Which sex chromosome is associated with X-inactivation and forms a Barr body in female mammals?

Which sex chromosome is associated with X-inactivation and forms a Barr body in female mammals?

• A. Y chromosome
• B. X chromosome
• C. Chromosome 21
• D. Mitochondrial DNA

Answer: (B)

In female mammals, one of the X chromosomes is silenced to balance gene expression with males who have only one X. The silenced X becomes highly condensed into heterochromatin and forms a Barr body at the edge of the nucleus. This inactivation is a classic example of dosage compensation and is driven by epigenetic marks that keep most genes on that chromosome from being expressed. So the chromosome involved in X-inactivation and forming a Barr body is the X chromosome. The Y chromosome isn’t inactivated to form Barr bodies, and chromosome 21 or mitochondrial DNA aren’t related to this process.

In female mammals, one of the X chromosomes is silenced to balance gene expression with males who have only one X. The silenced X becomes highly condensed into heterochromatin and forms a Barr body at the edge of the nucleus. This inactivation is a classic example of dosage compensation and is driven by epigenetic marks that keep most genes on that chromosome from being expressed. So the chromosome involved in X-inactivation and forming a Barr body is the X chromosome. The Y chromosome isn’t inactivated to form Barr bodies, and chromosome 21 or mitochondrial DNA aren’t related to this process.