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New discoveries about the repair mechanism of the Y chromosome

This is how the Y chromosome ensures that the male species will survive* A unique mechanism allows the male chromosome to repair itself

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In the top photo, Dr. David Page, head of the team of researchers, yesterday in Washington. The chromosome has adapted unique features to itself and contains a "backup" copy of itself
In the top photo, Dr. David Page, head of the team of researchers, yesterday in Washington. The chromosome has adapted unique features to itself and contains a "backup" copy of itself

The male species will disappear within five million years, scientists believed until recently: the Y chromosome, found only in the male chromosome system (therefore called the "sex chromosome"), cannot repair the defects created in it over the years. But the estimates of the extinction of the male sex were premature, according to a study published yesterday in the USA. In the research, it was discovered that the Y chromosome has an unusual mechanism that allows it to repair itself without the help of other chromosomes, and it carries a more important genetic load than assumed.

Humans have two sets of 23 chromosomes, which carry their genetic load. When a sperm meets an egg, it carries one set of 23 chromosomes from the father and fertilizes the egg carrying a second set of 23 chromosomes from the mother. The sex of the fetus is determined at the moment of fertilization; Half of the sperm contain an X chromosome and the rest contain a Y chromosome. The egg contains a chromosome. X If a sperm with an X chromosome penetrates the egg, it will develop into a daughter (XX); When a sperm with a Y chromosome penetrates the egg, it will develop white (XY).

The fact that only men carry the Y chromosome creates a problem. "All chromosomes come in pairs, one from the mother and the other from the father," explains Prof. Yoram Groner, a researcher in the Department of Molecular Genetics at the Weizmann Institute. According to him, "while dividing the cell, they perform a 'mating dance' in which they exchange parts of different chromosomes - genetic material. This 'dance' serves as a repair laboratory; Damages caused to the genetic load over the years are repaired before they are passed on to the offspring. The Y chromosome cannot participate in the 'dance' because it does not have an identical partner. And with the exception of tiny parts, it cannot replace parts and repair itself against the X chromosome. For this reason, the scientists believed that it is in a continuous process of deterioration as a result of errors and malfunctions occurring in it."

The study, which is published in the magazine "Nature" shows that in the process of evolution the Y chromosome has adapted to itself features that distinguish it from the other chromosomes, and it contains a "backup" copy of itself - a sort of mirror image. The researchers, from the Whitehead Institute at the University of Cambridge in the USA, discovered that the Y chromosome consists of eight palindromic segments (segments that can be read the same in both directions, similar to the word 'father') of the letters H-N-A. The genetic sequences consist of four letters that represent chemical bases: A, T, C and G. However, there are only two possibilities of pairing the letters: A connects only with T and C connects only with G.

To maintain the integrity of the genetic load, the palindromic regions fold in half - so that each letter stands opposite the letter to which it can connect. In the event that there is a change in the genetic sequence due to a mutation, one arm of the folded genetic sequence works to replace the damaged letters found in its left arm. Between the palindrome areas there are "normal" areas where gardens are also located.

In the past, scientists estimated that the X and Y chromosomes carry about a thousand genes each. Today, it is known that the Y chromosome contains less than a hundred genes. For this reason, Prof. Gruner said, the scientists believed that the Y was a negligible chromosome that did not carry important genes. "If he carried important genes, new genetic diseases would appear every few generations due to his inability to repair himself," he said. "The fact that diseases do not appear with such a high frequency made the researchers think that the really important genes are on other chromosomes that manage to repair themselves, and that within a few million years, even the few genes that remain on the Y chromosome will disappear."

According to Dr. David Page, who headed the team of researchers, after the lengthy process of mapping the Y chromosome, it was discovered that the chromosome contains 78 genes - some of which are responsible for the fertilization mechanism of the sperm and the egg, and some of which are related to other biological processes. "This study may open the door to research in the field of fertility," says Prof. Keren Avraham from the Faculty of Medicine at Tel Aviv University. "The genes on the Y chromosome are probably related to activities related to reproduction, and defects in the genes may explain fertility problems."

Among other things, the authors of the study believe that it is possible that the genes on the Y chromosome explain the difference between women and men regarding susceptibility to diseases. Women suffer more from osteoporosis (bone thinning due to calcium loss) than men. It is possible that the men's immunity to the phenomenon stems from the genes found in the chromosome. "This is an extraordinary study," says Prof. Avraham. "He orders more studies to follow him, and throws in the trash all the jokes they told about chromosomes." Y

Dr. Page also pointed out that the results of the study require further testing of the genetic load carried on the Y chromosome. "Can we, following the analysis of the Y chromosome, answer the eternal question why men - unlike women - find it difficult to pull over the car and ask how to reach their destination? Not yet," he said.

The genetic difference between men and women - like between a human and a chimpanzee

At a press conference called due to the discovery, Dr. David Page, who headed the team of researchers, said that the results of the study have interesting implications. For example, until now scientists believed that there was a minimal genetic difference between men and women. This is because both men and women have one X chromosome, and even though women have an additional X chromosome, it is inactive.

Recent studies have revealed that several hundred genes located on the inactive X chromosome are active nonetheless. Considering that there are nearly 80 genes unique to men on the Y chromosome, it appears that the genetic difference between men and women is much greater than previously thought and is estimated at 2-1% of the genetic load - like the difference between a man and a male chimpanzee or between a woman and a female chimpanzee.

"We all quote the saying that my sons are more than 99% identical when it comes to their genetic makeup," Page said. "But the reality is that the genetic differences between women and men are so great that they dwarf all the other differences that exist in the human genome."

Source: Yuval Dror, Haaretz

A video about the discovery on the BBC website

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