Cheek cells showing a Barr Bodies. In mammals, males are heterogametic XY, and females homogametic XX. Females' cells have twice the X chromosomes of a male cell, except that one of the X chromosomes is "turned off," and appears as a darkly staining body attached to the nuclear membrane inside the nuclei of somatic cells. Now called Barr bodies, it is a simple way to detect whether a cell is from a male or a female. Magnification 400x @ 35MM.