A mean-field version of the Nicodemi-Prisco SSB model for X-chromosome   inactivation
  Nicodemi and Prisco recently proposed a model for X-chromosome inactivation in mammals, explaining this phenomenon in terms of a spontaneous symmetry-breaking mechanism [{\it Phys. Rev. Lett.} 99 (2007), 108104]. Here we provide a mean-field version of their model. 
G. Gaeta