We take the \(1-\alpha\) quantiles of the individual LOD
scores.
In the case of X-chr-specific permutations, we use the combined length
of the autosomes, \(L_A\), and the length of the X chromosome,
\(L_X\), and calculate the area of the A:A, A:X, and X:X regions as
\(L_A^2/2\), \(L_A L_X\), and \(L_X^2/2\), and then use the
nominal significance levels of \(1 - (1-\alpha)^p\),
where \(p\) is the proportional area for that region.