More Than a Pie Chart and a Number: Reading Your Ethnicity Estimate
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Remember when you got your ethnicity results? The anticipation, the excitement, the screen shot sent to friends and posted to Instagram? But did you ever stop to wonder where your estimate came from? And did you know there’s a lot more to it than a pie chart and percentages?
DNA is proof, right? So why do you call it an ethnicity estimate?
Creating an ethnicity estimate based on your DNA sample is a complex process based on probability, statistics, shared DNA, and ongoing research and science. AncestryDNA calculates your ethnicity estimate by comparing your DNA to a reference panel made up of thousands of people. Because reference panels and the way we analyze your DNA both change as we get more data, your ethnicity results can change as we get more data, too.
What’s a reference panel?
How does AncestryDNA decide if your DNA came from Ireland or Polynesia or Senegal or another region? First, our scientists create a reference panel by testing lots of people whose families have lived in one area for generations—Ireland, for example. Then they look for trends in their DNA results and compare those to other groups. Once they identify these trends for each region in the reference panel, they can look for them in your AncestryDNA test results.
Finding patterns that are distinct enough to tell one group from another is harder in places like Europe, where people have moved around and intermarried a lot. That’s why AncestryDNA continues to gather samples and improve its reference panel.
Here’s a simplified example of how AncestryDNA turns those trends into an ethnicity estimate. AncestryDNA looks at about 700,000 markers in your DNA sample. Those markers are called SNPs (pronounced snips). Each SNP refers to a certain position in human DNA. And each SNP is made up of a pair of letters representing some combination of A, T, C, or G. Let’s say that at SNP rs122 there are two possibilities: A and T. Because you get one letter (or allele) from each parent, you can have an AA, AT, or TT.
Each possible outcome at each SNP has a probability for how likely it is to show up in each region represented by the reference panel. We’ll pretend that rs122 occurs in three populations—Native American, Swedish, and English—at the following frequencies:
A = appears 5% of the time in Native American populations, 75% in English populations, and 80% in Swedish
T = appears 95% of the time in Native American populations, 25% in English populations, and 20% in Swedish
So, if you have AA at rs122, it seems you are more likely to be Swedish than Native American. If your DNA reads TT, the opposite seems more likely. One SNP doesn’t tell us much about your ethnicity, but when we apply the same process to thousands of SNPs, and then do the math, the grand total becomes the basis for your ethnicity estimate.
You Contain a Range of Possibilities
When you get your ethnicity estimate, the first thing you look for are the region names and percentages, right? But there are some other numbers that are just as important. Here’s an example of an AncestryDNA ethnicity estimate for someone with strong ties to northern Europe.
These results say that AncestryDNA estimates that 99% of this customer’s DNA comes from Europe. The next level includes Great Britain, Ireland, and Scandinavia. Each of these regions has a percentage and a range.
The percentages you get for regions in your ethnicity estimate are the most likely results we get after comparing your DNA to our reference panel. But they are not the only results. There are other possibilities that are nearly as likely. This is why we present your results as a range of possible percentages.
How do we determine that range?
In addition to the most likely estimate, our algorithm also generates 1,000 likely estimates using the probabilities learned from comparing your genetic data to our reference panel. We use these 1,000 likely estimates, which may be different from the most likely estimate, to figure out the range. The way we calculate the range will depend on the region and the value of the most likely estimate.
In the example above, as little as 14% and as much as 46% of this customer’s DNA appears to match the Ancestry Ireland reference panel, with an average percentage of 30%. That 30% is the most likely number within a range of percentages that are also likely. Less likely, but not necessarily by much. To find out your range of likely percentages, click on the ethnicity in your results that you are interested in.
These ranges are important to look at, especially for results with lower percentages. In these cases, the range can sometimes include zero. This means that for these results, it is possible that your ancestors didn’t live in that region or you didn’t inherit any DNA from ancestors who did.
But My Family Never Lived in [Your Mystery Region Here]
Our example estimate shows 30% Ireland. But what if you’ve never heard of anybody in the family
being from Ireland? This is where the maps and the polygons can help. By clicking on Ireland, the first thing that pops up is a note that this ethnicity is found primarily in Ireland, Scotland, and Wales. OK, so already there are new possible places the ancestor who passed this down might be from. Going from See Details to the Region History tab brings up a map with three colored, concentric polygons in and around Ireland. The smallest covers most of Ireland, but by the time you get to the outermost ring, you can see that DNA from this region is found throughout most of Great Britain as well.
The outer ring for the Great Britain region includes even more area: Germany, Switzerland, Denmark, France, bits of Norway, even Switzerland and Northern Italy. This all makes sense when you consider the migrations that took place more centuries ago, as Romans, Germanic tribes, Norsemen, and Norman French all made inroads into England. (You can read about those sorts of invasions and movements under the map on the Region History tab.)
So, your ethnicity estimate can provide insight not only on where your ancestors might have lived but also allow you to trace the path of your ancestors.
When Did All This Happen?
Your genetic ethnicity estimate tells you about your possible historical origins, not necessarily about where you live today. AncestryDNA genetic ethnicity estimates go back hundreds to more than a thousand years, when populations and their boundaries were often very different. This might lead to a different genetic ethnicity estimate than you might expect.
But while someone’s language, name, or culture may change when they move to a new location, their DNA doesn’t. This can lead to surprises in your genetic ethnicity. For instance, if the ancestors of your Italian ancestors migrated from Eastern Europe hundreds of years ago, you might show up as having Eastern European ethnicity instead of Italian.
The opposite can also happen. DNA is passed down randomly and the amount of DNA you might inherit from any particular ancestor decreases with each generation. That means you can have an ethnicity you know of in your family history that doesn’t show up in your ethnicity estimate.
If you haven’t looked at your ethnicity results in a while, go back and give them another look. You’re much more than a pie chart and a handful of percentages. And so is your AncestryDNA ethnicity estimate.