MEDICAL BIOLOGY, HUMAN ANATOMY, PHYSIOLOGY AND PATHOLOGY - Y.I. Fedoniuk 2010

BIOLOGY

SECTION 1. BIOLOGICAL FOUNDATIONS OF HUMAN VITAL ACTIVITY

1.3. MOLECULAR-GENETIC AND CELLULAR LEVELS OF LIFE ORGANIZATION

1.3.2. Structural, chemical and functional organization of eukaryotic cells

Sex Chromatin

X and Y sex chromatin are distinguished. X-chromatin (Barr body) was first discovered in 1949 by M. Barr and E. Bertram in feline Nerve Cells. The researchers noticed that it is present exclusively in female Cell nuclei, whereas male cells lack it. The Nature of the Barr body was established by M. Lyon (1961). X-chromatin (Barr body) represents one of the two X Chromosomes in females (mammals, humans) that undergoes heterochromatinization (tight Condensation) during early Embryogenesis and transitions into a genetically inactive state. Consequently, in a subset of cells, the maternal X chromosome is inactive, while in others, the paternal one is. This process of X chromosome heterochromatinization was named lyonization in honor of M. Lyon. The inactivation of one of the X chromosomes serves as a mechanism that balances sex chromosome Gene dosage between male (XY) and female (XX) cells. The determination of X-chromatin is used for the rapid Diagnosis of X chromosome copy number in the karyotype, which is essential for determining genetic sex at the Olympic Games, in forensic medicine and clinical practice, as well as for diagnosing hereditary disorders associated with sex chromosome numerical aberrations.

Y-chromatin (F-body) represents the Y chromosome in the somatic cell nuclei of males. The detection of X and Y sex chromatin forms part of the cytogenetic method.



Last update: 08/08/2026

Editorial and Educational Adaptation: This material has been compiled based on the primary/original source text. The project team performed an editorial review, corrected technical inaccuracies, structured sections, and adapted the content for an educational format.

What was processed:

  • elimination of formatting defects (OCR errors, structural breaks, corrupted characters);
  • editorial organization of content;
  • standardization of terminology in accordance with academic sources;
  • verification of factual statements against the original source text.

All mentions of the author, publication year, and origin of the primary text have been preserved in accordance with the source.