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This Is How Home DNA Ancestry Kits Work

23andMe personal genetic test saliva collection kit, with tube, box and instructions.

Ancestry DNA tests have been popular for a few years, and it’s easy to see why. Unlocking the secrets of your past by simply swabbing your cheek sounds almost too good to be true. Unfortunately, DNA testing is far more complex and far less informative, than you might think.

There are a whole host of organizations that offer to test your DNA for around $100, but the big three are 23andMe, Ancestry.com, and Heritage DNA. All three sites provide similar products and databases, with additional services like DNA health testing available for an additional fee.

The DNA kits don’t directly tell you anything about your ancestry despite the marketing promises. Here’s how they actually work.

Basic Tests Aren’t Mapping Your Entire Genetic Code

Blue helix human DNA structure
Billion Photos/Shutterstock.com

You can have your entire genome mapped through a process called DNA sequencing, but that’s going to cost you more than a 23andMe, Ancestry.com, or Heritage DNA kit. Dante Labs is currently offering the service for $600, which is around six times the price of 23andMe’s basic service.

Instead of sequencing, the mainstream services use genotyping, which matches blocks of genetic code from individual samples to sequences found across large groups. This method is quicker and cheaper than DNA sequencing.

Sequencing would also be overkill when it comes to DNA ancestry services. They function by grouping people based on their DNA and require an extensive database. The reduction in price means more people can afford to take part, and the database becomes larger as a result. And the blocks of code that the company genotypes are enough to group people by ancestral background.

Mainstream Kits Don’t Tell You About Your Ancestors

When you submit your test, you aren’t just giving the company your DNA; they also know where you are currently living. DNA ancestry testing works by comparing your genetic information and personal details with other people who have submitted DNA kits. It then uses that data to find clusters of genetically linked people around the globe.

How Do These Kits Work?

A 23andMe Ancestry Breakdown
23andMe/Dave McQuilling

Mass migration events have happened throughout history, but populations tend to settle between these periods. So theoretically, an Irish person is likely to be genetically closer to another Irish person than a person from Outer Mongolia. A more significant number of samples will provide greater accuracy.

There are also issues with this kind of testing. Firstly, you need a high takeup globally to ensure accuracy. If entire ethnic groups or countries are left out, samples close to those groups will either be some kind of “unknown” or more likely just matched to the nearest possible source. For example, if a DNA testing service had no clearly identified “Scottish” samples, someone with 100% Scottish ancestry may be labeled as a random English, Irish, and Scandinavian mix.

One of my great-grandfathers immigrated from Romania. Unfortunately, Romania may not have a large uptake as, despite Mr. Constantinesque contributing around 8% of my DNA, no “Romanian” springs up in my DNA results. I do have about 8% worth of either “Greek & Balkan, broadly Southern European, and Iranian according to 23andMe—or “2% Southern Italy, 6% Eastern Europe, and Russia” according to Ancestry.com. All of this makes sense if you look at the historical record and compare the invasions and migrations to your genetic makeup. But filling in the blanks like this says nothing about your personal family history and can’t be considered 100% accurate.

So What Do These Tests Tell You?

Ancestry.com's DNA Map

A DNA ancestry test can’t tell you about your personal family history and what individuals you are related to have done during specific time periods. It actually tries to tell you is where people you are genetically close to are living now. Companies use two methods to do this, and both are flawed. They record the locations tests are sent in from, and survey users about their family history.

The obvious flaw in the survey method is not all answers are going to be accurate. Sure, people have traced their family trees back hundreds of years—but things like infidelity and adoption can make some of that research unreliable. And relying on family stories may not be accurate either. Great-Grandpa was actually Hungarian and not just a shady guy on the run and in need of a back story? Ok.

The other method matches your DNA to participants in other countries. Because the population of the USA is a mix of people from around the globe, tests submitted by non-native Americans can’t really be used for much. DNA testing might let you know you have a lot of DNA in common with people from Montana, but it won’t be able to tell you if anyone you are descended from ever set foot in that state.

Because of this, tests tend to give a breakdown of modern European, African, and Asian countries you have genetic ties to. There are issues here too. A lot of European countries, including Germany and Italy, haven’t actually existed for that long—and the majority of African countries were drawn up by European powers in the 1800s. There’s every chance the nationality that allegedly makes up a good chunk of your DNA didn’t exist when your ancestors crossed the Atlantic.

Then there is the fact most of the world was a chaotic, famine and plague-filled, warzone for the majority of human history. The very same things that made your ancestors cross the world and settle in the US also made people shuffle around the old world quite a bit too. There’s no guarantee the DNA of a modern-day Italian or Russian is close to the DNA of someone living on that same piece of land 1000 years ago.

