DNA Fact or Science Fiction? 6 Myths Explained

DNA Fact or Science Fiction? 6 Myths Explained

There is a lot of misinformation and half-truths floating around about taking a DNA test. Before you spit or swab, 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

Nearly every day there is a new story of someone who has successfully found information about his or her family using a DNA test. Adoptees are finding their birth families, donor-conceived children are calling up their biological fathers, and regular genealogists are breaking down brick walls and determining their ancestral origins. There are an equal amount of stories that caution against taking the test, claiming your privacy is at risk and the tests themselves are inaccurate. However, with three kinds of DNA tests (mtDNA, Y-DNA, and autosomal DNA) and the ubiquitous amount of information freely flowing from a myriad of sources, not every news reporter is getting their facts straight. In fact, many are contributing to myths about what DNA testing can and can’t do.

Let’s examine 6 popular ideas about what a DNA test can or can’t do. We’ll make sure we set the record straight and set realistic expectations about what to expect from genetic genealogy.

1. I only need one kind of DNA test

Autosomal DNA

There are actually three kinds of DNA tests that can be useful in family history. We most often hear about autosomal DNA, as it is the kind that reveals our biogeographical origins (ethnicities) and connects us to living cousins. You get half of your autosomal DNA from your mother and half from your father. Thus, it can help you with genealogy questions on both sides of your family. However, because of the way it is inherited, autosomal DNA can only help you back about 6 generations.


The Y chromosome (also called Y-DNA) is passed virtually unchanged from father to son. It can help you answer family history questions back at least 10 generations! So a great-grandfather 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. Y-DNA testing can help you sort out individuals with the same or similar surname into family groups, or help you find a surname for a foundling or adoptee.

Because women don’t have Y chromosomes, a female researcher who wants to trace her direct paternal line will need to turn to someone with the same Y-DNA as her biological father. She could ask her father, brother, paternal uncle, a male cousin (her father’s brother’s son) or a nephew (her brother’s son) to take a Y-DNA test.


Mitochondrial DNA (mtDNA), is used to trace a direct maternal line. Mothers pass their mtDNA to all of their children, but only daughters pass mtDNA on to the next generation. Genealogists can use mtDNA in much the same way as Y-DNA. mtDNA mutates more slowly than Y-DNA does, making it even harder to predict when you should look for your connecting ancestor. However, it can go back just as far in your family tree.

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 find a common ancestor who lived recently enough that she might appear in written records.

The takeaway: Depending on your research goals, you may need all three kinds of tests!

2. You can get DNA from stamps or hair samples to use in your research

Just last year, the answer to this question would have been “unfortunately, no.” While there is DNA on licked stamps and envelopes, used razors, and in the root of your hair (not cut hair), it is a bit tricky to extract. We call this category of samples “special samples” as they lay outside the traditional process used by our Big 5 genetic genealogy companies (23andMe, AncestryDNA, Family Tree DNA, LivingDNA, and MyHeritage).

Sample submission methods

When you order a DNA test, you’ll receive a cheek-swab kit or a spit kit in the mail. It comes complete with full instructions. For the cheek-swab kit, offered by Family Tree DNA, LivingDNA, and MyHeritage, you’ll use a sterile swab to painlessly scrape the inside of your cheek for a few seconds. (The company will 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, used by 23andMe, you’ll swish the supplied rinse for a specified amount of time and spit it back into the container. At AncestryDNA, you are required to fill a small tube with your saliva. No matter the collection method, you return your sample to the company. They include return packaging in the kit, making it easy to drop in the mail. In a few weeks, you will be notified by email when your results are complete. You will be able to view them on your password-protected website.

Direct comparison

While expensive, you can use special samples to perform a direct comparison of the DNA of a postage stamp to a living person to determine parent-child relationships. It can be done at companies outside of the Big 5 genetic genealogy companies. This was also performed by LivingDNA in a case involving DNA collected from a postage stamp. This special case helped a woman, who was found as a baby in a blackberry bush, locate her family. However, so far, none of the Big 5 have extracted DNA from a special sample and compared it to their entire database to find genetic cousins.

It’s possible to do

We know this can be done, as that is exactly what the investigators in the Golden State Killer case did. They took a special sample from a crime scene, extracted the DNA and obtained a DNA profile similar to those generated by the Big 5. They then compared it to the genetic genealogy database found at www.gedmatch.com. Since this case broke in April of 2018, several other cold cases have been solved using this method.

