Sex chromatin

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The nucleus of a human, female fibroblast was stained with the blue fluorescent DNA dye DAPI in order to represent the Barr body, i.e. the inactive X chromosome (arrow). In addition, a special form of a histone (macroH2A) with antibodies coupled to a green fluorescent dye was detected in the same nucleus . This special histone form is enriched in the Barr body.
Nucleus of a female human cell made from amniotic fluid . Above: Both X chromosomes are shown by fluorescence in situ hybridization . A single optical section is shown, which was produced with a confocal laser scanning microscope . Below: the same core with DAPI staining, recorded with a CCD camera . The Barr body can be clearly seen here (arrow) and identifies the inactive X chromosome (Xi).

As sex chromatin (also: Barr body) or sex chromatin is chromatin structures in the cell nucleus called, that can be detected with dyes, and are found only in one sex. They are caused by sex chromosomes . In humans, the term includes the Barr body and the F body .

F-body

The F-body (from English fluorescence body , 'fluorescent body', sometimes also 'F-body') occurs in male cells. It is the Y chromosome , which contains a lot of heterochromatin and is sometimes detectable because of the better staining that is associated with it.

Barr bodies

See also: X inactivation

The Barr body occurs in women. It is a largely inactive X chromosome that is heterochromatinized and thus becomes detectable ( X inactivation ). Women usually have two X chromosomes, one of which is inactivated and can then be found in many cells as Barr bodies. In addition to the Y chromosome, men only have one X chromosome and therefore no Barr body. Although an inactive X chromosome is present in all normal female cells, a Barr body cannot be detected equally well in all cell types and cell cycle stages.

It was first described in 1949 by Murray Llewellyn Barr and Edward George Bertram , without initially knowing the causes. In the early 1960s, Mary Frances Lyon published the Lyon hypothesis, later named after her, that one of the X chromosomes in every cell is inactivated and when this happens (around the 16th day of human embryogenesis). She also coined the term Barr body , in German Barr body or Barr body.

If no Barr body is found in a woman, it can either be that an X and a Y chromosome are present as in men, but that the “masculinity” gene has been lost on the Y chromosome . Or the woman only has one X chromosome (genotype X0; Turner syndrome ). If a woman has more than one Barr body, one speaks of triplo-X syndrome or poly-X syndrome . However, there are also men with one or more Barr bodies ( Klinefelter syndrome ; XXY, XXXY).

The so-called Barr test , in which hair, oral mucosa or blood are used for testing, was for a time part of the compulsory medical examinations of the participants in major sports competitions. At the 1968 Olympic Games, it replaced the previously customary optical examination after athletes had criticized it as degrading. This was introduced in the mid-1950s after it became known that the German athlete Heinrich Ratjen had taken part in the high jump at the Olympic Games in 1936 due to his living conditions as a woman with the name Dora Ratjen.

See also

Hermann Henking , discoverer of sex chromatin in fire bugs.

Individual evidence

  1. Barr ML, Bertram EG: A Morphological Distinction between Neurones of the Male and Female, and the Behavior of the Nucleolar Satellite during Accelerated Nucleoprotein Synthesis . In: Nature . 163, No. 4148, 1949, pp. 676-7. doi : 10.1038 / 163676a0 .
  2. ^ Lyon MF: Gene Action in the X -chromosome of the Mouse ( Mus musculus L.) . (abstract) In: Nature . 190, No. 4773, 1961, pp. 372-3. doi : 10.1038 / 190372a0 . PMID 13764598 .