In the whole process of mammalian evolution, the Y chromosome has been shrinking, but other genes that remain on the Y chromosome still play an important role in addition to determining sex.
Y chromosome is a dwarf relative to the other chromosomes we own. The 22 pairs of our 23 pairs of chromosomes are composed of two chromosomes of almost the same size, but the Y chromosome is simply a little dwarf relative to the X chromosome to which it is paired. 2-3 years ago Y chromosome has shared about 600 genes with X chromosome, and now the Y chromosome only 19 genes. A new study in the journal Nature today shows that the reduction of Y chromosomes has stopped.
Human chromosome
Scientists believe that Y chromosome has stabilized for 25 million years. The main reason is that the genes remaining on the Y chromosome are of vital importance to the survival of humans in addition to determining sex. Some genes can affect the synthesis of protein, and some can affect the expression of other genes, and some are responsible for splicing RNA fragments. They are in the heart, blood and other tissues of the body are playing a role. One of the authors of the article, Massachusetts Institute of Technology Whitehead Biomedical Research Institute of David Peggy that "the 'to the degradation of the Y chromosome' this label to a full stop.
In other scientists believe that the work of the Peggy team to Y chromosome re-name, there are still people that "degraded Y chromosome" theory is correct. Gennifer Grave, a geneticist at the Australian National University in Canberra, says the past few million years are just a period of calm in the long process of Y chromosome degradation. "At least two rodents have no need for Y chromosome," she said.
In 1950, the American Association of Human Genetics, the geneticist Kurt Stern published a speech, suggesting that Y chromosome basically no gene in the body was expressed. In 2002, Graves and other scientists published articles in Nature, noting that the Y chromosome was shrinking from early mammals to primates, and predicted that male chromosomes disappeared within 10 million years. This makes many people want to know whether men will disappear.
In order to test this theory, Peggy and his colleagues began to study the evolutionary history of Y chromosome. They compared the complete sequence of DNA on eight mammalian chromosomes. They began to study the species that appeared later, including rhesus monkeys, chimpanzees and humans, from the earlier species of fossil records - including opossums, cattle, rats, and mice.
Comparative studies have shown that Y chromosomes do exist for hundreds of millions of years, Peggy called "catastrophic genetic loss" changes. But this reduction has been halted 25 million years ago. "Y chromosome has been so stable for 25 million years, so that we can say that this change has stopped," Peggy said.
He suggests that this stability is derived from other 12 important genes on the Y chromosome that are independent of sex, sperm production, and male organ development. These genes on the Y chromosome are expressed in other tissues such as the heart and blood cells, Important cellular functions, such as protein synthesis and other gene transcription. In his opinion, this suggests that Y chromosomes play an important role in the survival of the whole body, so the sequestration of these genes is favored by evolution.
Andrew Clark, a geneticist at Cornell University, agrees that they will be particularly stable once these core genes have undergone a heavy test of the disappearance of unimportant genes on the Y chromosome.
But Grave is not so optimistic, she believes that stability is temporary. "The degradation of the Y chromosome is obviously not a linear process", "the final stage of degradation may be a big change." Japan has two kinds of rodents have completely lost the mammalian Y chromosome, many genes transferred to other chromosomes. She added that the two species of voles completely lost some of the Y chromosome genes, and their function may be replaced by other genes. "Although rodents have tested this strange new chromosome system before the primates, we should not be in the status quo," she concluded.
Peggy replied that he had observed the stability of these core Y genes in many species, so it was not possible to lose them further. "Maybe there will be, but I do not think that," he said.
The renewed Y and its widely distributed regulatory genes carry another topic for biologists. Peggy said: Men's cells and women's cells may be different in biochemical characteristics, with the Y chromosome associated with the gene man's cells and two X chromosomes will be slightly different, and these differences will not only Sex only. When biologists use cell lines to test, they usually do not care whether cells are derived from men or women. "For a long time we are studying cells are men and women," Peggy said, this may be incorrect. In the same trial, the XX cell line and the XY cell line may yield different results.
Why is this important? Peggy said that because some diseases such as autoimmune diseases, will affect women more, and other problems such as autism spectrum disorders are more affected by men. Biologists are trying to solve these puzzles from the cell level. In general, these minor biochemical differences have been ignored - because they do not compare male and female cell lines - which may affect their results. Now it is time to broaden our horizons.