What is the Y chromosome?

Y chromosome has always been a neglected part of the genome. The creator only designed this for humans.

The existing chromosomes seem to have little other function except to make developing embryos strong and aggressive.

However, Y chromosome has ushered in its spring, and the research on Y chromosome has become the frontier of genome research. Through research, scientists have made some very interesting discoveries.

David Page of Whitehead College in Cambridge, Massachusetts, USA is mainly responsible for the research of Y chromosome. He said: "In the past century, the Y chromosome has been ignored and misunderstood. Many people think that this is a desert with no research value. But I think, like Yellowstone National Park, it contains rich connotations. "

At present, researchers are trying to answer the following questions through the study of Y chromosome:

Where do we come from? How do humans develop their language ability? What is the difference between man and ape? Is the struggle between the sexes closely related to genes? (Perhaps, it is the Y chromosome that contains the secret of being a human being, enough to make feminists helpless. ) Adam or Eve comes first?

300 million years ago, there was no Y chromosome at all. At that time, most creatures had the same pair of X chromosomes, and their sex was determined by many other factors, such as temperature (once amphibians such as turtles and crocodiles failed to meet certain temperature requirements, all eggs would hatch into females). With the dramatic biological evolution, the Y chromosome appeared. This chromosome is mutated from a gene of mammalian X chromosome. David Page explained: "This mutation has produced an overbearing male sex-determining gene. It is no longer controlled by so many environmental factors, and the male world has emerged because of its existence. "

Usually, chromosomes in organisms are paired, each pair is identical, and the corresponding DNA fragments are frequently exchanged with each other. This exchange changes the genetic material and helps to eliminate harmful variation in species. Due to the genetic expansion of mutated DNA region, the exchange between X chromosome and its paired chromosome is less and less. With the passage of time, the Y chromosome was born. The plot of this chromosomal evolution story can be compared with any novel.

Y chromosome exists only in men. Any egg carrying Y chromosome and sperm meet and fertilize, which produces a male; A woman is born when an egg meets a sperm with X chromosome and is fertilized. This is why the Y chromosome is the source of male life information, and it can also be said to be a genetic version of the Bible genealogy. Humans are born from the same root.

By measuring the variation of Y chromosome, researchers can show whether men of different races have a common ancestor. For example, the Lamba people living in southern Africa belong to the black race, but they have been passed down from generation to generation as Jews. They were originally metalworkers living in Yemen, and later moved to southern Africa because of the disaster. Some people get married and have children in the local area and settle down. After testing by researchers, it is found that the variation pattern of Y chromosome of Ramba people is very similar to that of Gaosha people of Jewish race. Another study also found that Israelis and Palestinians had the same ancestor 7800 years ago.

There has been a qualitative leap in the field of genetic archaeology. On the whole, these amazing discoveries constitute a magnificent picture. Nature Genetics, a famous scientific journal, published the latest human pedigree map, which absorbed the research results of Y chromosome variation. Studies have confirmed that the birthplace of mankind is in Africa. Through the study of Y chromosome, it is also found that the X chromosome appeared 84,000 years earlier than the Y chromosome peculiar to men.

At the end of the ice age, Indians came to the virgin land of North America as mammoth hunters. Indians are unanimously regarded as the earliest human beings in this land. But more and more evidence shows that there were people in this land before the arrival of human beings. In the past few years, some ancient human skull fossils have been unearthed in North America. According to calculations, they arrived in America earlier than the Indians, and their appearance and facial features were far from those of North Asians. On the contrary, they look more like people from Southeast Asia and the Pacific. Douglas Wallace of the Molecular Medicine Research Center of Emory University School of Medicine in Atlanta, USA, discovered a group of mutant genes named "haplogroup X" by studying mitochondrial DNA. This variant gene is found in Indians and Europeans, but not in Siberia and Southeast Asia. In addition, earlier this year, Dr. Spencer Wells of the Center for Human Genetics of Oxford University published a paper and published the latest research results on this issue. By studying the Y chromosome, he thinks that the ancestors of Europeans and Indians were Central and South Asians 40,000 years ago.

