The cloning of the 'testis determining gene', SRY, promised a revoluti
on in the understanding of sex determination in humans. The failure to
isolate further genes involved in sex determination has been a disapp
ointment. The biology of SRY, however, has kept the field exciting. Th
e discoveries of sex reversing SRY mutations with variable penetrance,
but with full expressivity, rapid SRY sequence evolution and circular
Sry transcripts could not have been predicted.