Biologists Debunk the "Rotting Y Chromosome" Theory

I dunno... by owenferguson · 2012-02-22 13:29 · Score: 4, Funny

I tend to shed my genes all over the place ... on the floor, in some Kleenex, in dirty socks...

Re:I dunno... by MagusSlurpy · 2012-02-22 19:36 · Score: 4, Funny

My roommate's g/f's dog has recently started to come visiting with her (joy!), and he likes to go digging through trash cans for those stinky Kleenex and then eat them on their bed. It's pretty goddamn hilarious.

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Both sexes are valuable by Anonymous Coward · 2012-02-22 13:30 · Score: 5, Interesting

While our Y chromosome may make us (men) more susceptible to genetic diseases, it also allows for more rapid adaptation and spread if a mutation is beneficial. I certainly wouldn't want it to go away.

Re:Both sexes are valuable by Darinbob · 2012-02-22 13:49 · Score: 5, Interesting

Except that they were talking about the Y chromosome. The problem with it is that it doesn't get combined with genetic material from the mother, it's passed on as-is. So over time it can degrade due to mutations, and it has done this in the past. However natural selection is strong enough to maintain it.
Re:Both sexes are valuable by interkin3tic · 2012-02-22 14:28 · Score: 4, Informative

Another problem with the y chromesome is that it's not fully redundant with the x chromesome. There are plenty of important genes on the x chromesome that are not duplicated on the y chromesome. There are some diseases which mainly show up in men because females can be heterozygous for it, have one faulty copy but one good copy and be okay. Men on the other hand are hemizygous for genes on the x chromosome. If we get a faulty copy, that's it. We have the disease.
Re:Both sexes are valuable by reverseengineer · 2012-02-22 15:23 · Score: 5, Interesting

Well, there's no specific reason to favor the XY system of sex determination over some alternative arrangement, like the ZW system in birds (females are ZW, males are ZZ). In that case, the Z chromosome is larger and has more genes than the W. On the other hand, there's really no evidence to suggest that the XY system is any worse than the alternatives, or at least worse enough to support some sort of changeover (or lead to the extinction of placental and marsupial mammals). It does make sense to let Y "rot" to a certain extent: letting Y "cross over" with X is hazardous. It leads to the possibility of producing gametes that contain X chromosomes with male-sex determining genes, and gametes that contain Y chromosomes that lack those male-determining genes. It is to the system's benefit that X and Y are completely non-homologous, even factoring in the problem of X-linked diseases. It's theoretically possible that the function of Y could be captured in a single gene. However, chromosomes are also physical structures that have to be able to be manipulated by the machinery of the cell. It's likely that there is a minimum size for that to be done without high risk of error, which means that Y is safe.... for now.

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"FDA staff reviewers expressed concern about the number of patients who were left out of the study because they died."
Re:Both sexes are valuable by __aaltlg1547 · 2012-02-22 15:59 · Score: 4, Insightful

Bingo!
Humans would have to evolve a new mechanism of determining sex before the Y chromosome could lose its function.
It's always been obvious that the disappearing Y was bullshit. What we have is a selection pressure that shrinks the Y down to its essential core, which apparently is not much less than the 19 genes and other noncodong DNA it carries in humans.
Re:Both sexes are valuable by Darinbob · 2012-02-22 17:58 · Score: 4, Interesting

I think sometimes there's a misconception of natural selection. All traits and features from big to tiny are not necessarily selected for. Sometimes there are mistakes. Sometimes there are things that just happen without evolution being the answer. I see this especially in the social sciences, and I've heard things like "what is the evolutionary reason for having grandmothers" which may not even have a reason other than mothers not dying or losing maternal instincts. But people assume there must be an "evolutionary reason" too often. Another faulty thinking I see sometimes is the assumption that evolution leads to more advanced life forms and that nothing ever goes backwards (as in the saying "more evolved than that").
So in this case, my answer is that natural selection may not have favored the shortening of the Y, it just happens and it's not perfect and entropy is winning. Sometimes mutations are mistakes and are not weeded out, they're neither harmful nor beneficial and they don't degrade chances of reproducing. For instance there's likely no evolutionary advantage to hemophilia and it's more likely it's just a defect that pops up now and then; maybe it'll diminish over the eons.
Putting in a religion metaphor, I've seen people who want to portray god as a micro-manager so that anything that happens must be caused directly by god. But this is a rather naive theological stance that ignores things like free will. So on the evolutionary side I see the same thing, people wanting to treat evolution as a micro-manager.
Just my evolutionary pet-peeve...
Re:Both sexes are valuable by ArcherB · 2012-02-22 18:24 · Score: 4, Funny

The comments made me think of this: http://www.psy.fsu.edu/~baumeistertice/goodaboutmen.htm . The changing roles of the sexes and modern technology are causing people to honestly ask the question, what are men FOR? As I look back on 50 years of life and 35 years of dating/interacting with females, I wonder too.
We go to work day in and day out and pay the bills while our wives stay at home, watch daytime TV and talk us into getting a housekeeper to come over twice a week.
You know, because we are the smart ones.

