It's well known that under the null hypothesis, the p-value has a uniform distribution. However, how can we determine the distribution for q-values (false Discovery Rate adjusted p-values)? I guess it is no longer uniform since the lowest is always increased. Thanks!
Under the null distribution, your true false discovery rate will always be equal to 100% (no matter what threshold you set, every hypothesis you accept will be a false discovery). Therefore, the true q-values will be nothing but a vector of 1's.
Of course, when q-values are estimated from the p-value distribution, they will not always be estimated as being exactly 1 (though they will generally be very high, perhaps
.9 or above). The exact distribution you end up with will depend on the method used to estimate q-values, and the number of hypotheses tested.