In mammals, embryos are considered to be sexually indifferent until the action of a sex-determining gene initiates gonadal differentiation. Here it is demonstrated that this situation is different for birds. Using rare, naturally occurring chimaeric chickens where one side of the animal appears male and the other female, it is shown that avian somatic cells possess an inherent sex identity and that, in birds, sexual differentiation is cell autonomous.
- D. Zhao
- D. McBride
- M. Clinton