Corpuscle of Barr

See also: Barr

The corpuscle of Barr is component core of the Femelle S of Mammifère S. It was discovered in 1948 by Doctor Murray Barr with the Canada.

It is also called body chromatinien of Barr or sexual chromatin . It is sexual Hétérochromatine applied against the inner face of the nuclear Enveloppe of the majority of the somatic cell S at the Femelle S of Mammifère S. It corresponds to the one of both X chromosomes inactivated, indifferently of maternal or paternal origin. This inactivation is held in the early stages of embryogenesis, and inactivated X chromosome is maintained during the cellular division: a cell inactivant X chromosome dividing governor then will give 2 cells in which X chromosome governor will be inactivated. Thus, all the descent of a cell will carry same X chromosome inactivated. One speaks then about mosaicism.

Utility

At the Mammifère S or the Drosophile, the Y chromosome comprises that very little information. The X chromosome as for him comprises some much more (1100 Gène S on the X chromosome of the Souris). But the majority of these Gène S are not implied in the sexual characteristics. They are genes of metabolism, of household,…

In the female, there are thus two Allèle S for genes carried by X, whereas there is only one in the male of them, from where a problem of proportioning genic. With the wire of the evolution, the Life found two solutions for stage with this problem:

- the form of genes of X chromosome of the male is twice stronger, to compensate for two X chromosomes females (it is the case of the Drosophile for example);

- the expression of one of two X chromosomes of the female is repressed, to compensate for only X chromosome male (it is the case of the Mammifère S);

In the mammals, the process which consists during the Embryogenèse has to repress the expression of one of two X chromosomes, by putting it in the form of Hétérochromatine optional (forming the corpuscle of Barr) is called Lyonisation, of the name of Marie Lyon, having discovered this process in 1963.

Corpuscle of Barr and sport

Generally, the presence of a corpuscle of Barr in the cells signs the sex female, which resulted in using this test like Test of femininity for the sporting tests.

In spite of the fact that this test made it possible to eliminate from truths cheaters (men contributing in the female category), it also made eliminate from true patients, women with the abnormal chromosomic chart (XY instead of XX, or disease of the Testicule feminizing). This is why it was abandoned.

Cat-like anecdote

The color of the peeling of the Chat is related to X chromosome. Owing to the fact that the males have only one X, they can carry only one color (black or russet-red), in addition to the white (absence of color).

On the other hand, the she-cats can have two different colors, one on each X, of which one or the other is inactivated in the form of corpuscle of Barr, according to the zone of the body.

This is why the tricolor cats are always she-cats.

Human anecdote

Human X chromosome carries a gene implied in the development of the glands sudoripares. Transmission of X carrying a change of this gene led to many anomalies of the development. However, among women hétérozygotes (carrying the change only on one of two X chromosomes), the inactivation of one or the other of X chromosomes in a random way leads to reduced symptoms. One of the symptoms is the absence of sudation. These women have zones of the skin thus where sudation is normal, others where sudation is not done, leading to a local rise in the cutaneous temperature. One speaks then about " points chauds" of the woman.

Another symptom of this anomaly is a more or less marked attack of the skin (the collagen fibers can be rare or fragmented), Phanère S (the pilous follicules are reduced) and of the teeth (absence of the dental germs).

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