the y chromosome

[cpt.scruffy]

so the x and y divered approx 300 mya.

recombination favours the isolation of the y (male) gene, in non-recombinant areas to support maleness and diversity.
however, along with it, the y gene sufferes gene deletion.
ignore all the above jargon if you wouldn't get it.

essentially, the Y chromosome started off with around 1500 genes, and it's now down to 80. we have 10 million years to go before it self-destructs!

what will happen to men?
the y gene basically activates our male characteristics after birth.
once it's gone, we're done for!
or will we be turtles, and let weather determine our sex for us?

 

[madanthonywayne]

I've heard this argument before and don't buy it. Sure the number of genes have decreased, but natural selection will not allow them to decrease below what is needed for breeding. Any such chromosomes that come into existence will not reproduce!

You might also note that we've become taller, will future generations be ten feet tall?

Straight line projections are not always the best predictor of future events, even when the previous rate of change has been linear. At some point a limit may be reached and your straight line projection breaks down.

For a good example look at Down's Syndrome, or trisomy 21. Why is it the most common trisomy in the population when trisomy is possible with any chromosome? Because most other trisomies are fatal! A fetus with a trisomy affecting a chromosome other than 21 will most likely spontaneously abort.

If the Y chromosome continues to shrink, we will see more sex linked disorders among males. But it will never shrink below what's needed to breed. Sure this may occur in isolated individuals, but they will not breed and will be removed from the gene pool.

 

[cpt.scruffy]

I've heard this argument before and don't buy it. Sure the number of genes have decreased, but natural selection will not allow them to decrease below what is needed for breeding. Any such chromosomes that come into existence will not reproduce!

well, i'm not saying we will no longer be able to breed, hence my use of the turtle. the kangaroo is down to 1 gene. the mole-vole actually has no more y gene. i think what i was told in the lecture was that once the y chromosome self destructs, the x will diverge over time, creating a new y chromosome.

You might also note that we've become taller, will future generations be ten feet tall?

yes, i can see this. however, is it a global phenomenon? is this happening in bangladesh or places of severe poverty? the current growth in height that you see can just as easily be the hormones put into our diet. in addition, our overabundance of food, which we would probably not have in the natural environment. i personally don't know if it is a global phenomenon, but in cases where i have friends from around the world, that's what im thinking about.
i have a friend from bangladesh, who was raised in UAE's abu dhabi.
now, bangladesh has terrible living conditions in comparision to the UAE.
he notes that everyone in bangladesh is shorter than he is, although he is short here in North America. so what gives?

Straight line projections are not always the best predictor of future events, even when the previous rate of change has been linear. At some point a limit may be reached and your straight line projection breaks down.

granted.

For a good example look at Down's Syndrome, or trisomy 21. Why is it the most common trisomy in the population when trisomy is possible with any chromosome? Because most other trisomies are fatal! A fetus with a trisomy affecting a chromosome other than 21 will most likely spontaneously abort.

huh, that's interesting. i'm not sure i'm quite clear on your straight line projection breaking down in relation to this, however.
do you mean the straight line projection would occur with trisomy 21, but the line would break down if a trisomy were to effect any other than chromosome 21?
and i'm not sure what a trisomy is. :bugeye: like 3 of one chromosome?

If the Y chromosome continues to shrink, we will see more sex linked disorders among males. But it will never shrink below what's needed to breed. Sure this may occur in isolated individuals, but they will not breed and will be removed from the gene pool.

studying an isolated individual is not how this sort of study would work!
why would they do that? that's like scientific malpractice, whatever that may be!
it's a population issue. moreover, the loss of the y-chromosome is studied in both humans and animals.
what lies in the future for humans, i'll remain inconclusive, but i think it's quite possible the loss of the y-chrosome may come.

the debate for what will happen is there, and the loss of the male may not even happen. the isolated individuals with no y chromosome may still be males with different attributes that may win the race.

anyway, the y-chrosome is bound to come back over some period of time after it's destroyed. the y-chromsome diverged from the x-chromosome in the first place.

 

[MetaKron]

If a straight line projection says that the Y chromosome will disappear in a few million years, is it also a straight line projection backwards that says that it had all those genes millions of years ago?

