Nearly every day there is a new story of someone has successfully found information about his or her family using DNA testing. 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. However, with three kinds of DNA tests (mtDNA, Y-DNA, and autosomal DNA) and an 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 DNA testing 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.
I only need one kind of DNA test
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, and 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 in to family groups, or help you find a surname for a foundling or adoptee.
Because women don’t have Y chromosomes, a female researcher wanting to trace her direct paternal line 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.
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, but 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.
Therefore, depending on your research goals, you may need all three kinds of tests!
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, on 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
Traditionally, when you order a DNA test for yourself or someone else, you’ll receive a cheek-swab kit or a spit kit in the mail—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, or you want more testing later.)
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 via the regular mail using the enclosed return packaging. In a few weeks, you will be notified by email when your results are complete and you will be able to view them on your password-protected website.
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 which 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
However, 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 like you would receive from the Big 5, and 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.
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, while others are cultural, like Jewish or Inuit.
The importance of movement
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 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 currently coming the closest to pinpointing specific geographic regions for those with connections to the British Isles. They break down the UK into 42 different categories, 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 1,000’s 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 from your traditional research.
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 you family may have lived, but at this point, it is unlikely to significantly impact your genealogy.
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.
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 to those cousins. 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 2X great grandparents. You have 8 sets of 2X great grandparents, meaning that you have to figure out which one of the 8 sets is the one connecting you. How do you accomplish this? Well, you do genealogy! If another descendant of your great-great grandparents has been tested, and this DNA match has a paper trail, they might indeed be able to help you connect to them.
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 whether you’re related through your 2X great grandfather or a more distant ancestor, unless you can 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 the 2X great grandparent couple that you believe to be descendent from, 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, but it will also take a significant amount of good ol’ fashioned genealogy research.
The government 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.
Specimens are protected
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, not one of the Big 5 testing companies. However, this is relatively uncharted territory, so it is wise to fully investigate each testing company before agreeing to provide them with your genetic samples, and 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 and be sure you fully understand what a company can and cannot do with your DNA.
For more information
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.