Discover the truth behind six common genetic genealogy misconceptions—and figure out how DNA testing really fits into your
family tree search.
Jenny Oligos suspected that her great-grandparents had
emigrated from Piraeus, Greece, just like her friend Helen’s (Helen and
Jenny have the same maiden name), but she couldn’t locate the
documentation to prove her hunch. After years of scouring immigration
records, she finally found her holy grail.
second cousin who collected family heirlooms gave Jenny their
great-grandmother’s hairbrush, which still contained a few wispy
strands. Jenny had heard that scientists can use the DNA in hair to
trace a person’s genetic origins. She carefully wrapped the brush and
sent it to a DNA testing company for analysis. Because Helen had
already confirmed through records that her ancestors had emigrated from
Piraeus, she sent a sample of her own hair to the company for
Six weeks later,
Jenny received a full report that provided the answers she’d sought for
years. Not only did she find out that her ancestors had in fact hailed
from Piraeus, but she also learned that she and Helen are fourth
The company even
identified who Jenny and Helen’s common ancestors are. Cousins
currently living in Greece had obtained samples of their ancestors’ DNA
by exhuming their bodies. They’d submitted the DNA samples to the same
testing company, which maintains a database genealogists can use to
find genetic matches. Now that Jenny has identified her family’s
origins, she can focus her research efforts.
this tale of genealogical discovery sound far-fetched? That’s because
it is. Jenny Oligos is a figment of imagination. The story illustrates
common misconceptions about DNA testing, the latest trend in family
history research and the source of much confusion—and even fear. Let’s
tackle those misconceptions one by one so you can learn the
truth about your genetic genealogy testing options.
Myth 1: Geneticists use hair and blood samples to trace a person’s ancestry.
scientists do utilize hair and blood samples for paternity tests and
forensic analysis, there’s no need to draw blood or pluck hairs for a
genetic genealogy test. When you order a DNA test for yourself or
someone else, you’ll receive a cheek-swab kit or a mouthwash kit in the
mail—complete with instructions, a consent form and a return envelope.
For the cheek-swab kit, you’ll use a sterile swab or toothbrush-like
device to painlessly scrape the inside of your cheek for a few seconds.
(The company may provide multiple swabs in order to obtain backup
cheek-cell samples, just in case the first one doesn’t yield clear
results.) For the mouthwash kit, you’ll swish the supplied rinse for a
specified amount of time and spit it back into the container. Then
you’ll just sign the consent form and mail it and your DNA sample back
to the company. You should receive results in the mail or on a
password-protected Web site within a few weeks.
check: So could “Jenny” have sent her
great-grandmother’s hair to a DNA lab for testing? There are forensic
labs that test hair, but this type of analysis comes with a much higher
2: A DNA test can pinpoint precisely where your ancestors lived or
which tribe they belonged to.
your ancestors and their offspring had stayed in one geographic region
and never allowed outsiders to enter, it would be relatively easy to
distinguish their DNA (and yours) from the DNA of people living in
other regions. Over time, all of the inhabitants of your region would
come to share specific genetic mutations (usually harmless changes in
DNA), which would identify them as a distinct population, the same way
a surname identifies members of a family.
our ancestors didn’t stay in one place. For thousands of years, humans
have moved about, leaving their genetic imprints wherever they
procreate and making it increasingly difficult for geneticists to
distinguish one region’s population from another’s.
can make inferences about your ancestry based on trends among
populations, but they can’t say for sure that your ancestors lived in a
specific country, much less a specific town. Testing companies analyze
a person’s genetic makeup by comparing his or her DNA to a reference
database of DNA samples from modern individuals living in various
regions—such as residents of present-day African countries (turn the
page for more on African-American DNA testing). But it’s important to
keep in mind that today’s inhabitants of a given region are genetically
different from the people who lived there before migration occurred.