 

[cpt.scruffy]

If a straight line projection says that the Y chromosome will disappear in a few million years, is it also a straight line projection backwards that says that it had all those genes millions of years ago?

i would say so, because that straight line projection backwards is something that is seen, whereas a straight line forward may meet something on its way, and thus break its straight line?

 

[madanthonywayne]

the debate for what will happen is there, and the loss of the male may not even happen. the isolated individuals with no y chromosome may still be males with different attributes that may win the race.

The already exists a disorder in which an individual has only one X chromosome. It's called Turner's syndrome and the affected individuals are female.

Turner syndrome is a rare chromosomal disorder of females characterized by short stature and the lack of sexual development at puberty. Other physical features may include a short neck with a webbed appearance, heart defects, kidney abnormalities, and/or various other malformations. Among affected females, there is also a heightened incidence of osteoporosis, type II diabetes, and hypothyroidism. There appears to be great variability in the degree to which girls with Turner syndrome are affected by any of its manifestations.

Turner syndrome occurs when one of the two X chromosomes normally found in women is missing or incomplete. Although the exact cause of Turner syndrome is not known, it appears to occur as a result of a random error during the division (meiosis) of sex cells.

Remember, the defalt condition for humans is female. If the Y chromosome disappears, there will be no males, just sterile, short, sickly females.

 

[cpt.scruffy]

The already exists a disorder in which an individual has only one X chromosome. It's called Turner's syndrome and the affected individuals are female.

word to turner's with the XO chromosome.

but in the case of the self-destruction of the y chromosome, it just means there will no longer be xy's. keep in mind there are no YY combinations.

just XXs. that's the case.

in the mole-vole, it lost the Y, whereas the male genes are connected to another autosome (x).

 

[cpt.scruffy]

whoops you already noted the default condition... my bad

 

[madanthonywayne]

in the mole-vole, it lost the Y, whereas the male genes are connected to another autosome (x).

I've not studied the mole-vole. So it seems you're saying the genes are still there, they've just moved.

It seems a rather dramatic change considering the whole purpose of meiosis is to separate the sex chromosomes.

If the male info is on a normal autosome, couldn't some individuals get two or more copies? In humans, the XYY results in criminals and overly aggressive behavior. I remember reading that the XYY genotype is way over represented in the prison population.

 

[cpt.scruffy]

I've not studied the mole-vole. So it seems you're saying the genes are still there, they've just moved.

It seems a rather dramatic change considering the whole purpose of meiosis is to separate the sex chromosomes.

If the male info is on a normal autosome, couldn't some individuals get two or more copies? In humans, the XYY results in criminals and overly aggressive behavior. I remember reading that the XYY genotype is way over represented in the prison population.

ahah, that's neat. i have never heard of the XYY combination. hm, that's an interesting thought. i've no idea. someone with better knowledge should answer that. i suppose that makes sense if XXY is underdeveloped male features.


there's also theory arguing that there's also a back up code that can recreate the male genes or something. so in the end, we won't lose the y chromosome.


i just rechecked my notes.. and to clarify and directly quote the notes:

the mole-vole has lost its Y, and male genes are connected to another autosome (X), perhaps to start the process over again.

 

[Plazma Inferno!]

In humans, the XYY results in criminals and overly aggressive behavior. I remember reading that the XYY genotype is way over represented in the prison population.

Not neccessarily. Are you Alien 3 fan?

Population with XYY genotype is mostly clumsy with muscle weakness (motoric problems during their life). They have more trouble with learning and language, than with agression.

Truth is that they are prone to be impulsive and hyperactive, but they are aggressive as 46, XY persons. They have normal level of testosterone, which is main factor for aggressiveness (right?).
But it's all individual, as with 46, XY persons.

Other characteristics of XYY genotype are: taller than their relatives, more Acne vulgaris on the skin and somewhat lower IQ than their siblings, but definitely have not mental problems. They have normal sexual development and are able to conceive children (XXY genotype persons aren't).

 

[cpt.scruffy]

Not neccessarily. Are you Alien 3 fan?

Population with XYY genotype is mostly clumsy with muscle weakness (motoric problems during their life). They have more trouble with learning and language, than with agression.

wait, how does muscle dystrophy happen with XYY? why isn't it muscle hypertrophy? i thought weak muscle development happened in XXY.
i never studied XYY, so i'm speculating.

