Question: How do websites like “Ancestry” find out where your family originated through your DNA?

Srinath Kasturirangan answered on 13 Mar 2019:

The answer is right there in your question!! It is through your DNA!! It is the DNA that you inherited from your parents (and your grandparents and your great grandparents) that decides the colour of your eyes or if you are going to be tall or short or if you are going to become bald! The makeup of your DNA can be influenced by where you live, what your ethnicity is, whether you have been exposed to certain environmental factors such as radiation etc. When you submit a sample of your saliva to Ancestry, they extract the DNA from it, break it up into small chunks and they compare these chunks to information in their database. Their database contains information on ethnicity / origins of DNA from 100s of 1000s of people that they have obtained through various means. So if a certain percentage of your DNA matches the DNA that is common to people of a certain ethnicity, they can use that to predict your ethnicity. Hope this made sense!