chromatin (kro´ma-tin)

The genetic material of the nucleus, consisting of deoxyribonucleoprotein, which occurs in two forms during the phase between mitotic divisions: 1) as heterochromatin, seen as condensed, readily stainable clumps; 2) as euchromatin, dispersed lightly staining or nonstaining material. During mitotic division the c. condenses into chromosomes. [G. chroma, color]
heteropyknotic c. heterochromatin
oxyphil c. oxychromatin
sex c. a small condensed mass of the inactivated X-chromosome usually located just inside the nuclear membrane of the interphase nucleus; the number of sex c. bodies per nucleus is one less than the number of X-chromosomes, hence normal males and females with Turner's syndrome (XO) have none (sex c. negative), normal females and males with Klinefelter's syndrome (XXY) have one, and (XXX) females have two c. masses. For technical reasons only about half the cells in a preparation show typical masses. See also Lyon hypothesis.Barr chromatin body;


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