End of the Y chromosome?

[Tessa K]

Would someone who knows more about this than me explain if it's good science?

https://www.sciencefocus.com/the-human- ... chromosome

[Woodchopper]

From the article

“When I say rapidly, I’m talking in the evolutionary sense. Sex chromosomes evolved in mammals roughly 180 million years ago. It has taken that long for the Y chromosome to erode to this level,” says Graves.

“It’s funny that people get so upset about the loss of the Y chromosome. My rough calculations are that we’ve got another six or seven million years until the chromosome is completely gone.”

IMHO any prediction based upon what'll happen in six million years time is pretty speculative. During such a long time it seems equally plausible that humans will either become extinct, or we'll be so advanced that we'll have stopped caring about chromosomes millions of years before.

[Tessa K]

From the article

“When I say rapidly, I’m talking in the evolutionary sense. Sex chromosomes evolved in mammals roughly 180 million years ago. It has taken that long for the Y chromosome to erode to this level,” says Graves.

“It’s funny that people get so upset about the loss of the Y chromosome. My rough calculations are that we’ve got another six or seven million years until the chromosome is completely gone.”

IMHO any prediction based upon what'll happen in six million years time is pretty speculative. During such a long time it seems equally plausible that humans will either become extinct, or we'll be so advanced that we'll have stopped caring about chromosomes millions of years before.

That was my thought based on instinct

[Stranger Mouse]

From the article

“When I say rapidly, I’m talking in the evolutionary sense. Sex chromosomes evolved in mammals roughly 180 million years ago. It has taken that long for the Y chromosome to erode to this level,” says Graves.

“It’s funny that people get so upset about the loss of the Y chromosome. My rough calculations are that we’ve got another six or seven million years until the chromosome is completely gone.”

IMHO any prediction based upon what'll happen in six million years time is pretty speculative. During such a long time it seems equally plausible that humans will either become extinct, or we'll be so advanced that we'll have stopped caring about chromosomes millions of years before.

That was my thought based on instinct

Isn’t this like the “all women will be beautiful and all men will have big penises” thing the CHF took the piss out of?

[Lew Dolby]

I hate this simplistic view of genetics. "All women are xx, all men are xy" stuff

Apart from the fact most people don't know what chromosomes they have, there are people walking around who are 47 XXX, 47 XXY, 47 XYY - Kleinfelter syndrome and the rest.

[Grumble]

Surely the way to think about the Y chromosome is that it’s stuck around with only a few genes because those needed to be conserved, rather than the chromosome has degenerated? There’s no particular advantage to a chromosome being big, surely?

[Allo V Psycho]

No, the article is confused/ing.
The Y chromsome carries the SRY gene, which initiates male sexual development. This can already translocate to another chromosome, and you can get a 46 XX male
https://www.sciencedirect.com/science/a ... 2915323314
This individual is pretty much a normal male, but because there are a few other genes on the Y which support sperm development and were therefore absent, he sought help for infertility, which is how he was identified. This is a rare condition (but there may be other individuals like this, undetected). If the other genes on the Y also translocated (or the Y chromosome pretty much as a whole became part of another chromosome), then the 'Y chromosome' might disappear but we would still have male and female sexual development controlled by SRY but in a different place.
The article indicates that this has already happened in a vole and a rat, so no, it doesn't have to take millions of years. It COULD happen overnight.

Looking at all the direct quotes from Jenny Graves, they all seem fine. It's the journalist parts of it that are misleading. These say

Right now, this is all speculative. The Y chromosome is degrading, that much is clear. The future result, on the other hand, is less so. In millions of years, men could simply cease to exist. We could equally see an evolutionary change with an entirely new sex forming.

'Men wouldn't 'simply cease to exist - they would arise through a different deployment of genes on chromosome. And 'an entirely new sex'' is nonsensical.

In fact, with so many humans around the world and the innate weirdness of the Y chromosome, Graves believes that somewhere there could already be a man born without a Y chromosome for the first time.