Y chromosome can not only tell us the migration route of the ancients, but also tell you how many genetic codes you have in common with people with the same surname. Professor Brian Sykes from the Institute of Molecular Medicine at Oxford University said: "We found an amazing connection between a person's genetic organization and his surname." This connection comes from the fact that a person inherits his surname and Y chromosome from his father. After studying the genes of people with the same surname, Professor Sikes found that 50% of them have the same Y chromosome. This means that the Essex clan has maintained their blood relationship since this surname appeared in England 700 years ago. Further research shows that the proportion of other surnames with the same Y chromosome is the same. The study also found that unfaithful marriages are not as much as 5% to 10% estimated by other methods. By studying the genes of people named Sykes, this situation only accounts for less than 1%. The research results can also be applied to the detection of criminal cases: by analyzing the DNA left by criminals at the scene, the names of criminals can be quickly known. Weapons on the sexual battlefield

The study of Y chromosome also found that sexual struggle is rooted in genes. Male sperm contains toxic components, which can destroy one male sperm and another male sperm when they meet, thus ensuring their competitive advantage. The evolution of human beings proves that the competition between semen is the result of natural selection. Among primates, chimpanzees are the best example. Male chimpanzees can produce a lot of sperm. Because female orangutans usually have sex with many male orangutans, the more sperm they produce, the greater the chance of meeting eggs.

Last year, Dr. Wu Zhongyi of the University of Chicago and his colleagues found that the gene mutation related to protein production in semen of both human beings and orangutans was very rapid. Dr. Wu said: This shows that their competitive pressure is very great. "the y chromosome contains a large number of genes that produce semen. Researchers are looking for which genes are involved in this competition. "

Y chromosome may put a baby boy in danger of not being protected by his mother's immune system in the womb. Professor Rey Blanchard of the University of Toronto also made an amazing discovery: among brothers (excluding sisters), the younger ones have slight behavioral disorders than the older ones. The more older brothers there are, the more serious the behavior disorder of younger brothers will be. Previous studies have found that between brothers, the more brothers, the easier it is for younger brothers to become gay. What is the reason? Blanchard thinks that the problem may be the Y chromosome. There is a gene in Y chromosome that can produce a male protein called AMH, which can prevent the development and formation of male uterus and ovary. But AMH can also trigger the mother's immune system, and the antibodies produced will affect the development of fetal brain.

Although most genes are honest and will only stay safely in their own chromosomes, jumping genes are like tramps in the genome. After staying in one place for many years, they will suddenly leave the previous chromosome and irregularly enter another chromosome. They can break into a gene, destroy it, or stay next to a gene and gradually change its function. David Page discovered that DAZ was the first "immigrant" on the Y chromosome.

Before that, it was generally believed that there was a gene named SRY on the Y chromosome, which was the key to let the uterus have boys. Now we know that the Y chromosome contains at least 24 genes, while the X chromosome has 2000 or more genes, which is unique among chromosomes. Most genes in the Y chromosome are responsible for making sperm or helping cells complete their work, such as making protein.

DAZ gene may have reached the Y chromosome about 20 to 40 million years ago. It is considered as a producer of sperm. Without sperm, men can't produce sperm. About one in six couples suffer from infertility, and 20% of them are caused by male sperm problems.

Contemporary in vitro fertilization technology provides a solution: a selected sperm is injected directly into the egg and fertilized in vitro. But it also brings serious problems. Infertility may be passed on to future generations-infertility becomes a genetic disease for the first time. David Page said: "Artificial assisted fertilization will bring infertility to this family, and all men in this family can't have offspring without outside help." Creative ape differentiation

Besides making sperm, the latest and boldest idea of Y chromosome comes from British researchers. They put forward a controversial view that the jumping gene on Y chromosome is the key to the development of human language ability.

DAZ gene can produce sperm, which enables our primate ancestors to thrive in the family, but there must be something in our genes that marks the parting of ways between humans and apes. This is a research project of Tim Crowe from the Department of Psychiatry, Oxford University. He believes that in the process of human evolution, there is a gene that appeared relatively late, and it is this gene that changed the development mode of the brain, thus giving us language ability. Not only that, he also thinks that this gene will be slightly different between men and women. Another research team also announced that they had found a gene with the same function on the Y chromosome.

"We found this gene in the human brain, but not in the ape brain," said Dr. Affara of Cambridge University. "It is probably the gene that enables human beings to master the language ability." There is a similar gene (PCDHX) on the X chromosome of apes, but in the process of human evolution, this gene jumped to the Y chromosome (PCDHY).

The time when this gene was transferred to the Y chromosome arm was about 3 million years ago, when the volume of human brain began to increase and tools began to appear. However, outside the control of Y chromosome, the DNA carrying PCDHY can divide or change its position by itself, so it is difficult to determine the exact time at present.

What did the gene do? At present, there are far more questions than answers. Behind all these new discoveries about the Y chromosome, there is one of the biggest mysteries. Because the Y chromosome is like a typical capitalist economy, the winner is king and the loser is kou. The genes that can survive must have values that we don't know yet. Affara said: "Y chromosome lost many genes in the process of evolution. The question is, why do some always exist? They must have some unknown function. " Genetic archaeologists are studying this, hoping to find the answer.