Sex Chromatin

(redirected from paranucleolus)
Also found in: Dictionary, Thesaurus, Medical.

sex chromatin

[′seks ′krō·mə·tən]
(cell and molecular biology)

Sex Chromatin


a solid stained body found in the nondi-viding interphasic nuclei of cells in heterogamous (having X and Y sex chromosomes) animals and in man. There are two types of sex chromatin: the X chromatin, or Barr body, discovered in 1949 by the British researchers M. Barr and E. G. Bertram, and the Y chromatin, discovered in 1970 by the Swedish scientists T. Caspersson and L. Zech.

The chromatin is a body that is intensively stained by basic dyes (0.7–1.2 micrometers) and usually found adjacent to the nuclear membrane. It has a triangular, crescent, or round shape. The Y chromatin is much smaller and is visible when the nucleus is stained by fluorochromes, such as quinacrine hydrochloride or quinacrine yperite, and examined under ultraviolet light. In individuals of the female sex (XX type), one of the X chromosomes is inactive. This is shown by its greater spiralization and consolidation. The spiraled X chromosome is also visible in an interphasic nucleus in the form of X chromatin. The Y chromosome in man and some primates has a large heterochromatin area which is strongly fluorescent.

A technically simple examination of an interphasic nucleus reveals the condition of the system of sex chromosomes. The X chromatin is found more or less frequently in women in the nuclei of all tissue cells, for example, in 15–60 percent of the nuclei in the epithelial cells of the oral mucous membrane. The number of nuclei with X chromatin depends on the rate of cell reproduction in a given tissue and on the hormonal state of the organism. A change in the quantity of sex chromatin shows that there has been a change in the number of sex chromosomes. This can be ascertained in more detail by analyzing the karyotype. Sex chromatin is widely used to determine the sex of an unborn child. This is necessary in those cases where there is a possibility of inheriting sex-linked diseases.


Zakharov, A. F. “Novye metody analiza khromosom cheloveka.” In Itogi nauki i tekhnika: Seriia “Genetika cheloveka,” vol. 1. Moscow, 1973.
“Fluorescent Staining of Heteropycnotic Chromosome Regions in Human Interphase Nuclei.” Experimental Cell Research, 1970, vol. 61, nos. 2–3.
The Sex Chromatin. Edited by K. L. Moore. Philadelphia-London, 1966.