At an early stage in a female embryo’s development, one of the two X chromosomes in each of its cells becomes inactivated. In two recent papers, the lab of Jeannie Lee makes important breakthroughs in uncovering how the two X chromosomes decide their fate.

A study in the Jan. 20, 2006 Science shows that the chromosomes literally get together before one of them bows out.

The other, in the March 3, 2006 Molecular Cell, sheds light on the inactivating mechanism, how an RNA called Xist gets switched on in order to envelop the future inactive chromosome.