OnXinactivation inXOembryos of mammals

Abstract

SUMMARYBy analogy with the situation in coccids it is suggested that in mammalianXOembryos the singleXturns heterochromatic in some cells, but that such a change does not result in cell death because theXthen reverts back to an euchromatic and active state. This testable alternative to the Gartler–Sparkes hypothesis would imply that the anomalies of theXOTurner syndrome are largely due to imbalance of sex-linked genes rather than developmental damage resulting from cell death and that mammalianXinactivation might become reversed in response to special developmental needs.