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Re:Both sexes are valuable by reverseengineer · 2012-02-22 18:31 · Score: 5, Informative

Crossing over is normally a beneficial practice for chromosomes, and is a key advantage for sexual reproduction. See Muller's ratchet for the case of deleterious effects piling up in organisms who do not use recombination to shuffle around their genes. Therefore, it generally makes sense for chromosomes to pair up, so that at each generation, offspring get a mix of ancestral genes rather than a perfect (aside from mutation, of course) clone of a chromosome from parent's set. Being able to swap homologous genes dramatically increases the diversity of offspring. The X and Y pair is an exception because it would be a problem for recombination to occur. The genes on Y are supposed to be unique to males- if some regions of Y containing them recombined with X, those male-development specific genes could be traded away in exchange for nothing, likely leading to sterile offspring. Therefore, it has been to the advantage of XY-determination organisms to have X and Y as different as possible so that there is basically no recombination. The drawback is that Y doesn't get to recombine with anything (X can still crossover with another X), so a son's Y is essentially his father's Y and grandfather's Y, though with whatever errors have accumulated. This has led to a pruning of genes on Y over time- it appears from this paper that this deletion will not necessarily go to nothing, and that a "minimal Y" may be stable for many millions of years. It does however underline that the X/Y pair is a special case, that the endpoint of the asymmetric relationship that they have is for one chromosome to dwindle to a single purpose. The Y chromosome has 19 genes: X has around 2000.

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"FDA staff reviewers expressed concern about the number of patients who were left out of the study because they died."
Re:Both sexes are valuable by Anonymous Coward · 2012-02-22 18:53 · Score: 5, Informative

Once again with the subject of genetics on Slashdot, we have a shocking level of confident ignorance on display (aided and abetted by the equally clueless moderators).
Please, evolution is not synonymous with natural selection. If all you know about genetics is what you learned in Biology 101, perhaps supplemented by a Dawkins book, you're missing out on most of the picture.
The degeneration of the Y chromosome was made possible by the lack of recombination along most of its length (Muller's ratchet/Hill-Robertson effect), which allowed the combined effects of mutation (including deletions) and genetic drift (which is much stronger on the Y due to there being 1/4 the number of Y chromosomes in a population than a given autosome) to very slowly truncate it. There's really no need to invent post-hoc selective stories to explain this; it's all pretty basic stuff.
Of course, you are correct that this doesn't mean that males would (or could) go extinct if the Y somehow did disappear. No competent scientist would ever claim this; most likely the sex-determining genes would move to other chromosomes.
Summary of this story in Nature
The origins of genome complexity

Wanted to buy... by Sasayaki · 2012-02-22 13:34 · Score: 4, Funny

... go-forward time machine. That way, when Sally McKnight in high school told me, "No way, not if you were literally the last man alive", I can finally test this theory!

I'm not getting absolutely no sex because I'm a hideous subhuman monster, physically and emotionally... no. I'm doing it for SCIENCE.

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Seems like a non-issue either way by alvinrod · 2012-02-22 13:39 · Score: 4, Insightful

It really seems like a non-issue regardless of whether or not the Y chromosome is "rotting." Evolution moves slowly enough that by the time it would become an issue, humans will probably have learned enough about genetics to prevent it from happening if necessary. The other alternative is that we decide it's a good idea and speed the process up by a lot.

Re:Seems like a non-issue either way by John+Hasler · 2012-02-22 14:44 · Score: 5, Funny

> ...evolution will see that...
Don't anthropomorphize evolution. It doesn't like that.

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correct me if I'm wrong by viperidaenz · 2012-02-22 13:43 · Score: 4, Insightful

But the Y chromosome evolved because sexual reproduction has advantages over asexual reproduction. Until that is nolonger true I can't imagine Y going anywhere.

