A male-determining gene located on the Y chromosome determines the s*xual orientation of humans and other mammalian infants. But the Y chromosome in humans is deteriorating, and without a new s*x gene, we might all perish in a few million years.
The good news is that two mouse groups have successfully eliminated the Y chromosome. The spiny rat has evolved a novel male-determining gene, according to a new article published in Proceedings of the National Academy of Science.
How Y Chromosome is Disaappearing?
Mammals generally share our X and Y chromosomes; the X contains many genes while the Y has SRY and a few others. The imbalance between males and females in X gene dosage is a major flaw in this system. Can you explain the irrational evolution that led to this system? The surprising discovery is that the s*x chromosomes of Australia’s platypus are very dissimilar to those of mammals and are more similar to those of birds.
The platypus’ XY pair is a typical pair of chromosomes, with two identical components. The results of this study show that the X and Y chromosomes of mammals were formerly a typical set of genetic material. Therefore, over the course of the 166 million years that humans and platypus have been developing separately, the Y chromosome must have lost between 900 and 55 functional genes. About five genes would be lost per million years at that rate. In 11 million years, the last 55 genes will be lost forever.
While our prediction of the Y chromosome’s demise sparked a heated debate, assertions and counterclaims regarding the Y’s predicted lifespan continue to this day, with estimates ranging from infinity to a few thousand years.
Human S*x Determination and the Role of the Y Chromosome
Female humans, like female mammals in general, have two X chromosomes, whereas male humans have one X chromosome and one little Y chromosome. There is no correlation between the names and their shapes; the X represents an unknown. As many as 900 genes, most of which have nothing to do with s*x, are housed on the X chromosome. However, the Y chromosome only has roughly 55 genes and is otherwise dominated by basic repetitive DNA that appears to serve no functional purpose.
However, the Y chromosome is potent because it carries a crucial gene that initiates male development in the embryo. This master gene activates other genes that control testis development at around 12 weeks after conception. Since the embryonic testis produces male hormones (testosterone and its derivatives), the embryo will develop into a boy.
In 1990, researchers pinpointed SRY (s*x region on the Y) as the master s*x gene. It achieves its job by setting in motion a chain of genetic events that begins with the SOX9 gene, which is essential for male determination across all vertebrates despite not being located on s*x chromosomes.
Rodents With No Y Chromosome
The good news is that two mouse lineages have lost their Y chromosome yet are still alive and well today. The Y chromosome and SRY have vanished entirely in some species of mole voles in eastern Europe and spiny rats in Japan. Both s*xes still have X chromosomes, but some have two.
Hokkaido University biologist Asato Kuroiwa and his team have had more success studying the spiny rat, a group of three species native to various islands in Japan that are all critically endangered. The researchers led by Kuroiwa found that majority of the genes originally placed on the Y chromosome of spiny rats had been transferred to other chromosomes. However, she did not find any evidence of SRY or the substitution gene for it.
At long last, their proper identification has been published in PNAS. The group identified sequences present in male but absent from female rat genomes, refined these sequences, and checked each rat’s genome for them. The researchers found a very slight variation on rat chromosome 3 close to the important s*x gene SOX9. Every male and zero female carried a tinier duplication (just 17,000 base pairs out of more than 3 billion).
They postulate that this tiny amount of duplicated DNA comprises the switch that normally activates SOX9 in response to SRY. In mice, they observed that this duplication increased SOX9 activity, suggesting that it might make SOX9 functional without SRY.
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What Does This Mean For the Future of Men?
Humans’ evolutionary destiny has been called into question due to the impending loss of the Y chromosome. Parthenogenesis allows female-only lizards and snakes to reproduce using their own genetic material. In humans and other mammals, however, this is impossible since at least 30 essential “imprinted” genes can function only if they are inherited from the father.
Since sperm and men are required for reproduction, the elimination of the Y chromosome might spell the end of humankind. This new information lends credence to an alternate hypothesis, which holds that humans are capable of evolving a new s*x-defining gene. Phew! However, there are potential downsides to the emergence of a novel s*x-determining gene. And what if multiple new systems emerge independently in various parts of the world?
The split between mole voles and spiny rats is an example of how a “conflict” between s*x genes can result in the emergence of new species. As a result, a human visitor to Earth in 11 million years might find no humans at all or a number of distinct human species living in isolation due to their varied methods of determining gender.
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Human and other mammalian infants’ s*xual orientation is determined by a gene on the Y chromosome called DFNS4. However, the Y chromosome in humans is deteriorating, and we may all perish in a few million years unless we develop a new s*x gene.
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