The 23andMe Ancestry Algorithm Gets an Upgrade

Improved accuracy. Less uncertainty. Better science.

We like to call 23andMe’s Ancestry Composition a living analysis of your DNA, one that gets better and more granular over time as more and more people from different backgrounds become customers. 

This Fall we’re making another upgrade to that analysis that will improve the accuracy, as well as reduce the amount of “unassigned” and non-specific ancestry assignments. But, some 23andMe users may see some pretty big shifts in their results: For example, many should expect an increase in their most common ancestry proportion and a reduction in their broadly ancestries. The end of this post includes a summary of some of the most common ways in which 23andMe users’ results will change. 

In parallel with this update to the Ancestry Composition analysis, we’re updating our reference dataset for our recent ancestor locations feature, so you might see your recent ancestor locations and match strengths change as well.  

This is all part of our ongoing efforts to improve our customer offerings. It’s worth looking back at what we’ve done since 2008 when we first started offering customers a breakdown of their ancestry. 

A look back

A lot has happened in the past 12 years. Millions of individuals have joined 23andMe and ongoing research efforts have helped us understand more about genetic diversity around the world. 23andMe has also made great strides in improving the underlying algorithms and reference populations that we use to deliver these results. In 2008, we broke down ancestry into three main categories: African, European, and East Asian. Since then we’ve offered a series of updates where we refined those original estimates into more and more granular results. Now customers can discover if their DNA traces to more than 2,000 regions worldwide.

When we update the algorithms or the reference populations used to predict your ancestry, your results are expected to change. That’s why we call Ancestry Composition a living analysis of your DNA. For the most part, these changes should be minor and hopefully provide you with more detail about your ancestral origins. Like almost everything we do, these changes are based on science, and we want to be transparent about what we’re doing. That’s why each time we make an update, we share it in our “Change Log”, which can be found at the bottom of the Scientific Details section of your Ancestry Composition report. If you want even more detail, you can look at our Ancestry Composition Guide, or for those with a science bent, check out our White Paper.

More about the most recent update to Ancestry Composition 

Since 2014, 23andMe has added or expanded dozens of reference populations, but the core Ancestry Composition algorithm has remained almost completely unchanged. Until now. 

In 2020, our R&D team developed a new approach that dramatically improves accuracy, while reducing both unassigned and nonspecific ancestry.

To understand what’s changing, let’s first review the basics.  

A simple, step-by-step guide to Ancestry Composition

Step 1: Assigning

First, we just separate the customer’s genome data into little segments, like boxcars on a train. Each boxcar only contains the data for about 300 DNA markers — out of a total of over 650,000 that we test for on our genotyping chip. And dividing 650,000 by 300 DNA markers, you get about 2,000 boxcars. 

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