What might the future look like in a world without men? Recent studies indicate that the Y chromosome, a crucial factor in determining male identity, is experiencing malfunctioning.
The Y chromosome has already undergone significant degeneration and could potentially vanish entirely. But what implications would this disappearance have?
Could new sexes emerge? Or could the male species face extinction? Renowned Australian geneticist Jenny Graves, an expert on the Y chromosome, sheds light on these developments.
Why is the Y chromosome disappearing?
First, let’s revisit the concept of sex chromosomes. Women typically have two X chromosomes, while men possess one X and one Y chromosome.
These chromosome pairs, which account for about 4% of an individual’s DNA, play a vital role in determining sex.
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“Chromosomes typically occur in pairs, with men and women sharing the same sex pairs. Women have two large X chromosomes, whereas men have one X and one Y,” explains Graves.
“In comparison to the X chromosome, the Y chromosome is relatively small, containing only 45 genes, with one gene determining maleness and several others involved in sperm production. The remaining genes serve uncertain purposes. By contrast, the X chromosome contains 900-1400 genes.
Originally, the Y chromosome had over 900 genes similar to the X chromosome. Presently, only 45 genes remain. These sex chromosomes evolved from identical non-gender-associated chromosomes, rendering much of their current makeup functionally redundant.
The degeneration of the Y chromosome is not unique to humans; it also occurs in other species. For instance, fruit flies have lost the majority of their Y chromosomes.
“The loss of the Y chromosome seems to stem from a couple of factors. The Y chromosome is exclusively present in the testes, never in the ovaries; thus, it is constantly exposed to mutations during sperm production,” explains Graves.
“Sperm production involves numerous cell divisions, each susceptible to mutations that can substantially affect the chromosomes. Moreover, the Y chromosome cannot engage in genetic exchange, hindering its ability to repair mutations effectively.”
Most chromosomes repair mutations by exchanging DNA with their counterpart chromosome, a process known as recombination. However, the Y chromosome, inherited singly unlike the dual X chromosomes in women, lacks this mechanism for genetic exchange.
What does this mean for the future of the male species?
Compared to its original state, the human Y chromosome has lost 97% of ancestral genes, while the X chromosome remains relatively intact.
What are the implications of this rapid degeneration for the male species? Are we on the verge of a world devoid of human males?
“When I mention rapid degeneration, I refer to an evolutionary timeframe. Sex chromosomes have undergone roughly 180 million years of evolution in mammals. It took this long for the Y chromosome to erode to its current state,” notes Graves.
“The impending loss of the Y chromosome has stirred concern in some quarters. A rough estimate suggests it might take another six or seven million years before the chromosome completely disappears.”
Unless global billionaires achieve immortality breakthroughs, humans may never witness the initial stages of Y chromosome degradation. But hypothetically, what might this development entail?
While some species can reproduce through parthenogenesis (unfertilized egg development), humans require sperm-bearing genes for optimal functioning. These genomically imprinted genes necessitate male involvement for reproduction. However, viable alternatives exist.
“Evolving new sex-determining genes could pave the way, as seen in certain rodent species like the eastern European mole rat and Japanese spiny rat, which lack a Y chromosome entirely. These rodents adapted by relocating crucial Y chromosome genes to other chromosomes.”
Although successful in rodents, this strategy may not yield the same results in humans. While creating new sex genes is feasible, the ensuing clash between old and new genes poses uncertainties.
“This gene conflict scenario could potentially lead to divergent sex-determining systems across human populations,” Graves explains. At present, these speculations predominate. While the Y chromosome’s deterioration is evident, the future outcomes remain uncertain, encompassing the possibility of evolutionary changes resulting in new sexes.
Given the Y chromosome’s peculiarities and the substantial human population, Graves suggests that an individual born without a Y chromosome might already exist somewhere in the world, broaching intriguing evolutionary prospects.
About our expert Jenny Graves
Jenny Graves is a geneticist and professor at the La Trobe Institute for Molecular Sciences. She has authored over 430 articles and four books on genetics, establishing herself as a leading authority on human evolution and the evolving landscape of the Y chromosome.
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Source: www.sciencefocus.com
