Death of Y may spawn new human species

[mr friendly guy]

linky

Death of Y may spawn new human species
Judy Skatssoon
ABC Science Online
Thursday, 10 August 2006

The pending demise of the Y chromosome could give rise to a whole new species of human, a professor of comparative genomics says.

Scientists have been speculating about the demise of the Y chromosome for some years now but Professor Jenny Graves of the Australian National University in Canberra has come up with a bold new twist on the theory.

Graves, who has been working on sex chromosomes in marsupials, will present her theory at the 11th International Congress of Genetics in Brisbane today.

She will tell the conference that new 'male making' genes on other chromosomes could step up to do the job of the Y chromosome's SRY gene, which is the key to making males male.

But this could mean men without Y chromosomes would split off from those with, eventually evolving into a new species of hominid.

"It's quite possible that you could make new hominid species that way," she says.

When two populations become two species

Graves says men without a Y chromosome would be largely infertile. But a small number would reproduce and pass the new sex determining gene to their children.

Eventually the group with the new gene would separate from the Y gene group, potentially evolving into a new species, she says.

"[The two groups] couldn't mate with each other so they'd get gradually different, just like chimpanzees and humans gradually became different 5 million years ago," she says.

"When two populations become two species there's generally there's some sort of wedge driven between them so they can't mate with each other.

"It might be a mountain range ... but it might be something fundamental like the way they determine sex has flipped to some new way."

15 million years and counting

Graves says there are only 45 genes left on the Y chromosome from "a grand total" of 1400.

It also contains a lot of 'pseudo genes', which look like they should work but don't, suggesting they've recently become defunct.

According to her projections the Y chromosome will disappear altogether in 15 million years.

This will occur because unlike the other coupled genes, the single Y chromosome can't recombine with a matching partner and refresh itself.

Mutations will build up and the mutated genes will eventually drop off the chromosome because they no longer perform any useful function.

Graves says this has already happened in the case of the mole vole, an aggressive little rodent that appears male and is able to reproduce despite having lost its Y chromosome.

XX men

Australian researcher Professor Andrew Sinclair, of Murdoch Childrens Research Institute, is researching so-called XX men, or the roughly one in 150,000 men who are born without a Y chromosome.

"What it's pointing to is the presence of new genes we haven't yet discovered to replace the ones on the Y chromosome," Sinclair says.

Alternately, the "volume" of previously existing genes may have been "turned up" in the absence of the Y genes, he says.

Sinclair's team is the first in the world to use new high-density gene chips to examine XX men in the hope of finding out which genes these are.

About 10% of affected men also have a tiny portion of the Y chromosome stuck on their X chromosome which carries across the testis determining gene, he says.

Sinclair says Grave's theory about a new human species could make sense "in a theoretical way" but is unlikely in reality.

"I don't know about a whole new species of human but if you lost the Y chromosome completely males would have to evolve in some way to deal with it," he says.

"If you have males without a Y chromosome I don't think I'd go as far as calling them a new species, but a new type of individual."

[FTeik]

That woman is very optimistic, if she thinks humans will be around that long.

[Nieztchean Uber-Amoeba]

The so-called 'demise of the Y chromosome' is happening right now on such a negligible level, with relatively little actual research done on it, that it may not actually be happening at all.

[Tasoth]

I love when nature shows how thorough it is with back up redundancy among biological species. Also, this is another thing to throw in the faces of creationists because if God created everything, he wouldn't have need to make such redundancy in sex determination because it would never fail.

[Crossroads Inc.]

So just what would physically happen if the "Y" vanished all together.

[Nieztchean Uber-Amoeba]

So just what would physically happen if the "Y" vanished all together.

The Human race is wiped out as no males are boprn into the next generation. Probably there would be a frenzy of cloning research and milking remaining men for their sperm, but it wouldn't be enough to stop most of the world from dying off, after which the level of infrastructure damage from the lack of people to move goods and services would collapse the rather expensive processes of storing sperm and cloning people.

[AMX]

So just what would physically happen if the "Y" vanished all together.

The Human race is wiped out as no males are boprn into the next generation. Probably there would be a frenzy of cloning research and milking remaining men for their sperm, but it wouldn't be enough to stop most of the world from dying off, after which the level of infrastructure damage from the lack of people to move goods and services would collapse the rather expensive processes of storing sperm and cloning people.

Nope.
Apparently you missed the part of the article that mentioned "XX men" - people who are physically male without having a Y chromosome.
You know, what Tasoth meant when talking about redundancy?

Of course, there would be a population decline, as the species switches over from "males have XY" to "males have (any one of the conditions causing XX men"; but we certainly wouldn't die out.

[Spanky The Dolphin]

Wait, what Death of Y?

[Nieztchean Uber-Amoeba]

So just what would physically happen if the "Y" vanished all together.

The Human race is wiped out as no males are boprn into the next generation. Probably there would be a frenzy of cloning research and milking remaining men for their sperm, but it wouldn't be enough to stop most of the world from dying off, after which the level of infrastructure damage from the lack of people to move goods and services would collapse the rather expensive processes of storing sperm and cloning people.

Nope.
Apparently you missed the part of the article that mentioned "XX men" - people who are physically male without having a Y chromosome.
You know, what Tasoth meant when talking about redundancy?

Of course, there would be a population decline, as the species switches over from "males have XY" to "males have (any one of the conditions causing XX men"; but we certainly wouldn't die out.

Double XXs are so incredibly rare that once our infrastructure collapsed from the massive population drop, starvation and exposure would kill most of the survivors who don't know anything about surviving without modern conveniences.

