Barr Bodies and XISTence
September 3, 2009 5 Comments
Courtesy of my old biology textbook, a way in which we ladies are a special kind of parental battleground:
You have cells. In any one cell you’re expressing either your mom’s X chromosome or your dad’s. Not both. X-chromosome-wise, any cell on you is either all mom or all dad. You are a calico cat.* So, Mama X and Papa X have the same fight over and over in each one of your cells until one gives in and becomes inactive. This inactive X chromosome is called (I kid you not) a Barr body.
It gets better: a Barr body has to be inactivated by attaching methyl groups to cytosine, one of the DNA groups. The gene that seems to make that all happen is called XIST, which stands for X-inactive specific transcript. And which, said aloud, is EXIST.
*Literally: calico cats have orange and black patches because one parent’s X-chromosome won in the black bits and the other’s won in the orange bits. This is also why there are no male calicos.