Department of Vertebrate Genomics, Max Planck Institute for Molecular Genetics, Berlin, Germany. zerck@molgen.mpg.de|Department of Vertebrate Genomics, Max Planck Institute for Molecular Genetics, Berlin, Germany. zerck@molgen.mpg.de|Department of Vertebrate Genomics, Max Planck Institute for Molecular Genetics, Berlin, Germany. zerck@molgen.mpg.de|Department of Vertebrate Genomics, Max Planck Institute for Molecular Genetics, Berlin, Germany. zerck@molgen.mpg.de