A small condensed mass of the inactivated X-chromosome usually located just inside the nuclear membrane of theinterphase nucleus; the number of sex chromatin bodies per nucleus is one less than the number ofX-chromosomes,hence normal males and females with Turner's syndrome (XO) have none (sex chromatin negative), normal females andmales with Klinefelter's syndrome (XXY) have one, and (XXX) females have two chromatin masses. For technical reasonsonly about half the cells in a preparation show typical masses. Syn: sex chromatin.