Direct sizing of the pseudoautosomal region (PAR). (A) Schematic representation of the genomic structure of the Fxygene, indicating the position of the pseudoautosomal boundary (PAB) and the integrated I-SceI site. Exons are indicated by roman numerals, and the initiation and termination codons (ATG and TGA, respectively) are shown. (B) Southern analysis of the size of the PAR in 129 mice. Wild-type embryonic stem cell (ES) and targeted embryonic stem cell (Targeted) genomic DNA was incubated with (+) or without (−) the restriction enzyme I-SceI and were hybridized to the pseudoautosomal probes Mov15 or Fxy3. Size, estimated from molecular weight markers (Hansenula wingeichromosomes), is indicated on the right.