How can scientists determine someone’s ethnicity based on their dna? Wouldn’t all the dna from different regions get all jumbled together pretty easily?
In: Biology
For a long time DNA didn’t get jumbled together because people couldn’t travel between different regions, or at least travel was slow and very rare.
This allowed certain genes to become common in some areas but not in others.
While genes *now* get frequently mixed together, if you find a gene in somebody’s DNA that used to be found only in Southeast Asia for example, you can infer that person has an ancestor from there.
It is not nearly as accurate as advertised, but can provide some information.
It’s important to note that these tests just compare your DNA to the company’s databanks of DNA samples with reported ethnicity. Most of these banks have a lot of data for caucasian groups (especially Western European) but are notoriously unreliable for other groups of people.
Also, keep in mind that various regions have different amounts of variability in their collective DNA sequences. For example, only a small subset of ancient humans left Africa to eventually reside in, say, the land that is now Scotland. So (before worldwide travel was easy/common) the ancient people in now-Scotland have a much more limited array of possible sequences than an equivalently-sized ancient population from now-Libya (for example) because the founding population is smaller.
The DNA tests are particularly good at showing specific relationships (e.g. paternity tests). But they are terrible at describing group relationships, since they just unreliably compare sequences to modern populations with self-reported ethnicity.
Lastly, just because your DNA test indicates that you have genetics similar to an ethnic group, it doesn’t mean that you then belong to that group. There are a lot of very good resources on this for white people who claim to belong to various Native American groups because of their DNA tests.
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