Here's the breakdown:

* Females have two X chromosomes (XX), while males have one X and one Y (XY).

* X-inactivation is a process that occurs early in female embryonic development. It ensures that females don't have twice the amount of X-linked gene products as males.

* One of the two X chromosomes in each female cell is randomly inactivated. This means that the genes on that chromosome are silenced.

* The inactivated X chromosome condenses into a compact structure called a Barr body. This dense structure is visible under a microscope.

* The inactivation is random, meaning that in different cells of a female's body, either the maternal or paternal X chromosome can be inactivated. This leads to a mosaic expression of X-linked genes in different tissues.

Therefore, the presence of a Barr body is a characteristic feature of female mammalian cells and indicates the presence of an inactive X chromosome.