**2.3k**wrote:

Hello,

I am interested in traces of positive selection in my population data. I have been able to calculate Watterson's Pi and Theta for synonymous and non-synonymous sites for every gene in my genome.

The problem is that I am a bit lost as to how to look for positive/negative selection. I do not really understand what these values are, Pi and Theta. I have seen literature where Pi(A) is divided by Pi(S), that's sort of like dN/dS, and if the ratio is bigger than 1, then we can infer positive selection?

Thanks for any help,

Adrian

**230**• written 4.9 years ago by Adrian Pelin •

**2.3k**