How do companies like 23andMe figure so much stuff out just by a using a saliva sample?

Question

How do companies like 23andMe figure so much stuff out just by a using a saliva sample?

In: Biology

Answer 1

I think its to do with DNA and looking at patterns they already have seen. They must have a huge database of DNA now that they can compare and match certain attributes seen in your sample.

Or they just google you, and make some stuff up.