Does X-inactivation result in a Barr body?
In X-inactivation, an X chromosome is compacted (or, as my intro bio professor liked to say, “crumpled up into a ball”), to make a small, dense structure called a Barr body. Most of the genes on the Barr body are inactive, meaning that they are not transcribed.
What causes skewed X-inactivation?
It can be caused by primary nonrandom inactivation, either by chance due to a small cell pool or directed by genes, or by secondary nonrandom inactivation, which occurs by selection. X-chromosome inactivation occurs in females to provide dosage compensation between the sexes.
How is X chromosome inactivated and reactivated?
X chromosome inactivation is initiated in early embryos by the noncoding Xist RNA. Subsequent chromatin modifications on the inactive X chromosome (Xi) lead to a remarkable stability of gene repression in somatic cell lineages.
Does methylation cause X-inactivation?
DNA methylation plays a key role in X-chromosome inactivation (XCI), a process that achieves dosage compensation for X-encoded gene products between mammalian female and male cells.
Are Barr bodies completely inactive?
The Barr, or sex chromatin, body is an inactive X chromosome. It appears as a dense, dark-staining spot at the periphery of the nucleus of each somatic cell in the human female.
Can a Barr body be reactivated?
Reactivation of a Barr body is also possible, and has been seen in breast cancer patients. One study showed that the frequency of Barr bodies in breast carcinoma were significantly lower than in healthy controls, indicating reactivation of these once inactivated X chromosomes.
Can Barr bodies be reactivated?
Why Barr body is inactive?
A Barr body (named after discoverer Murray Barr) or X-chromatin is an inactive X chromosome in a cell with more than one X chromosome, rendered inactive in a process called lyonization, in species with XY sex-determination (including humans). Barr bodies can be seen in neutrophils at the rim of the nucleus.
Are Barr bodies permanent?
A Barr Body is an inactivated, condensed X chromosome found in female cells. Since females possess two X chromosomes and males have one X chromosome and a Y chromosomes, Barr bodies are essential to regulate the amount of X-linked gene product being transcribed.
What is relationship between heterochromatin and Barr body?
Heterochromatin protein-1 is a component of the Barr body Once established, the heterochromatic state of the mammalian inactive X chromosome must be maintained to prevent reactivation of X-linked gene expression.
What does the presence of Barr body indicate?
Inactivated X chromosomes seen in female somatic cells are called Barr-bodies which are present adjacent to the nuclear membrane. Condensed state of densely stained chromatin signifies that in such cases DNA replication occurred at the later stage of S phase of cell cycle.
Why is heterochromatin inactive?
Transcriptionally inactive heterochromatin is vital to sustaining stable chromosome structure throughout the cell cycle. Heterochromatin is densely packed and inaccessible to transcription factors so it is rendered transcriptionally silent (Richards and Elgin 2002).