X inactivation, differentiation, and DNA methylation
Abstract
In this paper I attempt to explain mammalian X inactivation on the bases of DNA methylation and the properties of bacterial DNA methylases. Since most readers familiar with bacterial methylases may not be familiar with the X inactivation phenomenon, and vice versa, it was thought necessary to review briefly both areas before presenting new models.
The X inactivation phenomenon
Female mammals have two X chromosomes, whereas males have only one, creating a potential gene-dosage differential. In fact, however, this differential does not exist because a mechanism has evolved to maintain gene dosage effectively constant in both sexes. This mechanism, called X inactivation, results in one, and only one, active X chromosome per diploid autosomal set of chromosomes. Any additional X chromosomes are genetically inactive, heteropyknotic, and late replicating. The condensed, inactive X chromosome forms the sex chromatin, or Barr body...
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PDFDOI: http://dx.doi.org/10.1101/0.646-662