Here are some reasons why your percentage for an ancestral region might be higher or lower than you expected:
Neighboring regions often share DNA
Over the last thousand years, there have been times when some groups of people were isolated from other populations. Isolation gives populations a chance to develop a unique genetic signature.
When individuals from previously separated populations have children together, they share DNA in what we call admixture. As populations admix, they become more difficult to tell apart using genetics. If your family comes from a population with a history of admixture, your percentages for some regions may be different than you expect.
Populations living near geographic borders are often admixed—sometimes to a large degree. For example: we find that even people with deep family roots in Portugal still have about 12% of their DNA that matches most closely to people in our reference panel with deep family roots in Spain.
This is likely due to Spain and Portugal being close neighbors with centuries of trade and migration between them. This means that even if both your parents are from Portugal, you will likely not get 100% Portugal, but instead might get some Spain as well.
As we continue to improve our methods of analysis and increase the size of the reference panel we compare your DNA to, we should be able to provide more precise results and better tell nearby regions apart. More sensitive tools may also mean we discover more instances of admixture between neighboring populations.
Ancestral regions include a predicted range
The percentage you get for a region is the most likely result we get after comparing your DNA to our reference panel. But it is not the only possible result. There are other percentages that are also likely. That’s why, in addition to your most likely result, we also provide a range of other possible percentages.
In this example, our results show that 7% of this person’s DNA looks most like DNA from people in Senegal. Additionally, we show that this percentage could range from 7% to 10%.
Essentially, 7% is the most likely result, but your actual percentage for the region may be somewhat higher or lower than that. If you find that your percentage for a region doesn’t match what you expect, remember that your actual percentage could fall somewhere in the range.
Importantly, the range of percentages can also include 0%. In these cases, even if you’re assigned a very small percentage to an ancestral region, it’s possible you may not actually share any DNA with this region. (Read more about how we determine the range of percentages.)
DNA inheritance is random
A child inherits half of each parent’s DNA. Which DNA the child receives from each parent, however, is random. For example, if a parent is 50% Ashkenazi Jew and 50% German, a child will not necessarily inherit equal amounts of each region from that parent. The child may inherit slightly more or less of one or the other region.
If you have siblings, you’ll all get a different mix of DNA from your parents (unless you’re an identical twin). So you’ll likely have different results than your siblings because of the random way pieces of DNA are inherited. (Read more about the random inheritance of DNA.)
Here's another example. If you have a great-great-grandparent with Native American ancestry, you might expect to have 1/16th (about 6%) Indigenous Americas—North. However, the pieces of DNA that you inherited from this great-great-grandparent are random. When the DNA was passed from your great-great-grandparent to your great-grandparent to your grandparent to your parent and then to you, some pieces of DNA from this great-great-grandparent were not passed on.
Since you might not have much DNA from that great-great-grandparent, you might not show any Indigenous Americas—North.
This doesn’t prove that you don’t have any Native American ancestors or heritage. It just means that you didn’t inherit the genetic markers AncestryDNA uses to connect you to Indigenous Americas regions. (Read more about Indigenous Americas Regions.)
So keep in mind the random nature of DNA inheritance, especially if you don't have exactly the ancestral regions you expected. (To learn more about how DNA is inherited, read Understanding Inheritance.)
Inferring ancestral regions is a complex problem
Another thing to keep in mind is that inferring ancestral regions through DNA is a science that researchers around the world are continuing to develop. At AncestryDNA, we are on the cutting edge of this science, and we do our best to give you the best possible results. However, the fact is that inferring ancestral regions is challenging (though we love that challenge).
Human history is complex, with lots of populations and cultures mixing together through centuries of migration, trade, marriage, war, and more. This makes assigning ONE region to each person nearly impossible. But it also means there is so much for you to discover by looking at your genetic ancestry.
You can be confident that we are giving you the best results possible given our current data and knowledge of human genetics. However, you can also be sure that we are working hard to continue to improve the precision of your results as scientists unlock even more of the mysteries within the human genome.
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