BOB HIRSHON (host):
The when of the Y chromosome. I’m Bob Hirshon and this is Science Update.
For mammals like us, being biologically male is largely determined by having a Y chromosome. Now, for the first time, scientists have traced the Y chromosome’s origin. According to Diego Cortez of the Swiss Institute of Bioinformatics, sex-determining Y genes emerged separately in two different mammal lines, about 180 million years ago. What made them male and female before that is anyone’s guess.
DIEGO CORTEZ (Swiss Institute of Bioinformatics):
We actually don’t know the nature of the sex system in the ancestor of all mammals. That’s still an open question.
Possibilities include environmental factors like temperature, which influences sex in modern reptiles. Cortez says clues might be found in a few species of rodents, which actually lost the Y chromosome in their recent evolutionary past, and now develop into one sex or the other through a yet-to-be discovered mechanism. I’m Bob Hirshon for AAAS, the Science Society.