It was observed that the Y chromosome, which can be found in males, vanished among a particular rat species, as noted by Newsweek. These findings prompted scientists to dig deeper into the possibility of this happening in a human context.
However, an article published in PNAS notes that this isn't bad news for men. The scientists of the study note that despite the disappearance of the Y chromosome, it doesn't equate to the extinction of males.
The X and Y Chromosome
In biologically born women, the sex chromosome pair consists of two copies of the same kind of chromosome. This gives them the XX genotype. Males, on the other hand, have a Y chromosome in their pair, granting them the XY genotype.
According to Newsweek, Jenny Graves, a geneticist that focuses on sex chromosomes, notes that this chromosome hardly holds genes while it keeps a lot of DNA clutter. However, Graves mentions that the kept genes also contain SRY, which is the gene that determines a male.
The other genes kept on accumulating and worked towards preserving this male-determining package. To do so, these genes stopped exchanging with X. As a result, the gene was stuck and could not perform any self-repair. Hence, it ended up rapidly deteriorating and, later on, reaching its current state.
Newsweek notes that this observation was seen in Y chromosomes across various species in the animal kingdom. For one, the spiny rat, one among many mammals, was entirely rid of the Y chromosome.
Grave notes that the Y chromosome in humans is in the latter phases of deterioration. Hence, the issues at hand are how long it will stay until it eventually disappears and what the effects of its absence will be.
Male Spiny Rats Without the Y Chromosome
While the loss of the Y Chromosome may imply extinction of the specific population, it was observed that male spiny rats still existed. According to New Scientist, a team of researchers studied this by organizing male and female genomes in a sequence. However, in doing so, the team did not find any variants that were only unique to the male rat.
The researchers then dug deeper and observed that in these male rates, one out of the two chromosome 3 copies had a region that was duplicated. This was right beside the SOX9.
The team conducted various experiments to test whether duplication enforced SOX9 activity and effectively took the place of SRY. This may imply that a chromosome 3 with a duplicate will become proto-Y, while the chromosome 3 without the duplicate will be proto-X.
According to New Scientist, Robin Lovell-Badge-a researcher who contributed to the discovery of the SRY-noted that the team would have to remove the duplication found in spiny rats to prove that there were no males that developed. However, doing so was not possible because the spiny rat was an endangered species.
Nevertheless, Graves notes that the work is brilliant and compelling. She mentions that there is no reason to think that a human male's Y chromosome is more robust than that of a spiny rat.
Despite this, Lovell-Badge notes that the Y chromosome is performing well and is not at current risk of disappearing in humans and other types of mammals. He further states that the disappearance of this chromosome in the evolution of mammals is rare.
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