Supplementary Note 1

The MSY is flanked on both sides by pseudoautosomal regions, where X-Y crossing-over is a normal and frequent event in male meiosis1-4. 

1.            Cooke, H. J., Brown, W. R. & Rappold, G. A. Hypervariable telomeric sequences from the human sex chromosomes are pseudoautosomal. Nature 317, 687-692 (1985).

2.            Simmler, M. C. et al. Pseudoautosomal DNA sequences in the pairing region of the human sex chromosomes. Nature 317, 692-697 (1985).

3.         Freije, D., Helms, C., Watson, M. S. & Donis-Keller, H. Identification of a second pseudoautosomal region near the Xq and Yq telomeres. Science 258, 1784-1787 (1992).

4.         Li, L. & Hamer, D. H. Recombination and allelic association in the Xq/Yq homology region. Hum. Mol. Genet. 4, 2013-2016 (1995).