Physical mapping of the human pseudo‐autosomal region; comparison with genetic linkage map.

A long‐range restriction map of the pseudo‐autosomal or exchange pairing region (corresponding to the terminal parts of the short arms of the human sex chromosomes) has been established using pulsed field gel electrophoresis. A total of seven loci have been located on this physical map based essentially on the analysis of 45,X Turner genomes. The region spans a total of 2600 kb. The 5′ end of the MIC2 gene maps at less than 80 kb from the proximal pseudo‐autosomal boundary. Since the total pseudo‐autosomal linkage interval represents approximately 50% of recombination at male meiosis, 1 cM corresponds to 50‐60 kb. This is consistent with the almost 20‐fold increase in recombination frequency observed in male versus female meiosis in this region. The present data show no distortion between both physical and linkage maps. The distribution of the CpG‐rich restriction sites is notably disequilibrated. A large subset of these sites is concentrated within the 500 kb closest to the telomere whereas others appear in clusters (probably HTF islands) scattered in the rest of the pseudo‐autosomal region.