LivingDNA has already indicated it is willing to take on your special samples, and likely it will only be a matter of time before more of the Big 5 will offer this kind of special sample service. There is a new Australian company called To The Letter DNA that is offering DNA extraction from your stamps and letters. However, there is no guarantee that any company will be able to produce a useable DNA profile, and even trying is very expensive.

Not a current option

It is easier to get mitochondrial DNA (mtDNA) from a special sample, if you are interested in direct maternal line research. However, the only company offering a comparison database for mtDNA is Family Tree DNA, and they are not currently accepting special samples.

So, can you get DNA from stamps or hair to use in your research? The answer is a tentative yes.

Is taking a DNA test the right move for you?

3. A DNA test can pinpoint locations where your ancestors lived or tribes they belonged to

A DNA test can pinpoint locations where your ancestors lived or tribes they belonged to. Locating your ancestors’ tribe or location truly is the holy grail of genetic genealogy. Unfortunately, much like the grail itself, it is quite illusive. Even just the word ethnicity is enough to get some people’s dander up. There are conflicting opinions about what that word even means. Some of the categories defined by DNA companies are purely geographical, like Ireland or Germany. Others are cultural, like Jewish or Inuit.

The importance of movement

As Shannon Combs-Bennett points out in her webinar, “What’s Up With My Ethnicity Estimates?, the ethnicity reports are based on a modern interpretation of ethnicity and culture. 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.

Understanding trends

Scientists can make inferences about your ancestry based on trends among populations, but they currently 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. This is a very key idea: that we are using modern day populations to help us make predictions about where our ancestors lived anciently. The Big 5 testing companies are doing their best to use current knowledge about populations and migrations and very advanced statistical data to give us these estimates, but in the end, it is just an estimate; their best guess as to where you might find your ancestors.

Of the Big 5, LivingDNA is coming the closest to pinpointing specific geographic regions. Currently, they’re for those with connections to the British Isles. They break down the UK into 42 different categories. They are currently the only company to be able to provide that level of distinction.

AncestryDNA also offers an interesting view of your origins in their Migrations tool. That tool aims to show you where your ancestors were, not thousands of years ago, but between the years 1750 and 1900. By defining this timeline, they are often able to better deliver origins results that match up with what you already know about your family history.

The best strategy

The best way to use your DNA test results to identify your family origins is to combine them with traditional genealogical research methods. As more people get tested and contribute both their DNA test results and their family trees to online databases, scientists will be able to identify additional patterns and draw better conclusions.

However, if it is deep ancestral origins you seek, you could turn to the mtDNA or Y-DNA test to trace a direct maternal line or direct paternal line origin. The origin information for these two tests comes in the form of a haplogroup, and is initially often very broad and vague, providing you with insights like, you are African, or you are European. But sometimes just knowing that much can be helpful. You can get this kind of haplogroup information from Family Tree DNA, 23andMe, and LivingDNA.

In summary, your DNA test might give you a bit of insight into where your family may have lived, but at this point, it is unlikely to significantly impact your genealogy.

4. The results of ancestral DNA tests are 99.9% accurate

In the previous section, we discussed how your origins, or biogeographical results are just an estimate, so they aren’t meant to be accurate in the sense that they tell the whole story of your family history. 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. Plus, because you only got half of your DNA from your mom and half from your dad, at best, you could only tell 50% of your mom’s story and 50% of your dad’s story.

However, in addition to the biogeographical results provided by our testing company, we receive a list of DNA cousins. All but one of the Big 5 companies provides this list, with the 5th, LivingDNA, planning to release this feature in the fall of 2018.

Understanding cousin matching

In general, cousin matching in genetic genealogy isn’t an exact science—it can involve quite a bit of interpretation. However, if you are asking your DNA to tell you about immediate family relationships, it is very good at that. It is extremely accurate at determining parents, siblings, half-siblings, and aunts and uncles. But after that, we are always going to be dealing with probabilities, which means we will have to use other sources of information to help us make the best decision. In the end, you cannot prove a cousin relationship based on DNA testing alone. You will need to have the paper records to back you up.

Cousin matching with Y-DNA and mtDNA

When we turn to the direct line Y-DNA and mtDNA testing, this idea of accuracy totally changes. Because Y-DNA and mtDNA cannot identify you uniquely, they cannot specifically define any kind of relationship. Very simply stated, if you match on the Y-DNA, you could be brothers or 6th cousins. Matching on the mtDNA is even worse, you could be sisters, or 20th cousins.

