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These changes help inactivate gene expression on the inactive X-chromosome and to bring about its compaction to form the Barr body. Reactivation of a Barr body is also possible, and has been seen in breast cancer patients. [12] One study showed that the frequency of Barr bodies in breast carcinoma were significantly lower than in healthy ...
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]
For example, Jiang et al. inserted a copy of the Xist gene into one copy of chromosome 21 in stem cells derived from an individual with trisomy 21 (Down syndrome). [50] The inserted Xist gene induces Barr body formation, triggers stable heterochromatin modifications, and silences most of the genes on the extra copy of chromosome 21.
The Barr body is indicated by the arrow. They are only present in cells with XX chromosomes. This was the evidence searched for in Barr body tests of samples from female athlete's inner cheeks. From 1958 to 1992, all female athletes underwent mandatory sex verification tests before taking part in any IAAF or IOC event.
Long non-coding RNAs, or lncRNAs, are RNA transcripts produced by RNA polymerase II that are not translated but participate in the regulation of gene expression. Long non-coding RNAs are used in various epigenetic processes in development, including the regulation of Hox genes, as well as in the creation of Barr bodies. [27] [28]
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.
The Barr body is indicated by the arrow, it identifies the inactive X (Xi). The X chromosome in humans spans more than 153 million base pairs (the building material of DNA ). It represents about 800 protein-coding genes compared to the Y chromosome containing about 107 protein-coding genes (42 exclusive protein-coding genes), [ 8 ] out of ...
An ortholog of the Xist RNA gene in humans has been identified in mice. [18] [19] This ortholog encodes a 15 kb Xist transcript that is also localized in the nucleus. However, the ortholog does not feature conserved repeats. [20] The Xist RNA gene is located within the Xist Inactivation Center (XIC), which plays a major role in X-inactivation. [21]