Barr Bodies shown in female cells (XX) vs. the absence of Barr Bodies in male cells (XY)

A Barr Body is the completely inactive X chromosome in a female somatic cell to achieve dosage compensation.

Barr Bodies were discovered in 1948 by Murray Barr, a Canadian physician, and his graduate student, Ewart Bertram which studying the genetics of calico cats.

The process of inactivation is initiated from the X inactivation centre (Xic) near the centromere of the X chromosome. The Xic region contains 12 genes, two of which produce RNA sequences. Xist is a gene that produces one of the RNA sequences and plays an active role in chromatin restructuring of the X chromosome.