highly significantP < 1 × 10 −5
The mean synonymous site nucleotide diversity ( π syn ) for X-linked genes (Tables 1 and 2 ; Additional file 1 : Table S4) is 0.00017, versus 0.0018 for all autosomal genes identified; the mean estimated nucleotide diversity for all sites ( π ) is 0.00038 for the X-linked region, again much lower than values for the autosomal region or PAR (0.0017 and 0.0020, respectively, which do not differ significantly (Wilcoxon rank sum P = 0.12), while the difference from the X-linked region is highly significant ( P < 1 × 10 −5 ) for both regions).