How is the X chromosome inactivated?
X-chromosome inactivation occurs randomly for one of the two X chromosomes in female cells during development. Inactivation occurs when RNA transcribed from the Xist gene on the X chromosome from which it is expressed spreads to coat the whole X chromosome.
What does X inactivation accomplish?
As nearly all female mammals have two X chromosomes, X-inactivation prevents them from having twice as many X chromosome gene products as males, who only possess a single copy of the X chromosome (see dosage compensation).
What are the consequences of X chromosome inactivation?
If an X-linked mutation results in the absence of a certain protein, a cell which has inactivated the wild-type, X-chromosome will experience problems from the protein absence, possibly resulting in growth disadvantage of that cell, or even cell death, which will result in selection against mutant cells.
What is the difference between Turner’s syndrome and inactivation of X chromosome?
What is the difference between Turner’s syndrome and inactivation of X chromosome? Women with Turner syndrome have just one X chromosome and normal women usually have only one active X chromosome because of the inactivation of one X-Chromosome (Barr body).
Do Turner syndrome females have Barr bodies?
The typical Turner’s syndrome patient, who has 45 chromosomes and only one sex chromosome (an X), has no Barr bodies and is, therefore, X-chromatin negative.
How many Barr bodies are in Turner woman?
0 Barr bodies
Answer: For Turner syndrome females, there will be 0 Barr bodies while for Klinefelter syndrome males, there will be 1 Barr body.
What is the purpose of X chromosome inactivation?
X-chromosome inactivation is the transcriptional silencing of one X chromosome in female mammalian cells that equalizes dosage of gene products from the X chromosome between XX females and XY males [1–3].
When does the X chromosome become inactive in the germline?
This inactivation event is irreversible during the lifetime of the individual, with the exception of the germline. In the female germline before meiotic entry, X-inactivation is reversed, so that after meiosis all haploid oocytes contain a single active X chromosome.
What causes the inactivation of the Xist gene?
Inactivation occurs when RNA transcribed from the Xist gene on the X chromosome from which it is expressed spreads to coat the whole X chromosome. In the first issue of Epigenetics and Chromatin, Nesterova and colleagues investigate the role of the RNA interference pathway enzyme Dicer in DNA methylation of the Xist promoter.
When does transcriptional silencing of the X chromosome occur?
Keywords. X-chromosome inactivation is the transcriptional silencing of one X chromosome in female mammalian cells that equalizes dosage of gene products from the X chromosome between XX females and XY males [ 1, 2, 3 ]. X-chromosome inactivation in the embryo proper occurs early in development.