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Definition of X- and Y-chromatin
Last reviewed: 05.07.2025
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Determination of X and Y chromatin is often called a method of express diagnostics of sex. The cells of the oral mucosa, vaginal epithelium or hair follicle are examined. In the nuclei of female cells, there are two X chromosomes in the diploid set, one of which is completely inactivated (spiraled, tightly packed) already at the early stages of embryonic development and is visible as a lump of heterochromatin attached to the membrane of the nucleus. The inactivated X chromosome is called sex chromatin or Barr body. To detect sex X chromatin (Barr body) in the nuclei of cells, smears are stained with acetarcein and the preparations are examined using a conventional light microscope. Normally, one lump of X chromatin is found in women, and none in men.
To detect male Y-sex chromatin (F-body), smears are stained with acrichine and viewed using a fluorescent microscope. Y-chromatin is detected as a strongly luminous point, which differs in size and intensity of luminescence from other chromocenters. It is found in the nuclei of male cells.
The absence of a Barr body in women indicates a chromosomal disorder - Turner syndrome (karyotype 45, X0). The presence of a Barr body in men indicates Klinefelter syndrome (karyotype 47, XXY).
Determination of X- and Y-chromatin is a screening method; a final diagnosis of a chromosomal disease is made only after a karyotype examination.
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