As for "Graves believes there could already be a man born without a Y chromosome" that's not a direct quote and I'm pretty sure Graves knows that there are such individuals. It's the journalist who is confused.

[Allo V Psycho]

I hate this simplistic view of genetics. "All women are xx, all men are xy" stuff

Apart from the fact most people don't know what chromosomes they have, there are people walking around who are 47 XXX, 47 XXY, 47 XYY - Kleinfelter syndrome and the rest.

It's way stranger than just those conditions, Lew. At the gene/chromosome levels there are chimaeras with both male and female cells, including true hermaphrodites, and XX males as I've just posted. At the hormone level, there is complete androgen insensitivity: XY individuals who appear as normal females. And then the behavioral level - people who are entirely conventional in their genes, hormones and anatomy, but self-identify as a different gender.

[jimbob]

No, the article is confused/ing.
The Y chromsome carries the SRY gene, which initiates male sexual development. This can already translocate to another chromosome, and you can get a 46 XX male
https://www.sciencedirect.com/science/a ... 2915323314
This individual is pretty much a normal male, but because there are a few other genes on the Y which support sperm development and were therefore absent, he sought help for infertility, which is how he was identified. This is a rare condition (but there may be other individuals like this, undetected). If the other genes on the Y also translocated (or the Y chromosome pretty much as a whole became part of another chromosome), then the 'Y chromosome' might disappear but we would still have male and female sexual development controlled by SRY but in a different place.
The article indicates that this has already happened in a vole and a rat, so no, it doesn't have to take millions of years. It COULD happen overnight.

Looking at all the direct quotes from Jenny Graves, they all seem fine. It's the journalist parts of it that are misleading. These say

Right now, this is all speculative. The Y chromosome is degrading, that much is clear. The future result, on the other hand, is less so. In millions of years, men could simply cease to exist. We could equally see an evolutionary change with an entirely new sex forming.

'Men wouldn't 'simply cease to exist - they would arise through a different deployment of genes on chromosome. And 'an entirely new sex'' is nonsensical.

In fact, with so many humans around the world and the innate weirdness of the Y chromosome, Graves believes that somewhere there could already be a man born without a Y chromosome for the first time.

As for "Graves believes there could already be a man born without a Y chromosome" that's not a direct quote and I'm pretty sure Graves knows that there are such individuals. It's the journalist who is confused.

Thanks for this

[El Pollo Diablo]

Can I ask, if there is an X chromosome with all the male sexual characteristics on it, and the other three chromosomes involved in sexual reproduction are all standard X chromosomes - then functionally, what's the difference between the male X and a Y chromosome? Surely, if men are passing down the male X to their sons as now, won't that see the same slow generational deterioration in the male X chromosome quality over time?

[Grumble]

Can I ask, if there is an X chromosome with all the male sexual characteristics on it, and the other three chromosomes involved in sexual reproduction are all standard X chromosomes - then functionally, what's the difference between the male X and a Y chromosome? Surely, if men are passing down the male X to their sons as now, won't that see the same slow generational deterioration in the male X chromosome quality over time?

Maybe it would even lose one of its four branches

[Allo V Psycho]

Can I ask, if there is an X chromosome with all the male sexual characteristics on it, and the other three chromosomes involved in sexual reproduction are all standard X chromosomes - then functionally, what's the difference between the male X and a Y chromosome? Surely, if men are passing down the male X to their sons as now, won't that see the same slow generational deterioration in the male X chromosome quality over time?

I'm not sure what you mean by 'the other three chromosomes involved in sexual reproduction'?

[El Pollo Diablo]

Sorry, that was badly expressed. So in a couple engaging in a bit of productive how's-your-father, in a world where the Y chromosome has been upgraded to a shiny new X_m chromosome, the woman has XX, the man has XX_m.

Three of those four chromosomes are normal X, one is X_m. Obviously, only two of them are actually involved in any one baby-boffing, but regardless, the X_m remains the only chromosome that can produce males, and will be passed on in that instance. So what's stopping that X_m chromosome getting worse over time, like the current Y one does? Or is that not how it works?

