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The result is that the choice of inactivated X chromosome in all the cells of the organism is a random distribution, often with about half the cells having the paternal X chromosome inactivated and half with an inactivated maternal X chromosome; but commonly, X-inactivation is unevenly distributed across the cell lines within one organism ...
Barr bodies can be seen in neutrophils at the rim of the nucleus. In humans with more than one X chromosome, the number of Barr bodies visible at interphase is always one fewer than the total number of X chromosomes. For example, people with Klinefelter syndrome (47, XXY) have a single Barr body, and people with a 47, XXX karyotype have two ...
A 2013 study also found skewed X-inactivation to be a factor that predisposes individuals to esophageal carcinomas. [10] It has been postulated that skewed X-inactivation might lead to a decrease in the expression of X-linked tumor suppressor genes in an individual who also has a germline mutation in the expressed chromosome. This would cause ...
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 the past, the observation of the Barr body was common practice, as well. [47] To investigate the presence of a possible mosaicism, analysis of the karyotype using cells from the oral mucosa is performed. Physical characteristics of a Klinefelter syndrome can be tall stature, low body hair, and occasionally an enlargement of the breast.
The mosaic pattern of X inactivation may also determine how penetrant a disease is, if the disease allele is present on one X-chromosome and not the other. The organism may have few cells in which the diseased allele has not been condensed, leading to little expression of the disease allele. This is referred to as skewed X-chromosome inactivation.
Not all random X-inactivation is entirely random. Some alleles, generally mutations in the X-inactivation center on the X-chromosome have been demonstrated to confer a bias towards inactivation for the chromosome on which they sit. [1] Truly random X-inactivation may also appear to be non-random if one X-chromosome carries a deleterious mutation.
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]