Misconceptions of ancestry DNA tests- Part 2

Where do you come from? That’s a big question and not easily answered. As mentioned in the previous misconception post, ancestry DNA tests will identify specific regions from where you’ve inherited your DNA however it’s not so straight forward. One of the main issues is related to what kind of test you take and what that test can tell. The ancestry identification is based on autosomal DNA tests. Without delving too deep into the science, autosomal tests look at DNA that is inherited from both parents, and it will identify the region or regions from which you inherit your DNA. This in turn has its own flaws or limitations. To begin with it will only identify ancestry to a few hundred years back, perhaps as much as 1000 years at most, because the DNA of different groups changes over time due to migration and other factors. Essentially the test is comparing how similar your DNA is to modern populations in those regions, but as already stated, the DNA of those modern groups is not necessarily that of preceding populations especially the further back you go. The modern Italians are not ancient Romans, the modern Chinese are not the ancient Qins who built the Great Wall, nor are modern Guatemalans the ancient Maya. Modern populations may share some affinity to these groups but multiple human migrations and the rise and fall of empires have resulted in centuries and millennia of admixture of peoples and hence DNA.

For those who want to know their “deep” ancestry going back thousands of years, they will need a Y-chromosome or mitochondrial DNA test which follows the direct male and female lines of ancestry with which a haplogroup can be identified. Unfortunately as females lack a Y chromosome they can only do a mitochondrial DNA test. They would have to do a test of their father or brother to determine the details of their deep paternal ancestry.

It’s also important to note that because the tests only look at some markers on the DNA and not the whole sequence it is possible to get some false readings and this is why the “trace regions” that are sometimes identified appear suspect and may likely be incorrect. In some cases the primary regions could also be incorrect.

Another issue that is especially relevant for people of non-European origin is that some results are not correct or accurate due to small reference population size as the dataset is a bit Eurocentric. As mentioned earlier, the identification of ancestry regions is based on modern populations. Those places that have a larger reference population with which your DNA is compared to will provide a statistically more significant result (more accurate identification). If one of your ancestry groups has a very small reference population then your DNA from that region may appear less similar due to the small data set. The developed regions of the world generally have better data sets from the reference populations due to a number of factors.

The last issue worth mentioning again but in more detail is that the test may not be correct as it only looks at specific markers and not the whole DNA sequence. This means that different companies that are using different statistical analysis to analyze your DNA may produce different results on your ancestry due to what they are looking at in your DNA and what they are comparing it with and the quality and size of the data that they are comparing it with. DNA can’t tell the whole story which is why it is best to do genealogical research as well. Best of luck uncovering your own family’s history but please go forward with the right expectations. If you missed Part 1 then read it here.


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