How does the Xist gene make a Barr body?
Euchromatin is defined as the active form of chromosomal DNA whereas heterochromatin is defined as the inactive form of chromosomal DNA. Barr body is an inactivated X chromosome in females so as to compensate one X chromosome in males (dosage compensation). One X chromosome gets randomly inactive transcriptionally so that the gene expression of males and females is about the same.
Thus, Barr body is defined as the condensed, inactive member of a pair of X chromosomes in the cell. This process is known as Lyonization.
This inactivation process of X chromosome occurs due to chromatin condensation i.e. formation of heterochromatin. This can be carried out via three mechanisms: methylation of 5’ cysteine of DNA in X chromosome, presence of chromatin proteins that promote heterochromatization or by the cation of certain genes such as Xist.
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