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The Y chromosome is slowly disappearing

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The sex of newborn boys is decided by a male sex-determining gene on the Y chromosome, females have two X chromosomes. The X contains about 900 genes that perform all sorts of non-sex-related activities. The Y chromosome contains a key gene that initiates male development in the embryo. At about 12 weeks after conception, this main gene activates others that regulate testicular development. The embryonic testicle produces male hormones (testosterone and its derivatives), which ensure that the child develops as a male. We have a problem, though: the human Y chromosome is degenerating and disappearing. An article published in Nature this year suggests that the degradation of the chromosome is stable and this suggests that there are two possibilities: the loss of genes from the Y could stabilize producing other essential genes anyway or there could be a faster loss and the Y could disappear in a few million years, leading to our extinction. Unless we evolve to produce a new sex gene .

 

The good news is that two rodent species have already lost their Y chromosome but still survived. A new article published in the Proceedings of the National Academy of Science shows that the Indomalayan spiny rat ( Maxomys surifer Miller, 1900) has a new gene in its genetic makeup that determines male sex.

The study, developed by Hokkaido University biologist Asato Kuroiwa and his team, found that in these rats, males and females have only one X chromosome (XO/XO) and the Y chromosome is completely lost. Most of the genes in the Y of spiny rats were transferred to other chromosomes, thus uncovering sequences that were found in the genomes of males but not females.

The new finding therefore supports an alternative possibility: humans could develop a new gene that determines sex. However, the evolution of a new gene that determines sex could lead to some strange evolutions. What if more than one new gene system evolved in different parts of the world? A “war” of sex genes could lead to the separation of new species, something that has already happened in some animals, such as platypuses, mammals that have sex chromosomes more similar to those of birds and completely different from other mammalia .

 

So if someone visited Earth 11 million years from now, they might not find any humans — or different human species, kept apart by their different sex determination systems.

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  • Turnover of mammal sex chromosomes in the Sry-deficient Amami spiny rat is due to male-specific upregulation of Sox9. (pnas.org)
 

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