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The women's chromosomes have the X factor

X chromosome may protect women's health

Avi Blizovsky

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Women are much more genetically diverse than men, according to a recently published analysis of the X chromosome. A large group of scientists published a detailed profile of the DNA sequence in the journal Nature.
They found that in female mammals, which are known to contain two copies of the X chromosome, more genes are expressed than in males, which have one X chromosome and one Y chromosome.
They also said that women are more protected from many diseases due to this duplication of the X chromosome. "The X chromosome is the most unusual in the entire human genome in terms of its biology and its relationship to disease," said Mark Ross, project manager at the Wellcome Trust Sanger Institute in the UK.

The X chromosome, one of the 24 different chromosomes found in human cells, is much larger than its Y counterpart, and contains 1,098 genes compared to the 78 genes contained in the Y chromosome. This means that the female mammalian body contains many more genes than the male. To compensate for these thousand chromosomes, the woman's body turns off the activity of one of the X chromosomes in each cell quite randomly, thereby equalizing the production of proteins between the sexes.
Tortoiseshell cats have a mixed expression of both X chromosomes. This is a random expression of the chromosomes that causes the recognizable color of the cat's skin.
Females of this species have genes for one color on one of their X chromosomes and a gene for another color on the other chromosome, resulting in a mixture on the animal's fur leading to a multicolored pattern.
However, the researchers recently discovered that the "silent" X chromosome in females is not completely silent. Some of his genes managed to escape the silencing. This means that females actually express more genes than males.
"It seems that 15% of genes escape induction, and each of them becomes a candidate to explain the differences between men and women" says Robin Lovell-Badge from the National Institute for Medical Research in the UK.
Moreover, an additional ten percent of the genes are sometimes active and sometimes inactive, and this provides a mechanism that gives women greater genetic variation than men. "I always thought they were more interesting." said

The X chromosome can also protect or harm health, depending on your sex. Although no one knows why the Y chromosome has shrunk so much, its shrinkage is not so harmful thanks to the X chromosome. In this sense, it doesn't matter so much if a man lacks a gene on his Y chromosome because he has a copy on his X chromosome. However, this makes men vulnerable to any problem that appears on the X chromosome. Diseases on the X chromosome are manifested externally in males because they do not have the copy of this gene on their second chromosome. says Dr. Ross. "Over 300 conditions have so far been linked to the X chromosome. Among them are serious diseases including hemophilia, autism, muscle weakness and mental retardation. However, because women have a different copy of the X chromosome, usually a healthy copy, they are protected from the effects of these disorders. Men, on the other hand, who have no backup, are forced to fully express these defective genes.
Because men only have a single X chromosome, more diseases associated with this chromosome occur in them than in women, says Dr. Ian Jackson of the Division of Human Genetics at the MRC, UK. "One of the consequences is that boys have a greater risk of mental retardation than girls."
The high quality of the DNA sequences published in the article has already helped to identify a large number of disease genes. There are many more that will surely be discovered thanks to this valuable genome." said.
Prof. Mike Starton, also from the Wellcome Trust, said that a deeper understanding of these harmful genes on the X chromosome may allow scientists to intervene to prevent the onset of mental retardation.
"Even though it sounds like fantasy, this is the implication of this study," said Emretz, "so we must not forget that the understanding of these genes may allow us to prevent their appearance.
Men also have another reason to feel sorry for their genetic baggage. New Scientist magazine reported that although men may suffer from mental retardation, they are also the most likely to be geniuses. Although the average IQ of men and women is the same, men are more frequently at both extremes of intelligence. This is due to the fact that if you have genes for high intelligence on the X chromosome you mix them with average genes on the other chromosome.

For news at the BBC
The human genome scientist

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