**120**wrote:

I am trying to grasp what Fu's Fs intuitively means.

Kent Holsinger's Population genetics notes states "S is the probability of observing a random sample with a number of alleles equal to or smaller than the observed value under given the observed level of diversity and the

assumption that all of the alleles are selectively neutral"

From what I tried to gather -

Does this mean S is the probability of observing the entire range of haplotypes in any random selection of haplotypes from the sample ? In such a case, Fu's Fs = ln(S/1-S) would be negative (suggesting negative or purifying selection) for S<0.5. A low value of S suggests that there are many haplotypes in the dataset (not what I would expect from negative selection, which results in ideally one dominant haplotype and a few rare variant haplotypes), and so the probability of getting them all in a random selection is low.

I could be completely off in my understanding, could anyone please guide me here ?