A Barr body (named after discoverer Murray Barr) or X-chromatin is an inactive X chromosome. In species with XY sex-determination (including humans), females typically have two X chromosomes, and one is rendered inactive in a process called lyonization. Errors in chromosome separation can also result in male and female individuals with extra X chromosomes. The Lyon hypothesis states that in cells with multiple X chromosomes, all but one are inactivated early in embryonic development in mammals.Brown, C.J., Robinson, W.P., (1997), XIST Expression and X-Chromosome Inactivation in Human Preimplantation Embryos Am. J. Hum. Genet. 61, 5–8 (Full Text PDF) The X chromosomes that become inactivated are chosen randomly, except in marsupials and in some extra-embryonic tissues of some placental mammals, in which the X chromosome from the sperm is always deactivated.
A Barr body (named after discoverer Murray Barr) or X-chromatin is an inactive X chromosome. In species with XY sex-determi.nation (including humans), females typically have two X chromosomes, and one is rendered inactive in a process called lyonization Errors in chromosome separation can also result in male and female individuals with extra X chromosomes The Lyon hypothesis states that in cells with multiple X chromosomes, all but one are inactivated early in embryonic development in mammalsBrown, C.J., Robinson, W.P., (1997), XIST Expression and X-Chromosome Inactivation in Human Preimplantation E,mbryos Am. J. Hum. Genet. 61 5–8 (Full Text PDF) The X chromosomes that become inactivated are chosen randomly, except in marsupials and in some extra-embryonic tissues of some placental mammals, in which the X chromosome from the sperm is always deactivated.