system
Given the following post, respond as if you're commenting on Reddit:
human
Are doppelgängers genetically similar to their look-a-like?

We all have met people who could be sibling because they have the same build, colouring, even mannerisms yet they are not related. Could there be a relation several generations back that they are not aware of or is this just an anomaly? Would this show up genetically?
gpt
To demonstrate that doppelgangers have genetic similarities would require a large study for a few reasons.

1. We have a massive amount of unexpressed information in our genes and we can't (at the moment) just narrow it down to the genes responsible for our appearance.
2. We would need a large amount of people to participate in this study to achieve a result that is statistically significant (if indeed there is one).
3. Doppelgangers are not (in reality) exact copies, so to perform a study to answer your question, there would need to be a large amount of facial/body analysis to determine how similar two people look... doing that would probably result in the generation of new units of measurement.

I don't believe anyone can answer your question at the moment, sorry.
To answer the opposite question: how often are people with different appearances genetically similar?

I was going to say that individuals from different races can be more genetically-similar to each other than to members of their own race, but that information has been re-examined and is very likely untrue. 
Currently, it appears that two individuals of the same race are more similar to each other than to individuals of a different race (Witherspoon et al. Genetic Similarities Within and Between Human Populations. 2007).