About that DNA Test You Got for the Holidays… Part 1

Everyone’s doing it, which sounds like a comment made at a high school party. But according to recent reports, more than 14 million DNA testing kits have been sold – by one company alone! It’s anyone’s guess how many total kits have been actually processed (vs. sold), but the number could easily reach 20 million in 2019.[1] This post will tackle the most popular type of test, autosomal DNA (atDNA). Future posts will address privacy and the two other types of DNA tests taken for genealogical research: mitochondrial, also known as mtDNA, and Y-DNA.

23 chromo

There are loads of articles and Internet searches for “Best DNA Test kit,” but I have yet to find an article in a major media outlet that was written by a genealogist. If you ask a genealogist which testing company is best, I would hope they would turn around and ask you a question or two back, because like all things genealogy, DNA testing is personal, and there is a lot to consider.

If you were to ask me, my first question would be: Why do you want to take the test?

Possible answers:

  • I want to know my ethnicity
  • I want to get my family tree

Let’s pause here. These are the two most common responses I hear, and the ones I spend the most time discussing. DNA testing doesn’t really do either of these things well, even though the commercials promise otherwise.

Here’s the deal. Autosomal DNA tests (atDNA), the most common tests on the market, run from $50-80 or so, depending on the company and the sales. Companies promise your ethnicity estimate(s), and some say that can get to a very granular level with the tests. How do they do that? Beware: science content ahead – or more accurately – beware: statistics ahead!

An atDNA test uses data from the sequence of information on a person’s 22 autosomal chromosomes.[2] The testing company compares individual’s atDNA results to reference samples, looking for identical or similar strands of DNA on the different chromosomes, known as markers.

The data for the reference samples comes from individuals tested with known ancestry from a specific region, going back many generations. These samples help to establish unique genetic signatures from divergent regions around the globe. DNA testing companies take these reference samples and create proprietary databases, which form the basis of the ethnicity estimates.

Scientists still face challenges in this emerging field of study. The analysis is limited by the reference populations used. To date, only a few ancient human remains have yielded usable atDNA,[3] so the reference populations rely on living samples. Results can change as more data and refinement of reference populations change. Each company has a proprietary database, so one person testing with different companies will quite possibly receive different results.

The results are limited by the reference samples (populations) used in the analysis, therefore it is important to remember that the test provides only an ethnicity estimate, and sometimes the tests do not reflect the historic paper trail.

The discussion might continue with some follow up questions: But the results say I’m [Spanish, French, Scandinavian, etc.] but none of my ancestors are [Spanish, French, Scandinavian, etc.]. Is my grandfather not really my grandfather? Where is my German? Is the research you did for me wrong?

No, the historic research isn’t wrong, and though non-paternity events do happen, remember these are ethnicity estimates. The ethnicity of people from Europe is particularly challenging to pinpoint,[4] as brilliantly explained in the maps at this blog entry at DNAeXplained.[5] Think of it this way: could you really tell the difference between someone from Illinois vs Missouri vs Wisconsin? Or Connecticut vs. Massachusetts vs Vermont? How can we expect DNA to know the difference between France and Germany when the borders of those countries changed many times in the last 300 years?

Remember, ethnicity estimates are predictions limited by the reference samples (populations) used in the analysis, and because of the limitations of the reference samples, sometimes the estimates do not reflect the historic paper trail.

Given the political climate of the past few years, I have to raise another, more ominous reason I’m not so keen on the ethnicity estimates: nationalism.

For a lot of places in Europe, the country some DNA kits assign to the results might not have been a country when your ancestors lived there. Germany, not a country until 1871. Italy? Same. Poland, and many other places in Eastern Europe, didn’t exist or had ping pong borders until after WWII, and for some, not until the break-up of the Soviet Union. Current country borders in Africa and South America do not resemble their pre-colonial kingdoms and tribal regions.

Why do we want to plant a flag on our DNA? Sure, it’s cool to know where you are from simply by spitting or swabbing, but the negative undercurrent of relying on ethnicity estimates to “prove” whiteness or align with a certain country or nationality or race needs a careful eye.[6]

Now, about that family tree. Many people assume that when they receive the results of their DNA test, the website will display an amazing family tree. This might happen if you test and match with a relative who has done extensive work, but most of the time, there will be no tree.

Why do genealogists want their clients to test? It’s for the matches. The matches are the prize. Matches allow genealogists to break down brick walls, determine unknown maiden names, locate lost family, rebuild broken branches of trees, and more. Matches are essential tools, particularly if an adoptee is seeking information on a biological family.

How do matches work? Aren’t they just estimates, too? In a word, no. Matches are hard science, comparing your DNA with others who have also tested with the same company. If you match with another person who tested at the same company, it means that both of you have an ancestor in common.

Two main factors influence the significance of a match between people: the number of segments of matching DNA; and the length of the matching segments. The longer and more prevalent the strands, the closer the match. Using these matches, genealogists can start to piece together unknown branches of a tree. This work can be challenging, take patience, and time.

Another essential question to ask yourself regarding DNA testing: have you prepared yourself for the possibility of unexpected results? Have you considered how you will approach family members, or strangers, when communicating about results, expected or not?

Don’t be afraid to jump into DNA testing for genealogy. Just be sure to do it with your eyes, and not just your mouth, wide open.


Finally, the information in this post is based on my experience testing myself, family members and clients, as well as my study of DNA testing for genealogy. I do not receive advertising or other revenue from any of the DNA testing companies. I am not a lawyer and please do not consider this legal advice.

[1] “Autosomal Testing Growth,” The DNA Geek, https://thednageek.com/dna-tests/, accessed 30 Dec 2018

[2] “Autosomal DNA,” International Society of Genetic Genealogy, https://isogg.org/wiki/Autosomal_DNA, accessed 23 Dec 2018

[3] “Ancient DNA,” FamilyTreeDNA research group, https://www.familytreedna.com/groups/ancient-dna/about/background, accessed 2 January 2019

[4] There are some exceptions, notably the autosomal DNA of people with Ashkenazi ancestry.

[5] “Ethnicity is Just an Estimate – Yes, Really!,” DNAeXplained – Genetic Genealogy, https://dna-explained.com/2018/12/28/ethnicity-is-just-an-estimate-yes-really/, accessed 30 Dec 2018

[6] “Written in Blood,” Joan Donavan, Anthropology News. http://www.anthropology-news.org/index.php/2018/07/12/written-in-blood/, accessed 20 Dec 2018

Image: Bolzer et al., (2005) Three-Dimensional Maps of All Chromosomes in Human Male Fibroblast Nuclei and Prometaphase Rosettes. PLoS Biol 3(5): e157 DOI: 10.1371/journal.pbio.0030157 Image 7a, https://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0030157, used under Creative Commons Attribution 2.5 Generic license, accessed 3 Jan 2019


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