In a brief snippet of an interview I saw with Maureen Dowd she claimed, apparently seriously, that the Y chromosome has been shedding genes and that males will be extinct in several hundred thousand years.
Science? Whooshed?
Then what? Parthenogenesis?
Although, I suspect she wasn’t serious.
Considering that one male is sufficient to impregnate hundreds of females; if anything the hardiest males will be able to pass along their hardy genes. Men with weaker Y chromosomes, whatever the heck that means, will die off and their hardier cousins will be naturally selected.
She seems to have missed a discovery made not too long ago. Read the section on Y Chromosome Repair
Or here’s one from the Whitehead Institute. Just trying to find one from an .edu site.
Interesting stuff. Especially this from the latter site:
“Through sequencing the Y, the Page lab and collaborators at Washington University School of Medicine in St. Louis discovered that many of its genes were located in palindromes—long stretches of DNA letters that read the same forwards and backwards. By folding into a hairpin, the authors suggested, a gene might then swap the appropriate genetic material with itself. This demonstrated a process for the Y chromosome to maintain its integrity despite lacking a mate.
However, there is another region of the Y, called the “X-degenerate” region, where the genes are not situated in palindromes.
“The genes in the palindrome region are primarily sperm-producing genes, and most other genes unique to the Y aren’t located there,” says Jennifer Hughes, a postdoctoral scientist in Page’s lab and first author on the paper. These other genes have no obvious means for self-repair. Because of this, many proponents of the “Y’s demise” theory remained undaunted.”
The theory that I’ve heard is that the Y chromosome is “eliminated” on a fairly regular basis. In essence, some female produces X chromosomes that can supress the Y, producing all female offspring. More and more such females are produced, until eventually one of the remaining males happens to be born with a Y mutation that can overcome the Y suppressor; naturally, this male and his descendents become the future fathers of the species, and the old Y goes extinct.
I see I’m going to be busy! Maybe I should finally spring for one of those Liberator pillows…
As I understand it, this is a bit different from the ‘Y degeneration’ theory, which might be what Ms. Dowd was addressing.
The degeneration theory basically says that, for reasons relating to meiosis and chromosome pairing that I won’t go into here, there’s a tendency for Y chromosomes to gradually lose all their genes except the one gene that serves as a switch to turn on maleness. All the genes that actually do the work of making a male will be on other chromosomes; they just won’t turn on until they get the signal from the male gene on the Y.
Then at some point, by random mutation, in one animal another chromosome - say #17a out of the 32 pairs – gets the male signal gene. Now there are two kinds of males : the Y males, and the 17a males. The 17a males have a slight advantage (because they have two copies of the X chromosome) so eventually, there aren’t any more Y males, and the 17a and 17b chromosome pair are the new sex chromosomes.
At this point, the same meiosis reasons start making the new 17a chromosome start losing genes, until it’s so degenerate it looks like a Y compared to the X of a normal chromosome. And the cycle continues.
Note that nothing about this is particular to humans – the same process should be happening for almost any organism with well defined males and females.
So the bottom line is that, yes the Y chromsome is shedding genes, but that just means that at some point (way, way, way down the road), some other chromosome will be the one that signals male or female. It doesn’t mean that males are ‘going extinct’ or anything.
And for humans, this is far enough in the future that I expect by that point humans will be able to control genetic material enough to head it off.
I don’t get this. Human males aren’t unique amongst mammals, all mammals suffer form this same ‘flaw’. Yet no mammal has yet produced anythingother than an XY male. The generation time for a mouse is about 5 weeks. The generation time for a human is at least 13 years. That means that mice are running about 135 times faster than us WRT this ‘problem’.
If males are ever going to vanish it is highly unlikley it will happen within the human lineage first. When we see this process starting to affect the rapidly reproduciing mammals we may have some evidence. Untilthen it’s essentially baseless speculation in a field that we really know very little about.
I don’t get this. Human males aren’t unique amongst mammals, all mammals suffer form this same ‘flaw’. Yet no mammal has yet produced anythingother than an XY male. The generation time for a mouse is about 5 weeks. The generation time for a human is at least 13 years. That means that mice are running about 135 times faster than us WRT this ‘problem’.
If males are ever going to vanish it is highly unlikley it will happen within the human lineage first. When we see this process starting to affect the rapidly reproduciing mammals we may have some evidence. Untilthen it’s essentially baseless speculation in a field that we really know very little about.
So like, if Humans lose the Y…are we then a different species? Is it conceivable (heh) that some guys will be old fashioned XY males while other sperm producers will be XX males (assuming there’s a mechanism on one of the other chromosomes to flip on the male junk factory)? Or are we staring down a situation where humans become all wimmin with no natural means of reproduction?
off to the kitchen to start filling up freezer containers
Actually they are pretty much the same theory up until the resolution ( I didn’t mention that the Y had degenerated ). One version says the Y mutates; the other, some random chromosome. I think the version I mentioned is more likely, as I think that a mutation to let the “switch” on the Y work again is likely to happen faster than a more radical one on another chromosome. That also mitigates Blake’s objection.
Well the book I read that mentioned the theory claimed it was a likely driver of speciation ( and no, I can’t remember the title ).
I said ‘hardy’, not ‘har-dee-har’.
As an afterthought, the XY structure isn’t limited to humans, is it? Doesn’t every mammal (as well as bird and reptile) have a similar system in place? If the Y chromosome is a dead end, shouldn’t a species with a much faster reproduction cycle have demonstrated it by now? Seems to me that long before humans go all-female, every other mammal species will go first. When tomcats get harder and harder to find, I’ll be concerned.
Gee, I wish I’d said that. :wally
But the same structure doesn’t apply to birds and reptiles. Birds run exactly the opposite system, essentially XY females and XX males. Reptiles do all sorts of funky stuff and often gender is determined by environment long after fertilasation.
Well, that only proves that complete harmony with one’s environment is not critical to survival.
Or evidence of independent development, whatever.
IIRC In fruit flies, there were some long and bizarre combinations. Any individual with a Y was male. The textbook gave the example of a male who was XXYYY
Inigo I’d think a change that major would be a new species. I suggest the scientific name Homo MCA
The XY system isn’t unique to humans, but many other animals have very different systems for sex determination. Some reptiles, like aligators, have their sex determined the ambient temperature during a critical period of embryonic devolment, not genetics. Chicken males are homozygous for sex chromosomes (the equivilent of XX) while the females are hetrozygous (the equivilent of XY). Some other animals, some insects for example are “male” by virtue of being unfertilized gametes. Imagine if a woman just gave birth every year. If she gets fertilized, it’s a girl. If she doesn’t, it’s a boy. There’s some species of communal insect, and I think it’s a type of termite, that uses that system. Some species social species of fish will change from female to male while they’re adults, if the density of the male population drops.
In other words, just think about how complicated the door signs would be for the bathroom in the bars at Mos Eisley.
Maybe we could move to a system like TheLeft Hand of Darkness by Ursula K. LeGuin where everyone takes turns, alternating male and female.
I so misunderstood the thread title when I first looked at it.
I don’t remember anything in the book indicating that Gethenians alternated sex in kemmer. Every kemmer could go either way