A little more on sex determination:
Not so clear-cut as X and Y:
- The presence of other genes, located on the X, Y and other chromosomes, influence the determination of embryonic sex.
The SRY gene:
- Normally present on the Y chromosome
- Induces the sexless embryonic gonad to develop into a testis
- Can sometimes be present on the X chromosome, leading a genetic female (XX) to develop testis
- 1990: a fertilized mouse embryo with the XX configuration was injected with SRY and developed as a male both anatomically and behaviorally.
- (Andrew Sinclair, Center for Hormone Research, University of Melbourne)