Actually, Man would probably survive. But we'd be very, very fucked.

[Tasoth]

Wait, what Death of Y?

Since the Y chromosome has no other Y to pair up with when fertilization occurs, there's nothing for it to check the sanctity(?) of the genes it carries on it. This allows for mutations that knock out genes to gather on the Y without repair, slowly rendering it a useless chromosome. The long the species goes on, the more degraded it becomes until it is useless for causing a developing to switch from female, which we all our before a certain point in gestation, to male. The article is about how there are other genes that express when this happens and turn an infant into a male without the Y chromosome being present.

[AMX]

Double XXs are so incredibly rare that once our infrastructure collapsed from the massive population drop, starvation and exposure would kill most of the survivors who don't know anything about surviving without modern conveniences.

Actually, Man would probably survive. But we'd be very, very fucked.

Again, nope.
If, by act of plot, starting today, no Y chromosomes could be passed on any more, birthrates would not be affected until the first batch of "Y-less" children reaches adulthood - that's about two decades there during which the problem is blatantly obvious, but has no actual detrimental effect on society.
After the ratio of adult males/females starts to shift, you may see an according drop in births, but only if people value monogamy more than survival; otherwise, the remaining XY men can easily keep birthrates constant for another thirty years or so.

That's half a century to "manufacture" as many new XX men as possible; any first world country that's not hopelessly stuck in "traditional values" should be able to control the impact.

Third world countries would be fucked, of course. No pun intended.

[Tribun]

I think that someone read too much "Y: The last Man".
Otherwise no commant to this pile of mubo-jumbo.

[Molyneux]

...if this is going to take 15 million bloody years to occur, I don't think we have to worry about humanity surviving it. I mean, even a race as stupid as we sometimes are should be able to come up with viable cloning techniques or SOMETHING to allow an all-female race to reproduce by then.

[Admiral Valdemar]

To be honest, I remain thoroughly unconvinced about this doomsaying about the Y-chromosome dying out. We haven't seen this happen in any other mammalian species or species with two sexes of our age, or even older. It sounds like someone wants the upcomoming movie The Children Of Men to be real.

[Wyrm]

On the doomsaying of the Y... who the fuck cares? As long as humanity has a way of making boys and girls that works, whether the Y stays or goes is academic. Personally I'm banking on advanced genetic engineering of custom sexes made-to-order, which will make the survival of the Y moot, and make it a very sexy time to be alive.

[Setesh]

Wait, what Death of Y?

Since the Y chromosome has no other Y to pair up with when fertilization occurs, there's nothing for it to check the sanctity(?) of the genes it carries on it. This allows for mutations that knock out genes to gather on the Y without repair, slowly rendering it a useless chromosome. The long the species goes on, the more degraded it becomes until it is useless for causing a developing to switch from female, which we all our before a certain point in gestation, to male. The article is about how there are other genes that express when this happens and turn an infant into a male without the Y chromosome being present.

Its a load of horse-hockey.

As a result of this process, for humans, 95% of the Y chromosome is unable to recombine, and Y chromosome contains only 78 working genes [2] versus about 1000 genes for X chromosome. For some other animals, the degradation of Y chromosome is even more severe. For example, the Y chromosome in kangaroos contains only the SRY gene.
[edit]

Gene conversion

In 2003, researchers from the Washington University discovered another process which may slow down the process of degradation [3]. They found that human Y chromosome is able to "recombine" with itself, using palindrome base pair sequences. Such a "recombination" is called gene conversion or "recombinational loss of heterozygosity" RecLOH.

In the case of the Y chromosomes, the palindromes are not junk DNA; these strings of bases contain functioning genes important for male fertility. Most of the sequence pairs are greater than 99.97 % identical. The extensive use of gene conversion may play a role in the ability of the Y chromosome to edit out genetic mistakes and maintain the integrity of the relatively few genes it carries.

Findings were confirmed by comparing similar regions of the Y chromosome in humans to the Y chromosomes of chimpanzees, bonobos and gorillas. The comparison demonstrated that the same phenomenon of gene conversion appeared to be at work more than 5 million years ago, when humans and the non-human primates diverged from each other.

This recombination phenomenon RecLOH is also observed in Genetic Genealogy when multicopy Y-STR markers located at adjacent palindromic arms change from different repeat counts to twin alleles of equal length. Often 2, 3 or more Y-STR markers are involved in the same recombinational event and change to twin alleles at once.

[Spin Echo]

Unless she's dug up some sort of new evidence to the contrary, I thought that it was well proven the Y chromosome is not disappearing. The paper on the work can be found inNature.

A quick summary in the abstract:

The human Y chromosome, transmitted clonally through males, contains far fewer genes than the sexually recombining autosome from which it evolved. The enormity of this evolutionary decline has led to predictions that the Y chromosome will be completely bereft of functional genes within ten million years1, 2. Although recent evidence of gene conversion within massive Y-linked palindromes runs counter to this hypothesis, most unique Y-linked genes are not situated in palindromes and have no gene conversion partners3, 4. The 'impending demise' hypothesis thus rests on understanding the degree of conservation of these genes. Here we find, by systematically comparing the DNA sequences of unique, Y-linked genes in chimpanzee and human, which diverged about six million years ago, evidence that in the human lineage, all such genes were conserved through purifying selection. In the chimpanzee lineage, by contrast, several genes have sustained inactivating mutations. Gene decay in the chimpanzee lineage might be a consequence of positive selection focused elsewhere on the Y chromosome and driven by sperm competition.

As I suspect the Nature site will require a subscription to read, the gist can be found here