Monday, June 19, 2006

Why do we Xist?

There are a number of ways for animals to determine the sex. In mammals it usually involves having an XX or a XY. To compensate for gene dosing of 2 Xs versus one X in the male, the small non-coding Xist RNA inactivates one X (of McBurney fame). An article in Science takes a stab at its evolution. Xist evolved, at least partly, from a protein-coding gene and that the loss of protein-coding function of the proto-Xist coincides with the four flanking protein genes becoming pseudogenes. This event occurred after the divergence between eutherians and marsupials, which suggests that mechanisms of dosage compensation have evolved independently in both lineages.