Re:correct me if I'm wrong by samoanbiscuit · 2012-02-22 14:55 · Score: 5, Informative

No, the XX/XY system of sex determination is just one of the many types used in nature, mostly by mammals. Some animals use the XX(female)/X0(male) system, like ants and bees, while reptiles, birds and some other use the ZZ(male)/ZW(female) system. As you can see, in birds and reptiles (not crocodilians or turtles those have a temperature based sex determination mechanism) the ZZ chromosome configuration (the default) is male, while the ZW configuration causes female development. However, back to the disappearing Y chromosome, it is the fastest mutating chromosome in the human genome (and in all mammalian genomes) because it does not recombine with an analogue chromosome, the way two X chromosomes would. However, just because genes are "lost" does not mean it is shrinking, and research stated here shows it to be the case.
Re:correct me if I'm wrong by Michael+Woodhams · 2012-02-22 15:40 · Score: 5, Interesting

They Y chromosome not only evolves fast because of lack of recombination, but also because sperm are very many more cell division generations away from the original copy (fertilized ovum) than ova are. The Y chromosome spends 100% of its time in males, normal chromosomes 50%, X chromosomes 33.3%.
Ref: "Male-Driven Sequence Evolution", pg 225, "Molecular Evolution" by Wen-Hsiung Li (1997).

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Of course by aBaldrich · 2012-02-22 13:43 · Score: 4, Insightful

Suppose that someone inherited from his father an Y-Chromosome without the "Manliness Gene". Then he would not have a functioning reproductive system and leave no offspring. The "Manliness Gene" can be lost by a random mutation, but the mutation will never be carried on to the following generation, unless a new sex-determining mechanism already exists.

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In soviet russia the government regulates the companies.

Why would anybody think otherwise? by Rich0 · 2012-02-22 13:44 · Score: 5, Interesting

So, genders have been around for hundreds of millions of years - why would anybody think that evolution would suddenly make them go away?

In humans it probably doesn't make so much sense to have lots of sex-linked characteristics, so it makes perfect sense that the contents of the Y chromosome would dwindle over time to just the minimal set of genes necessary to confer gender. After that there should be strong selective pressure to conserve things.

Suppose for the sake of argument somebody is born with a Y' chromosome that doesn't confer maleness. Either they'll have non-functional reproductive organs, or functional female ones. In the former case they're an evolutionary dead-end. In the latter case and they reproduce with an XY man then 25% of their children will be normal XX females, 25% will be Y'Y offspring that won't make it to birth lacking an X chromosome, 25% will be normal XY males, and 25% will be XY' like the mother. So, in 75% of those cases the Y' chromosome is lost. And all that assumes that there aren't any deformities/etc that make reproduction less likely. I can't see how such a situation could ever become dominant. It would likely reach some low frequency equilibrium even if not harmful.

The fact that it hasn't already happened makes me think that it is not likely to do so.

Re:Why would anybody think otherwise? by FrootLoops · 2012-02-22 16:56 · Score: 5, Informative

It's worth noting that conditions apart from standard XX female and XY male do occur in humans:
Turner syndrome: usually, single X chromosome, no second X or Y. Creates females who are almost always infertile with varying physical problems. Incidence is around 1 in 2000 to 1 in 5000 (phenotypic) females.
Triple X syndrome: XXX chromosomes. Makes females with essentially no physical differences from XX females (including reproductively). Incidence: 1 in 1000 females.
Klinefelter's Syndrome: XXY chromosomes. Produces sometimes-infertile males, sometimes with developmental problems. 1 in between 500 and 1000 males affected.
XYY Syndrome: XYY chromosomes. Almost no physical differences with XY males (slightly taller). 1 in 1000 males.
XX Male Syndrome: XX chromosomes. Produces always-infertile males who usually appear to be XY males. 4 or 5 in 100,000 people.
Swyer Syndrome: XY chromosomes. Produces females without developed gonads, though a developed uterus may be able to carry another person's embryo.
The above is only a partial list. There are quite a few related conditions that fall under the general heading of "Intersex" (sometimes you see the acronym LGBTI; that's the I). They vary widely from producing (some type of) hermaphrodites to causing a large number of non-standard sex characteristics. From the article,

According to Fausto-Sterling's definition of intersex, on the other hand, 1.7 percent of human births are intersex.
and

Between 0.1% and 0.2% of live births are ambiguous enough to become the subject of specialist medical attention, including surgery to disguise their sexual ambiguity.
To give a very approximate comparison (these numbers vary a lot by region, time period, and definition), around 1% of the population is bisexual, and around 5% is gay. It's perhaps even more difficult to get an accurate transgender incidence number; I've seen between 0.2% and 0.003%. Those who get sex reassignment surgery are in the minority. (There's a lot more to gender than the type of gonads you have, and female-to-male surgery isn't terribly effective.)

link to the source, please by rritterson · 2012-02-22 13:47 · Score: 5, Informative

Not like I love the Nature Publishing Group (NPG) very much, but let's link to the source to help give the original authors credit. (Which, as far as I can tell, the medical daily article doesn't even do!)

