Most mammals have X and Y chromosomes similar to ours; An X with lots of genes, and a Y with SRY and a few others. This system comes with problems due to the unequal amount of X genes in males and females.
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The sex of humans and other mammals is determined by a male-determining gene on the Y chromosome. But the human Y chromosome is dwindling and could disappear in a few million years, if we discovered a new sex genes did not develop, we extinct Can be. The good news is that two lineages of rodents have already lost their Y chromosome and are still alive. National Academy of Science A new paper in Proceedings shows how the spiny rat has evolved a new male-determining gene.
How does the Y chromosome determine sex in humans
In humans, as in other mammals, females have two X chromosomes and males have one X and a smaller chromosome called a Y. The names have nothing to do with their size. There are about 900 genes in the X that do all kinds of work related to sex. But Y has few genes (about 55) and lots of noncoding DNA—simple repetitive DNA that doesn’t do anything.
But the Y chromosome does something special because it contains an important gene that initiates male development in the embryo. About 12 weeks after conception, this master gene passes on other genes that control the development of the testis. The fetal testes make male hormones (testosterone and its associated hormones), which ensure that the child develops into a boy. This master sex gene was identified as SRY in 1990. It works by triggering a genetic pathway starting with a gene called SOX9, which is important for male sex determination in all vertebrates, although it is not based on sex chromosomes.
missing y
Most mammals have X and Y chromosomes similar to ours; An X with lots of genes, and a Y with SRY and a few others. This system comes with problems due to the unequal amount of X genes in males and females. How did such a strange system develop? The surprising discovery is that platypuses from Australia have completely different sex chromosomes, similar to those of birds. In the platypus, the XY pair is just a simple chromosome, consisting of two identical members. This suggests that mammals had a common pair of X and Y chromosomes not too long ago.
This must mean that the Y chromosome has lost 900-55 active genes in the 166 million years that humans and platypuses evolved separately. This is a loss of about five genes per million years. If this loss continues at the same rate, then the last 55 genes will also go away in one crore 10 lakh years. The good news, though, is that we know of two rodent lineages that have already lost their Y chromosome – and are still alive.
The mole voles of Eastern Europe and the spiny rats of Japan each have some species in which the Y chromosome and SRY have disappeared completely. Although it is not yet clear how mole voles determine sex without the SRY gene, a team led by Hokkaido University biologist Asato Kuroiwa got a chance to get to know the spiny rat better—three species found on different Japanese islands. A bunch of, all endangered.
Kuroiwa’s team found that most of the genes on the Y of spiny mice were transferred to other chromosomes. But it did not find any indication of SRY, nor did it find alleles for it. Now finally he has published a successful identification in PNAS. The team found sequences that were in the genome of the male, but not the female, then refined and tested the sequence on each mouse.
What they discovered was a small difference on chromosome three of the spiny rat near the key sex gene SOX9. A small duplication (only 17,000 base pairs out of more than three billion) was present in all males and none in females. They suggest that this small segment of duplicated DNA contains the switch that normally turns on SOX9 in response to SRY. When they introduced this duplication into mice, they found that it increased SOX9 activity, so the change may allow SOX9 to function without SRY.
what this means for the future of men
Some lizards and snakes are female-only species and can produce eggs through a process known as parthenogenesis. But this cannot happen in humans or other mammals because we have at least 30 important genes that work only when they come from the male via sperm. To reproduce, we need sperm and we need men, which means that the end of the Y chromosome could be a harbinger of the extinction of the human race. The new finding supports an alternative possibility that humans may have evolved a new sex-determining gene.
However, the development of a new sex determining gene comes with risks. What if more than one new system develops in different parts of the world? A ‘war’ of sex genes can lead to the separation of new species, which is exactly what happened with mole voles and spiny rats. Therefore, it is possible that after 11 million years there may be no humans on Earth – or that there may be several different human species, kept separate by their different sex determination systems.
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