Talk:XO sex-determination system

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How does it work?

As I understand it, in the XY system the Y contains both the sex-determination allele and a bunch of stuff only useful to males. In the case of XX, one turns off the other to prevent double expression.

So how does this transition to an X / XX system? How do males get by without the aforementioned useful stuff? How do males know they're male when the sex-determination is absent? Since one X would turn the other off, how do females know they have a second X?

Is the transition from XY to X0 universally possible, or are there limits set by anatomy, physiology, Y or X chromosome structure, or other factors? — Preceding unsigned comment added by 82.139.81.0 (talk) 23:40, 27 November 2012 (UTC)[reply]