Here is a link to the original paper

For those who aren't molecular biologists or geneticists, here is a link to the Nature news article on the scientific paper

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AUWYHSTOT (Acronyms are Useless When You Have to Spell Them Out Too)

Re:Time scale by macraig · 2012-02-22 13:49 · Score: 4, Interesting

That divergence might occur upstairs between the ears. Some groupings of autistic traits seem to be early precursors of that divergence. Call it a disability if you must, but there's gold in them genes for some folks who get the right combination.

Re:Time scale by artor3 · 2012-02-22 14:26 · Score: 4, Informative

Autism is not the superpower that many people make it out to be. You only see the high functioning autistic people. There are a great many who cannot even communicate above an infantile level. Many also suffer from severe OCD. These people need constant care throughout their lives. The brilliance aspect is only found in a small percentage of autistic people, and I've never seen a conclusive study showing that brilliance is any more common among the autistic than it is among "normal" people. It may be that it is simply more noticeable when someone who's autistic has some great talent.

Some women think... by gstrickler · 2012-02-22 15:07 · Score: 4, Funny

...the Y chromosome is already rotten.

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Re:Time scale by artor3 · 2012-02-22 15:14 · Score: 5, Insightful

If "the right combination" is intelligence + virtually no trace of autism symptoms, then why not just take the intelligence part and leave off the crippling disability? Autism is not a prerequisite to high intelligence. There are plenty of truly brilliant people out there who aren't autistic at all.

I used to work in a school for autistic children. I was just the IT guy, but I was in the classroom at times and saw how hard the kids had to work to grasp things that most toddlers can do intuitively. I think it's unfortunate that when kids like that overcome their illness and do great things, people think "Wow, he sure benefited from those genes" instead of "Wow, that guy must have worked really hard to become so brilliant despite his disability."

Re:Time scale by __aaltlg1547 · 2012-02-22 16:30 · Score: 4, Informative

I have yet to see any version of autism that confers any reproductive advantage. All of them I have met have been at a moderate to severe reproductive disadvantage.

Re:Y ain't going' nowhere - makes testes by reverseengineer · 2012-02-22 17:32 · Score: 4, Informative

It appears to have already happened in a few species; as the Nature News article notes, a few rodents have lost their Y chromosome completely. These remain capable of sexual reproduction and also remain differentiated between male and female. In some cases, this was the result of a permanent translocation of the SRY gene to another chromosome- either Y or a somatic chromosome. In some cases, SRY is completely lost, and different genes are used for sex determination. There's really nothing extraordinary about SRY itself, a gene thought to be an accidental duplication of an existing gene on the X. It may well be the case that how an organism determines its sex simply doesn't matter enough; there just has to be some consistent system that allows for propagation of the species. There's a wide variety of successful systems out there already coexisting, and given millions more years, undoubtedly more systems would pop up. In the case of the Y chromosome, however, it was not certain that the system could reach a stable equilibrium at all- it has lost over 96% of its genes in the course of its existence, and it faces an essential problem: the long-term selection to protect reproduction by isolating itself from recombination with X also increases its vulnerability. Ironically, the Y chromosome is itself "asexual" in a way- it passes from father to son through generations without being modified by recombination. Errors tend to accumulate, deletions cannot be replaced- it's called Muller's ratchet. Eventually, XY organisms would need to make alternative arrangements or go extinct.

It would appear, however, that Y chromosomes are a bit more robust than originally thought, and may be able to continue at their present level of basic function for tens of millions of years more. Just as my own thought, one reason for this may be the presence of genes on the Y which are necessary for sperm production. A transition to another form of sex determination would require those genes to be either moved or their functionality replaced elsewhere; otherwise any Y-less males would be azoospermic and therefore the new system wouldn't get passed on.

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"FDA staff reviewers expressed concern about the number of patients who were left out of the study because they died."

Never understood that concern by Arancaytar · 2012-02-22 18:07 · Score: 4, Insightful

What is so worrying about a chromosome becoming smaller over millions of years? If any of the genes that were on it were vital to humans, we wouldn't be here (or rather, they wouldn't have disappeared, since their absence would have been selected against). And what's with the extrapolation - can you really take a past evolutionary trend and use it to project future changes?

If that worries you, how about this: Within a much smaller time frame, our fur has disappeared, our bones and skin have become thinner and our brains have grown. If that trend continues, then eventually we'll have no bones or skin, and our brains will be too big for our bodies to carry.

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Biologists Debunk the "Rotting Y Chromosome" Theory

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