[R] anyone know how to calculate chi square value from P value?

[Anyuan Guo]

Dear all,
    I have P value of a list of markers. Now I need the chi square value 
with degrees of freedom 2.
    I noticed there are several Chisquare functions (dchisq, pchisq, 
qchisq, and rchisq), but it seems all are not for my purpose.
    In microsoft excel, there is a function CHINV to do this, such as 
CHINV(0.184, 2) is 3.386, that means the chi square value for P value 
0.184, degree 2 is 3.386.
    Does the R package has some function to do this?

Thanks

Anyuan