples from deceased
ancestors since direct male descendants will have the same Y chromosome). For
the line he has been researching, he probably has a good idea of testing candidates
(he may well be one himself), but for the other one, he'll have to do more genealogical
detective work. Ideally, he would look for a descendancy chart of the originator
of the other line and follow the male lines down the chart to the most recent,
still-living generations. (Descendancy charts begin with a common ancestor and
branch out forward in time to their children, who then in turn branch out to
their children, etc.)
Over time, some lines will "dry up" because some men will have had
no offspring, or at least, no sons, so his focus will be on sons who had sons.
In short, he will be looking for any living man who has an unbroken male chain
back to the ancestor of interest, the originator of the line. In many such cases,
he will end up locating quite a few men who meet the criteria, but since they
all share the same Y chromosome, only one need be tested to represent each line
(although he might wish to test a second in each line as "insurance"
to rule out non-paternity events).
MtDNA Testing
Both males and females have mtDNA, which we receive from our biological mothers.
But as mentioned earlier, males do not pass it on to their children. The easiest
way to find testing candidates for an mtDNA project, therefore, is to focus
on the direct maternal line—daughters of daughters down through the generations.
Fortunately, when you reach the most recent, living generations, you can expand
your search by including living males whose mothers were part of this maternal
line. For instance, if a researcher were trying to find someone to provide an
mtDNA sample to represent a man who died fifty years ago, she could look for
both brothers and sisters of the man in question. If all siblings are deceased,
however, she could look for both sons and daughters of the man's sisters. Children
of the man's brothers, by contrast, will not have the mtDNA she seeks.
For various reasons, mtDNA testing is generally not as genealogically revealing
as Y chromosome testing (unless yours happens to be fairly rare), but it works
well for particular situations. For instance, let's assume that your great-great-grandfather
had twelve children by three wives, but it's not clear which children should
be attributed to each wife. Following the "daughterly chain" to the
present (i.e., daughter of a daughter of a daughter . . .) for each daughter
of your great-grandfather would help assign the children to the correct mothers
(assuming no unexpected complications, such as your great-great-grandfather
marrying a sister of his first wife!). For such a project, you would have to
get a living representative of each daughter's line tested and compare the results.
MtDNA testing is also interesting for what it can reveal about your deep ancestry.
By taking a test, you can discover essentially which maternal "clan"
you hail from and consult resources such as "The Seven Daughters of Eve"
to learn more about where your maternal origins fit into the history of mankind.
To read more and find out which DNA test might be appropriate for your genealogical
research, visit Ancestry.com's website at: http://shops.ancestry.com/product.asp?productid=1025994
. For any questions, please contact Rachael McKinnon, rmckinnon@myfamilyinc.com
Megan Smolenyak Smolenyak, author of Honoring Our Ancestors, In Search
of Our Ancestors, and They Came to America: Finding Your Immigrant Ancestors
can be contacted through www.honoringourancestors.com
. Additional articles on DNA testing for genealogical purposes can be found
at www.honoringourancestors.com/library.html#three.
Upcoming Events
In upcoming weeks, Megan will be at:
--- Williamsburg Visitor Center
(12 July 2003, Williamsburg, VA)
--- ZCMI Center Deseret Book
(17 July 2003, Salt Lake City, UT)
--- FEEFHS International Convention
(18-19 July 2003, Salt Lake City, UT)
--- Family History Fair
(12 October 2003, New York City)
--- New York Genealogical & Biographical Society
(14 October 2003, New York City)
--- NGS Gentech04
(22-24 January 2004, St. Louis, MO)
Details and links to upcoming events.
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