Solving the Mystery of the Evolution of X Chromosome Inactivation

Solving the Mystery of the Evolution of X Chromosome Inactivation

The X chromosomes of therian (marsupial and eutherian) mammals share a common evolutionary origin, with the marsupial X corresponding to approximately two-thirds of the human X chromosome. Inactivation of the X chromosome in female somatic cells is observed in both of these mammalian lineages and is presumed to have evolved in the therian ancestor to compensate for X-gene dosage differences between XY males and XX females. In the 50 years since Mary Lyon’s landmark publication on the hypothesis of X chromosome inactivation (XCI), we are still struggling to unravel the evolution of this fascinating silencing mechanism.