What are Barr bodies?

Barr bodies are specifically the inactive X chromosomes found in individuals who possess more than one X chromosome, typically females. In a typical female somatic cell, one of the two X chromosomes undergoes a process called X-inactivation, where it becomes largely transcriptionally inactive to balance the dosage of X-linked genes between males (who have one X chromosome) and females. This inactivated X chromosome can be visualized as a condensed, dark-staining structure within the nucleus and is referred to as a Barr body.

This mechanism helps prevent an overexpression of genes located on the X chromosomes, maintaining genetic equilibrium. In normal physiological circumstances, males do not have Barr bodies, as they only have one X chromosome; thus, there are no additional X chromosomes available to become inactivated.