[eli5] Are DNA tests actually able to accurately determine ancestry, and, if so, how?

Question

[eli5] Are DNA tests actually able to accurately determine ancestry, and, if so, how?

In: Biology

Answer 1

They work by comparing the DNA of the subject to the DNA of people whose ancestry they already know.

So they are limited by the people they start with (and how accurate their ancestry information is).

This tends to mean that the commercial DNA-ancestry services are fairly good at specific ancestry groups or ethnicities (i.e. people with at most a few generations of ancestry in North America, and then more in Western Europe), but tend to be pretty unreliable for anything outside those groups.

Answer 2

Determine: Yes

Accurately: No

The companies choose markers which are common in the “ancestry” groups which they are marketing. They are just tell?ng you what percentage of those markers you have.