Just because your DNA matches the DNA of someone who currently lives
there, that doesn’t necessarily mean your ancestors came from that
place. Likewise, your DNA might match that of a modern-day African
tribe, but your ancestors may not have identified with that particular
such as DNA Testing
DNA Fingerprint tests will estimate
where in the world your ancestors originated. Yet scientists haven’t
agreed upon definitions for even broad genetic ethnicities, so if you
test with more than one company, you may get different
By combining genetic
genealogy and traditional genealogical research methods, however, you
can make headway in pinpointing your family’s origins. As more people
get tested and contribute both their DNA test results and their family
trees to online databases (see myth 5 for more on these), scientists
will be able to identify additional patterns and draw better
check: While browsing a database, Jenny might have
noticed that her close relatives’ DNA matches the DNA of people with
confirmed roots in a certain part of Greece. She could then focus her
research efforts on that locale. But at this point, it’s unrealistic to
expect a DNA testing company to provide that level of assurance in your
3: To find out if you and another researcher descend from the same
third-great-grandfather, you need to dig up his body for a DNA sample
strongly recommend letting Great-grandpa rest in peace. There are
easier ways to prove a genetic link that don’t involve literally
turning relatives over in their graves.
find out if you and someone else descend from the same male ancestor,
you should turn to Y-DNA testing. The Y chromosome (also called Y-DNA)
is passed virtually unchanged from father to son, just like (in most
cases) a surname. So Great-grandpa should have the same Y-DNA as his
son, his son’s son and so on. You can use Y-DNA to trace your paternal
lineage, which is represented by the top line of a pedigree chart.
If you and your fellow
researcher are both male and have the same surname as the man you think
is your third-great-grandfather, then you both should have your Y-DNA
tested. (Even if one of you has a different surname, you still could be
related; a surname might’ve changed after an adoption or during an
immigrant ancestor’s assimilation process.) If you’re indeed related,
your Y-DNA test results should be identical or nearly identical,
because mutations do occur occasionally.
even with a perfect match, there’s no telling whether you’re related
through your third-great-grandfather or a different ancestor, unless
you can find the records to prove your hypothesis. That’s because
mutations don’t occur at regular intervals, so it’s hard to predict
exactly when the most recent common ancestor (MRCA) might’ve lived.
Most DNA testing companies provide an estimate, though.
women don’t have Y chromosomes, a female researcher would need to turn
to someone with the same Y-DNA as her biological father. She could ask
her father, brother, uncle (her father’s brother), a male cousin (her
father’s brother’s son) or a nephew (her brother’s son) to take a Y-DNA
Geneticists use another type of
DNA, called mitochondrial DNA (mtDNA), to trace maternal lineage,
what’s shown on the bottom line of a pedigree chart. Mothers pass their
mtDNA to their daughters and their sons, but only daughters pass mtDNA
on to the next generation. Genealogists can use mtDNA in much the same
way as Y-DNA, although it’s not as useful because it doesn’t correspond
to surnames. Plus, mtDNA mutates more slowly than Y-DNA does, making it
even harder to predict when an MRCA might’ve lived.
genealogists use mtDNA to explore their ancient ancestry or to weed out
people who aren’t related through their maternal lines. If your mtDNA
results don’t match exactly with someone else’s, you’re probably not
closely related. Rarely do two people with one or more differences in
their mtDNA have a common ancestor who lived recently enough that she
might appear in written records.
your own or a close relative’s Y-DNA or mtDNA can reveal information
about your paternal line (your father’s father’s father) and your
maternal line (your mother’s mother’s mother) but not about anyone in
between. But you can enlist the assistance of your male and female
cousins to learn about the ancestors named in the middle of your
To find out if they’re related, Jenny and Helen
could’ve had their mtDNA tested (using cheek-cell or saliva samples,
not hair). If their results had revealed an exact match, though, Jenny
and Helen couldn’t have known when the MRCA on their maternal line
lived without turning to traditional roots resources—that ancestor
could’ve walked the earth hundreds of years ago.
two women also could’ve asked male relatives to get their Y-DNA tested.
The DNA company would have been able to use those test results to
estimate with more precision when the MRCA on their paternal line
might’ve lived—for instance, a 12-marker match might mean there’s an 80
percent chance they share an ancestor within the past 15
generations—but again, this would be just an estimate. Geneticists
wouldn’t be able to tell them that they’re fourth cousins. Which leads
us to the next myth.
4: The results of ancestral DNA tests are 99.9 percent accurate, just
like the DNA tests on CSI.
genealogy isn’t an exact science—it involves quite a bit of
interpretation. Although your DNA doesn’t lie, scientists use it to
calculate the probability that you and another researcher are related
or that you have African roots, based on genetic patterns they’ve
observed in populations. This means that genetic genealogy can suggest,
but not prove, a relationship.
test results in particular must be taken with a grain of salt, because
scientists haven’t agreed upon definitions of genetic ethnicity. What
makes interpreting results from biogeographical tests even trickier is
that these tests rely on autosomal DNA, a mixed bag of genetic
information inherited from both mothers and fathers. A test may suggest
that you have some American Indian ancestry, but you won’t know whether
it comes from your mother’s side or your father’s side unless both of
your parents get tested as well. Nor will you know how long ago your
American Indian ancestor (or ancestors) lived.
