sex chromatin

All human cells, says Dr. Murray L. Barr of the University of Western Ontario, contain something called sex chromatin.

The cells were then examined for the presence of sex chromatin, a substance found only in female cells.

Later research showed that the spots, now known as "Barr bodies" or sex chromatin, consisted of one X chromosome � the one that is inactivated after it has done its job of helping to determine femaleness.