For Christmas a year ago, I received an Ancestry DNA test kit from my daughter. I was excited to receive this gift because the ads for the product were on TV all the time and my curiosity was really piqued. So was my daughter’s. Ancestry DNA’s marketing program had been successful because I couldn’t wait to submit my sample. Our daughter gave herself a test kit, too, not to verify the accuracy of her paternity, but to learn the origins of own heritage.
Well, I’m sorry to disappoint, but I don’t have anything scandalous to report—fortunately. My wife and I sent in our saliva samples and six weeks later we received our results. I didn’t learn anything I wasn’t already suspecting, but it confirmed my origin was 71% England, Wales, and Northwestern Europe, 13% Ireland and Scotland, and 8% each from Norway and Germany. So now that I knew this, what’s next? What do I do with this information? It doesn’t change anything. My son and daughter still have the same father. I already knew my maternal ancestry was German, but some Brits had apparently slipped in there at some time. I also knew the $99 my daughter spent for my test fattened Ancestry DNA’s bottom line.
I really didn’t give it another thought until recently when the Journal of the American Medical Association, JAMA, had a review article about “Genetic Ancestry Testing.” My interest was rekindled, and this blog is the result.
I don’t pretend to know a lot about DNA and genetics, but I took a genetics course in college and biochemistry and molecular biology (called Cell Biology) in medical school. But that was 54 years ago and knowledge of DNA, mitochondria, and gene transmission was in a very early stage. The complexity and utility of this subject has increased considerably as is shown by law enforcement’s reliance on DNA testing for solving crimes and attorneys for paternity determination. These legal determinations require a lot more sophisticated testing than the basic ancestral screening I underwent.
From my reading I got the strong impression that testing by different companies will give you different results. “Ancestry DNA” may determine a different origin for you than “23 and Me.” Oh, really? Yes, that’s what I learned. These companies amass a huge database of genetic information from millions of samples. The majority of genetic studies have been done on people of European ancestry so it’s much easier to determine people are of European ancestry and harder to determine non-European ancestry. Results can be very broad like mine (Great Britain and Northwestern Europe) or as specific as regions within an individual country. “Accuracy is strongly affected by the choice of reference populations and the selection of genetic markers.” So caveat emptor; let the buyer beware.
The basics of this process involve three different testing techniques; one that determines maternal heritage, one paternal heritage, and one that pinpoints geographic region of origin. This is where it gets complicated. I’ll try to explain it simply.
Female origin is determined by analysis of mitochondrial DNA. Mitochondria are structures found in the cell nucleus (center) that contain their own DNA. Both males and females have mitochondrial DNA passed to them by their mothers. So testing this “provides information about the direct female ancestral line.” It tells you where your mother came from. Mitochondrial DNA testing is the technique used for maternal background information.
Y Chromosome testing gives information on paternal origin. Only males have a Y chromosome so this allows exploring ancestry “in the direct male line.” Paternal ancestry is determined by this testing technique.
Single Nucleotide Polymorphism testing evaluates large numbers of variables in a person’s entire genome. SNP’s are markers that determine ones geographic origin. The test counts the number of SNP’s the person has “from each geographic region….the percentage of an individual’s ancestry derived from each region can be estimated.” Thus you get the numbers in my report—71% here, 13% there, etc.
To summarize— Mitochondrial DNA provides info on one’s mother
Y chromosome testing provides info on one’s father
SNP testing determines info on one’s region of origin
The testing company also scans its database for others who match your DNA. It reports people they have recorded as having a similar DNA profile. The problem arises when testing yields surprise results. Examples of surprises are “lack of expected ancestry or the presence of unexpected ancestry. Discordance between pairs of siblings or between father and child can reveal nonpaternity.” Fortunately, this happens “in only 1% to 2% of births in Western populations” But that’s still a lot of people who get a surprise when their results are reported. One hears stories of people who learned they had children they didn’t know about. That would be a real shock. It also provides an avenue for adults adopted at birth to find one or both of their biological parents. That may be good or bad depending on the viewpoints of the individuals involved.
I don’t think the testing we did was anywhere sophisticated enough to determine that type of information. It didn’t tell me anything about my parents, but they are both deceased and no DNA is available for comparison. If someone is not in the company database, matches cannot be made. I learned only the general region of my origin. Like I said before, this was not new information.
There are “no clinical care guidelines regarding ancestry testing…it can be helpful for selecting the most appropriate genetic test (for genetic conditions)…and assessing risk for common diseases.” If it can be used for determining genetic risk for breast cancer, Alzheimer’s disease, polycystic kidney disease, cystic fibrosis and inborn errors of metabolism,” it is a very valuable tool, and one hopes that it can become the routine standard of care. Genetic testing for breast cancer has been done for many years and is a well-accepted practice. It’s not unusual for very high risk patients to have a preventive mastectomy. The accuracy of genetic testing for this disease has great utility and is life-saving.
Dr. G’s Opinion: The test I had was more a marketing gimmick than a revealing tool. The information I received was interesting, but it did nothing to give me helpful information I could use for improving longevity or avoiding serious illness. Those are far more complicated, expensive procedures that require special testing techniques. At my age the need for that is minimal.
References: Jorge LB, Bamshad MJ. Genetic Ancestry Testing What is it and why is it important? JAMA 2020 March 17;323(11):1089-1090.
https://www.ghr.nlm.nih.gov/primer/dtcgenetictesting/ancestrytesting