You also need to consider the margin of error. Anything under 2% should be taken with a pinch of salt, and the larger chunks have a margin of error that is often higher than 10%.

So what do the kits actually tell you? They’ll let you know how much genetic material you have in common with Native Americans and other people currently living in Europe, Africa, and Asia. Provided those people have also taken a DNA test with the same company.

You can’t even get a clear idea of which parts of your DNA breakdown come from which parent. It is possible to get a better idea of what parts of your DNA breakdown come from where if you convince both your parents to take a test—but this can be easier said than done. There is also a slight danger you’ll find out a relative isn’t actually a blood relative. These tests can’t tell you much about your family’s ancient past, but they are capable of deciphering enough about its recent past to destroy everyone involved’s lives.

What About Mitochondrial DNA?

A mitochondrial DNA diagram

The closest thing the tests come to matching you with your actual ancestors comes via “Haplogroup reports.” These tests use mitochondrial DNA to trace a user’s maternal line, and male samples can also have their paternal line traced through their “Y-DNA”. Like genotyping, this can be used to match samples with large groups and linked to migratory movements tens of thousands of years ago, as well as smaller groups like tribes and clans.

However, this too has limits. The only data comes from your direct paternal lines, and if you’re female, this is limited to your mother’s direct female line. Males taking the tests will also get data from their father’s line. What this means is, you’re only getting data from one or two of your four grandparents, one or two of your eight great-grandparents, and so on. You can learn a little about your heritage this way, but by the time you go back far enough for Y-DNA and Mitochondrial DNA to be useful, you’ll only be getting a small slice of the history pie.

You Can Have Your DNA Compared to Archeological Samples

A breakdown of Ancestral DNA Samples
My True Ancestry

If matching your genetic code to living people isn’t enough for you, some companies will compare your DNA to samples from archeological finds. My True Ancestry is the most popular of these and will attempt to find genetic links between you and people who lived hundreds or even thousands of years ago.

Like the more mainstream services, My True Ancestry provides a breakdown of populations you are related to—But instead of Germans or Iranians; the pie chart shows you groups like Celts or Dacians. The site also shows you how close you are to specific genetic samples. If your ancestor was a gladiator and they have his DNA on file, then you may be in luck!

However, a few glaring issues mean your My True Ancestry results need to be taken with a generous pinch of salt. The most obvious one is: when you trace it back far enough, we are all descended from the same group of people. And this doesn’t mean tracing things back to the dawn of humanity; scientists claim that every European from the 9th century who left descendants is a direct ancestor of every European around today.

“Genetic distance” is also an issue. You can use the percentage of DNA two people have in common to predict their relation to one another—and with close relatives. But when you move past first-cousins, there is a lot more overlap between the exact relationship and the number of genes you will share with another person. Over centuries and tens of generations, it is impossible to state a clear relationship. For this reason, the “genetic distance” score My True Ancestry gives you with specific samples is vague.

Another issue is the sample size. Archeological records make up a tiny percentage of the people who lived during the times those records are from. Like mainstream tests, the more extensive the sample size, the more accurate the results. My True Ancestry only uses a handful of samples; those samples come from individuals whose backgrounds are essentially a “best guess” based on how the samples were found.

Ancestry DNA Testing Is Still Worth It

Closeup of a pile of vintage family photos
Karin Hildebrand Lau/Shutterstock.com

Please don’t interpret this article as some attempt to trash DNA testing. It isn’t. There are many benefits to getting your genetic code analyzed.

The tests are incredibly good at finding your long-lost, still-living relatives. If someone you’re related to has also done a test and doesn’t want to remain anonymous, their results and genetic distance from you will show up in the database. You can use this to connect and potentially share information on your family history.

When it comes to tracing your roots, some information is better than no information at all. 23andMe is putting a lot of effort into helping descendants of enslaved people learn more about their past, as records can be patchy and information on their ancestors before they arrived in the Americas is nonexistent. Adoptees may also know very little about their family background; a test can put them in touch with close relatives who may help them reconnect with their biological families.

Standard tests, and even tests based on archeological samples, may not be able to accurately tell you where your ancestors originated. But, they do get the imagination flowing, and might inspire you to feel a connection with and learn about cultures you never considered looking into before.

So despite all of the flaws, an ancestry test is still intriguing enough to drop $100 on.

Dave McQuilling Dave McQuilling
Dave McQuilling has spent over 10 years writing about almost everything, but technology has always been one of his main interests. He has previously worked for newspapers, magazines, radio stations, websites, and television stations in both the US and Europe. Read Full Bio »