Y-DNA test results also presents some challenges. The number of Y
chromosome markers you get tested influences the reliability of these
tests. Men can choose to test between 12 and 67 markers. The more
markers tested, the greater the chance of finding genetic mutations (or
differences) and, therefore, the smaller the chance of having an exact
genetic match. In other words, a 67-marker test is more precise than a
12-marker test, and less likely to imply a “false positive”
relationship. It’s also more expensive.
two men have the same surname and the same Y-DNA test results, there’s
a very good chance they’re related within a genealogically significant
time period. One or two different marker values, depending on the
number of markers tested, also could indicate a genetic link. Remember
that a genetic mutation can occur at any time, so even a father’s and
son’s results might not match exactly, although this rarely
The Sorenson Molecular Genealogy
(SMGF), which offers Y-DNA,
mitochondrial DNA and autosomal
databases, generally recommends that genealogists order 36-marker Y-DNA
tests. According to the SMGF Web site, two men with the same surname
who match 34 out of 36, 35 out of 36, or 36 out of 36 markers probably
have a common ancestor who lived within the past 500 years. Two men
with different surnames but with at least a 34 out of 36 match also may
have a common ancestor who lived in the recent past. Fewer matches may
indicate a connection before the widespread use of public
Geneticists know that some
markers mutate faster than others, and they take this into
consideration when interpreting test results. But you can see why
different mutation rates can make predicting when an MRCA might’ve
lived even more difficult.
check: Again, a testing company wouldn’t have told Jenny
and Helen how many generations back their MRCA lived. The company might
have provided a range based on probability.
5: If you take a DNA test, you can finally find out who your
great-grandmother’s parents were.
DNA test results won’t reveal your ancestors’ names, but you can use
them to do a little detective work online. Plug your Y-DNA marker
values—or your relative’s—into a public DNA database, and you may
connect with other genealogists who have the same haplotype.
(“Haplotype” refers to a series of marker values. Your haplotype is
essentially a list of numbers, each corresponding to a DNA
You may find that
people with the same haplotype as you all live in the same region or
even the same country. Although you won’t know for sure that your
ancestors hailed from that place, you may want to do some further
investigating in written records. Of course, you’ll want to pay
particular attention to any genetic matches whose surnames are the same
or similar to yours. By swapping notes with these DNA cousins, you
might just figure out who your great-grandmother’s parents were. But
you won’t make this discovery through DNA testing alone.
of which company provided your test, you can contribute your results to
any public online database. Once you sign up for a database, you may
receive an e-mail notification each time someone with your haplotype
adds his test results. We also recommend joining a surname or
geographic project to meet people who share your surname or whose
ancestors lived in the same region as yours. You can join a project
before or after having your DNA tested.
can upload your DNA test results and your family tree to Web sites such
SMGF database. Once you meet genetic matches, you can let them view
your family tree online, which saves you the trouble of mailing files
back and forth.
check: A DNA test can’t tell you your ancestors’ names,
let alone the ancestors you share with someone else. But if you connect
with a researcher whose haplotype matches yours, you may add to your
family tree simply by sharing what you already know.
Myth 6: “Big Brother” could get your DNA if you try genetic genealogy.
the idea of your DNA test results’ ending up in an online database make
you nervous? Testing companies take your privacy seriously, and they
won’t post your results on the Internet without your consent. If you do
want to include your information in an online database, you can
determine how much personal information you want to reveal.
companies also make a point of safeguarding customers’ DNA
specimens—attaching a bar code, not personal information, to each
sample, for instance. Some companies destroy all samples after
analyzing them. Others give customers the choice of having their
specimens destroyed or allowing the company to securely store their
samples for any additional tests. To learn more about a company’s
though Y-DNA is passed from father to son, a Y-DNA test isn’t a
paternity test. The results can disprove paternity, but they can’t be
used to prove paternity in court. Law enforcement officials could
potentially use DNA test results databases to further an
investigation—a controversial topic in the scientific community—but
it’s unlikely they’d be able to identify a specific suspect using
genetic genealogy research.
check: Rest assured. Getting your Y-DNA or mtDNA tested
won’t open you up to identity theft, criminal investigation or
paternity suits. But it may introduce you to new research avenues, so
you can write your own (true) success story.
From the December 2009 Family Tree Magazine.