[Gfamily]

Sorry, that was badly expressed. So in a couple engaging in a bit of productive how's-your-father, in a world where the Y chromosome has been upgraded to a shiny new X_m chromosome, the woman has XX, the man has XX_m.

Three of those four chromosomes are normal X, one is X_m. Obviously, only two of them are actually involved in any one baby-boffing, but regardless, the X_m remains the only chromosome that can produce males, and will be passed on in that instance. So what's stopping that X_m chromosome getting worse over time, like the current Y one does? Or is that not how it works?

The X/X_m carries a lot of genes, so any random area of degradation is likely to be generally detrimental rather than gender specific, and thus less likely to be passed on.
I guess

[Sciolus]

The Y chromsome carries the SRY gene, which initiates male sexual development. This can already translocate to another chromosome, and you can get a 46 XX male

Thanks for your educational (to me) post.
At the moment, the XY system means that half of people have one copy of SRY and half of people have no copies (ignoring outliers). What would happen if SRY migrated to a different chromosome, population-wide? In the short term, I think you would find 25% with no copies, 50% with one copy and 25% with two copies, so presumably 25% female and 75% male. I'm not sure how evolutionarily stable that would be, and wonder if we would evolve some other sex-determining mechanism. Biology shows us there are plenty to choose from.

[Allo V Psycho]

Sorry, that was badly expressed. So in a couple engaging in a bit of productive how's-your-father, in a world where the Y chromosome has been upgraded to a shiny new X_m chromosome, the woman has XX, the man has XX_m.

Three of those four chromosomes are normal X, one is X_m. Obviously, only two of them are actually involved in any one baby-boffing, but regardless, the X_m remains the only chromosome that can produce males, and will be passed on in that instance. So what's stopping that X_m chromosome getting worse over time, like the current Y one does? Or is that not how it works?

OK, I understand. Yes, that's right, the new Xm would be as vulnerable as the old Y. But WHY is it vulnerable? Jenny Graves suggests the testicle is a dangerous place to be, but then why is THAT the case? It's certainly an ODD place - why is it outside the body, which creates a hernia hazard for males (and rather unfairly for females too). Yes, sperm are temperature sensitive but why is THAT the case? During embryonic/fetal development, sperm progenitor cells are fine at body temperature, so why do they then develop temperature sensitivity?

It's about 20 years since I did any work in this area, so I looked up the spiny rats. Turns out they didn't translocate SRY as I thought, they have lost it too. But they then upregulate Sox9, which is downstream of SRY, so it has the same effect.


Terao, M., Ogawa, Y., Takada, S., Kajitani, R., Okuno, M., Mochimaru, Y., Matsuoka, K., Itoh, T., Toyoda, A., Kono, T. and Jogahara, T., 2022. Turnover of mammal sex chromosomes in the Sry-deficient Amami spiny rat is due to male-specific upregulation of Sox9. Proceedings of the National Academy of Sciences, 119(49), p.e2211574119.

[Allo V Psycho]

The Y chromsome carries the SRY gene, which initiates male sexual development. This can already translocate to another chromosome, and you can get a 46 XX male

Thanks for your educational (to me) post.
At the moment, the XY system means that half of people have one copy of SRY and half of people have no copies (ignoring outliers). What would happen if SRY migrated to a different chromosome, population-wide? In the short term, I think you would find 25% with no copies, 50% with one copy and 25% with two copies, so presumably 25% female and 75% male. I'm not sure how evolutionarily stable that would be, and wonder if we would evolve some other sex-determining mechanism. Biology shows us there are plenty to choose from.

Yes, it would be fun/complicated, but I don't think you would get one large population with 75% males and 25% females. My guess would be that the new population of XXm would only be viable through evolutionary bottlenecking of some kind, and indeed the spiny rats are in small numbers on a protected Japanese island. It might be a bit more like evolving a new species than having both mechanisms present in one species.