What does the formation of a barr body inactivate?
1 Answer
A barr body is an inactivated X-chromosome in female somatic cells.
Explanation:
Female somatic cells have two X-chromosomes. To keep the expression of the genes on X-chromoses within acceptable levels, one X-chromosome is normally inactivated (dosage compensation). An inactivated X-chromosome appears as barr body, it is a very condensed form of the inactive X chromosome, seen in nucleus of female somatic cell.
The transcriptional silencing of an X-chromosome is executed in a highly coordinated manner, early in the development of an embryo. It only occurs in somatic cells, not in sex cells.
Which X-chromosome is silenced/ inactivated is completely random except in the process of imprinted X-inactivation. In the latter case the paternal X-chromosome is silenced; this process is not completely understood yet and a subject of research.
Once the X-chromosome is silenced in somatic cells it remains silenced in all descendant cells.
The phenomenon of random X-inactivation can be observed in the fur of tortoiseshell cats that are heterozygous for the X-linked gene that determines fur color (see image).