The amount of mtDNA and YDNA testing can certainly influence your results. For example, men can choose to test between 12 and 111 markers, or locations, on the Y-DNA. The more markers tested, the better able we are to determine a relationship range. For that reason, a 67-marker test is more precise than a 12-marker test at determining if and when you share a common ancestor, and therefore is less likely to imply a false positive relationship. A false positive is when you match someone on the Y-DNA that you aren’t actually related to. Some men share their 12-marker Y-DNA profile with thousands of people, but only a handful share their 67-marker Y-DNA profile.

Relationships and Y-DNA

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 father and son might not match exactly.

Relationships and mtDNA

Conversely, mtDNA changes relatively slowly, so usually, you will find you have exact matches with many individuals with whom you do not actually share recent common ancestry. In that sense, mtDNA is not very “accurate” at telling you if you do or don’t share common ancestry with someone else.

Are DNA test results accurate? Autosomal DNA test results are very good at determining immediate relationships. Other relationships and other tests will need more interpretation before any solid conclusions can be drawn.

5. If you take a DNA test, you can find out who your great-great-grandparents were

An autosomal DNA test can help you identify genetic cousins, but it can’t tell you exactly how you are related. Your DNA testing company will provide an estimate of your relationship, indicating that you are 3rd cousins, or perhaps even more vaguely, 3rd to 5th cousins. It is left up to you to figure out how. This is no small feat. For example, you and a third cousin should share a common set of great-great-grandparents. You have 8 sets of those! So you have to figure out which one of the 8 sets is the one connecting you.

How do you accomplish this? You do genealogy. If another descendant of your great-great-grandparents has been tested, they might be able to help you connect to them.

Other options

You could also use Y-DNA to help you in your search. However, one limitation of Y-DNA is that even with a perfect match, in most cases, you can’t prove whether you’re related through your great-great-grandfather or a more distant ancestor. You’ll need to try to find the records to prove your hypothesis.

Likewise, you could employ mtDNA to help, but you would have to be very targeted. For example, if you know that Janice is a documented direct maternal descendant of a great-great-grandparent couple, and you believe you too are their direct maternal descendant, then you could compare Janice’s mtDNA to your own. If you match, there is a good chance that you are on the right track.

The answer then, is yes, DNA testing can be a great tool to help you find your 2X great-grandparents. However, it will also take a significant amount of good ol’ fashioned genealogy research.

6. The government or insurance companies can use your genetic genealogy data against you

Does the idea that your DNA test results end up in an online database make you nervous? Testing companies take your privacy seriously, and they won’t integrate your results into the online matching database without your consent. If you do want to make your information available to genetic cousins, you can determine how much personal information you want to reveal. You don’t even have to use your real name. That said, sometimes, companies offer new features or update their terms. Check back periodically to make sure nothing is appearing that shouldn’t.

Specimens are protected

Testing companies also make a point of safeguarding customers’ DNA specimens by attaching a bar code, not personal information, to each sample. You can choose to have their specimens destroyed or allow the company to securely store your sample for any additional tests. To learn more about a company’s privacy policy, check its website.

Public databases vs. testing companies

Remember that in cases like the Golden State Killer, law enforcement used the public database of Gedmatch to make their query. It was not DNA they got from any of the testing companies. However, this is relatively uncharted territory, so it is wise to fully investigate each testing company thoroughly before agreeing to provide them with your genetic samples. Encourage others to do the same.

To ensure that you are maximizing the benefits and reducing the risks of genetic genealogy, just read every form. Be sure you fully understand what a company can and cannot do with your DNA.

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.


  2. Hello, Interesting article. However, I have a question regarding the accuracy of these tests. Some 11 years ago, my partner and I took a DNA test, which revealed at the time, pretty much what we suspected about our ancestry (we were both born in the same town In Yauco, PR). At the time we were happy to have “evidence” that confirmed our Native American ancestry. We both scored 19% and 22% Native respectively. A few years later the tests were updated. We figured why not let’s do it again! This time our Native ancestry went down 4 points on her and 6 points on mine 15% to 16% !!
    At least we were both close in ancestry,, but that was a big drop, or so we thought! We took another test just last year she is now 11% and I am 14%! I can understand that with test refinement and the advancement of science that more is known today than 11 years ago. My question is are we to assume that the other tests were NOT true reflections of our genetic make-up? In 5 years will we still have Native ancestry? It seems to me that these tests are more about money than they are about science.

    At one point I read that in the older tests people searching for Native ancestry were given high native American percentages sort of to “lure” clientel hoping to connect to Native ancestry. This is in fact, one of the reasons why these companies died out. However the same can be said about these new tests. After all, I suddenly feel like spending money, yet again to reconfirm what was confirmed 11 years ago.