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A Barr body (named after discoverer Murray Barr) [1] or X-chromatin is an inactive X chromosome. In species with XY sex-determination (including humans), females typically have two X chromosomes, [ 2 ] and one is rendered inactive in a process called lyonization .
The Barr body is indicated by the arrow, it identifies the inactive X (Xi). ... X-inactivation (also called Lyonization, after English geneticist Mary Lyon) ...
Ohno's studies of Barr bodies in female mammals with multiple X chromosomes revealed that such females used Barr bodies to inactivate all but one of their X chromosomes. Thus, Ohno described the "n-1" rule to predict the number of Barr bodies in a female with n number of X chromosomes in her karyotype. [6]
X chromosome reactivation (XCR) is the process by which the inactive X chromosome (the Xi) is re-activated in the cells of eutherian female mammals. Therian female mammalian cells have two X chromosomes, while males have only one, requiring X-chromosome inactivation (XCI) for sex-chromosome dosage compensation. In eutherians, XCI is the random ...
In female humans, Barr bodies are defined as the condensed and inactivated X-chromosome that is found in every cell of the adult. Because females have two nearly identical X chromosomes, one of them must be silenced so that the expression levels of the genes on the X-chromosome are of the proper dosage.
n/a Ensembl ENSG00000270641 n/a UniProt n a n/a RefSeq (mRNA) n/a n/a RefSeq (protein) n/a n/a Location (UCSC) Chr X: 73.79 – 73.83 Mb n/a PubMed search n/a Wikidata View/Edit Human Simplified flowchart of Tsix's role in Xist gene function Tsix is a non-coding RNA gene that is antisense to the Xist RNA. Tsix binds Xist during X chromosome inactivation. The name Tsix comes from the reverse of ...
This phenomenon is called X-inactivation or Lyonization, and creates a Barr body. If X-inactivation in the somatic cell meant a complete de-functionalizing of one of the X-chromosomes, it would ensure that females, like males, had only one functional copy of the X chromosome in each somatic cell. This was previously assumed to be the case.
Xist (X-inactive specific transcript) is a non-coding RNA transcribed from the X chromosome of the placental mammals that acts as a major effector of the X-inactivation process. [5] It is a component of the Xic – X-chromosome inactivation centre [6] – along with two other RNA genes (Jpx and Ftx) and two protein genes (Tsx and Cnbp2). [7]