dosage compensation by inactivation of X chromosome inactivation of paternal X chromosome by genomic imprinting https://github.com/geneontology/go-ontology/issues/22217 https://github.com/geneontology/go-ontology/issues/25955 GO:0060818 Imprinting controlled inactivation of the paternal X chromosome appears to be the ancestral form of sex chromosome inactivation in therian mammals. In eutherian mammals, imprinted X inactivation (iXCI) has largely been replaced by random X inactivation in a process regulated by the Xist and additional ncRNA's encoded within the "choice" region of the X chromosome. In a few mammals with early zygotic genome activation, imprinted X inactivation of the paternal X chromsome occurs very early during embryonic development. Imprinted iXCI has been observed in mice, rats, and bovines, and is best studied in mice where it occurs in the 4 cell stage in mice. In epiblast cells which will become the embryo proper, the inactivated paternal X chromosome is reactivated and dosage compensation of the X chromosome is regenerated by random X inactivation in embryonic tissues. In extraembryonic tissues, the selective inactivation of the paternal chromosome remains and is essential for proper development of the placenta. Selective inactivation of the paternal X chromosome via imprinting is the only form of X chromosome inactivation in marsupials, though the mechanism there may be significantly different in marsupials as the Xist transcript is not present on metatherian X chromosomes. inactivation of paternal X chromosome by genetic imprinting biological_process 2009-08-11T10:52:31Z iXCI Compensating for the two-fold variation in X-chromosome:autosome ratios between sexes by a global inactivation of all, or most of, the genes on the paternal X-chromosome in the XX sex by genomic imprinting. dph genomic imprinting