chromatin

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. SYN: heterochromatin.

- oxyphil c. SYN: 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 syndrome (XO) have none (sex c. negative), normal females and males with Klinefelter 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. SYN: Barr c. body.

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chro·ma·tin 'krō-mət-ən n a complex of a nucleic acid with basic proteins (as histone) in eukaryotic cells that is usu. dispersed in the interphase nucleus and condensed into chromosomes in mitosis and meiosis

chro·ma·tin·ic .krō-mə-'tin-ik adj

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n.

the material of a cell nucleus that stains with basic dyes and consists of DNA and protein: the substance of which the chromosomes are made. See euchromatin, heterochromatin.

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chro·ma·tin (kroґmə-tin) [Gr. chrōma color] the complex of nucleic acids (DNA and RNA) and proteins (primarily histones, but also nonhistone proteins) in the eukaryotic cell nucleus, comprising the chromosomes (q.v.). See also euchromatin and heterochromatin. chromatinic adj