: Why can’t DNA tests and Genetics determine race & ethnicity when it can tell you where your ancestors are from, and if not what does?
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A lot of responses have touched on the societal reasons it is impossible to empirically determine race or ethnicity from DNA so I thought I would also touch on how the science works and how ancestry results can be misleading.
The ancestry percentages that you receive from a test like 23andMe are not a percent out of 100. If your results say that you have “60% European ancestry” they aren’t saying that 60% of your DNA is European. They are calculating the likelihood that your genome came from a specific region. So the percentages are actually saying “there is a 60% chance that your genome comes from Europe”.
To calculate these percentages they look at specific regions of the genome that are known to have variation between people (99.9% of you DNA is the same as everyone else so there are relatively few places where variation occurs). For instance, a specific location in your DNA might read A – **T** – **C** and mine might read A – **T** – **A.** It might just so happen that having a **T** in the second spot is more common in people from Europe and having a **C** in the 3rd spot is more common in people from Asia. So 23andMe would say that your ancestry is 50% European and 50% Asian. That does not mean that you are half European and half Asian, it means that there is a 50/50 likelihood that your DNA is European OR Asian (the actual math is way more complicated, if interested look up [Random Match Probability](https://dnaconsultants.com/random-match-probability/) and [likelihood ratios](https://www.forensicmag.com/3425-Featured-Article-List/576342-How-to-Use-the-Likelihood-Ratio/)).
This is similar to how DNA “matches” are calculated in a forensic setting.
Source: am Forensic Biologist
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