DNA Fact or Science Fiction? 6 Genetic Genealogy Myths

DNA Fact or Science Fiction? 6 Genetic Genealogy Myths

Discover the truth behind 6 common genetic genealogy myths and figure out how DNA testing really fits into your family tree search.

DNA Genetic Genealogy Myths Facts

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.

A 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 DNA company for comparison.

Are DNA results really that easy?

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 cousins.

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.

Does 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.

Although 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.

Reality 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 price tag.

DNA Genetic Genealogy Myths Facts

Myth 2: A DNA test can pinpoint precisely where your ancestors lived or which tribe they belonged to.

If 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.
But 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.

Scientists 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 group.

Biogeographical tests such as DNA Testing Systems’ 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 results.

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 conclusions.

Reality 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 test results.

Myth 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 to test.

We 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.

To 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.

But 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.

Because 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 test.

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.

Typically, 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.

Testing 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 pedigree chart.

Reality check

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.

The 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.

Myth 4: The results of ancestral DNA tests are 99.9 percent accurate, just like the DNA tests on CSI.

Genetic 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.

Biogeographical 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.

Interpreting 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.

If 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 occurs.

The Sorenson Molecular Genealogy Foundation (SMGF), which offered Y-DNA, mitochondrial DNA and autosomal DNA databases, generally recommended that genealogists order 36-marker Y-DNA tests. According to the SMGF website, 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 records.

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.

Reality 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.

Myth 5: If you take a DNA test, you can finally find out who your great-grandmother’s parents were.

Your 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 marker.)

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.

Regardless 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.

Reality 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.

Does 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.

Testing 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 privacy policy, check its Web site or make a phone call.

Even 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.

Reality 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.

For more information

DNA Genetic Genealogy Myths Facts

Discover the answers to your family history mysteries using the most-cutting edge tool available. Pick up a copy of Family Tree Book’s bestseller, The Family Tree Guide to DNA Testing and Genetic Genealogy by Blaine T. Bettinger. This plain-English guide is a one-stop resource for how to use DNA testing for genealogy.


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  1. “Myth 6” is actually 100% true. Today, June 2, 2018, on CNN.COM, regarding the capture of the Golden State Killer, is reads, “Earlier this year, police tracked him down by comparing genetic profiles from genealogy websites to crime scene DNA, according to investigators.”

    There is a 100% chance that by submitting your DNA it will be handed to the FBI for inclusion in the database they search when they have unknown DNA at a crime scene. It’s a complete invasion of privacy. Seems Ms. Gamber needs to be a more thorough journalist before making statements like, “Rest assured. Getting your Y-DNA or mtDNA tested won’t open you up to identity theft, criminal investigation or paternity suits.”

    The exact opposite is true. You can “rest assured” that getting your DNA tested WILL OPEN YOU UP TO CRIMINAL INVESTIGATIONS. This article should be amended with this major warning.

    • Hi Ken,

      This article is actually being fully re-written and will be available at this URL in the next 6-8 weeks. Thank you for your notes and feedback, we hope you enjoy our updated article.