 

[valich]

Do we have any evidence of sexual organisms ever becoming asexual?

 

[cpt.scruffy]

Do we have any evidence of sexual organisms ever becoming asexual?

well metazoans switch between being asexual and sexual.
it's kinda retarded.

an example would be a worm, which is what many believe all animals to come from!

and then you have sexes. xx and xy's in humans, where the y diverges from the x a loong time ago. where researchers believe we had around 1500 genes.
now it's around 80.

and then you look at kangaroo's, which only have one gene left in their y chromosome.

and look further at mole-voles, who have male genes sprouting out to an autosome (x), and the guess is that the y-chromosome is coming back in mole-voles.

therefore, some researchers believe it's a cycle.

so we look all this, and other evidence as well,
scientists end up connecting 2 and 2 together, using further in-depth research to close possible gaps/mistakes that we might make in the loss-of-y-chromosome hypothesis.

 

[Plazma Inferno!]

wait, how does muscle dystrophy happen with XYY? why isn't it muscle hypertrophy? i thought weak muscle development happened in XXY.
i never studied XYY, so i'm speculating.

Not dystrophy, just weakness. They could suffer motoric problems, so they could be little bit slower, but not all XYY persons, of course.
As I said it's individual.

There could be variety of symptoms in 47, XYY, but sometimes they could be hardly recognized, because some males with 46,XY karyotype with somewhat higher testosterone level, could appear as XYY persons.

Otherwise, males with 47, XXY karyotype (with Klinefelter syndrome), have similar symptoms. But also, there are varieties among them. Some of them are slightly gynecomastic, have normal body hair and decent muscle development.
Common for them is lower level of testosterone and sterility.

Also, there is possibility that males with 46, XY karyotype look exactly like males with Klinefelter syndrome, if they have somewhat lower testosterone level.

 

[valich]

No organism today has only 80 genes. You have to attribute this to increased diversity and/or duplication. A defense that the Y chromosome will not go extinct.

 

[Idle Mind]

No organism today has only 80 genes. You have to attribute this to increased diversity and/or duplication. A defense that the Y chromosome will not go extinct.

I think he means that there are 80 on just the Y Chromosome.

 

[Walter L. Wagner]

Right. The Y chromosome started out as an X chromosome with some 1500 genes some 300 mya, but over time reduced to only 80 genes, as it became modified to code for male sexual characteristics.

How the heck does a kangaroo manage with only 1 gene on its Y? Does that mean that the other sex-characteristic genes have translocated to another chromosome, and the sole remaining Y gene is simply an on/off switch?

 

[valich]

This subject is mucher deeper than is presented. I am posting to learn more: not to debate. The SRY gene is what determines the testis. Phylogenetic analysis shows that SOX3 is the gene most closely related to SRY, supporting the hypothesis that SOX3 was the ancestor of SRY. The genes that are being lost are the nonessential genes on the Y chromosome that are non-coding DNA apparently originally duplicated from functional genes on the X chromosome or psuedogenes from it. The essential genes remain but most mutations and phenotype abnormalities seem to be the result of mutations in the SRY gene. This gets very complicated. "It is not known whether there is a predisposition toward the loss of the Y chromosome or it is merely a random event caused by the inherent instability/inability of th XY chromosome pairing." http://jcem.endojournals.org/cgi/reprint/90/4/2429.pdf

""At the observed rate of attrition, the human Y chromosome will be gone in 5–10 million years. This could lead to the extinction of our species or to a burst of hominid speciation....The Y chromosome evolved after the divergence of mammals from reptiles 310 Myr ago. The mammalian Y chromosome is therefore 170–310 Myr old. The origin of Y-borne genes predicts that genes on theY chromosome are all relics of genes that were on the ancient proto-sex chromosome or the added region. They should all therefore have X-borne homologues, whose sequence and function have remained largely unchanged. Most of them do. However, several multicopy testis-specific genes on the Y that appeared to have no X homologue were placed in a discrete ‘Class II’ of male-advantage genes that were acquired by a ‘selfish Y’ and amplified. Two genes, CDYand DAZ, fit this description, being on the Y only in humans, presumably as a result of recent transposition from autosomal homologues....However, X-borne partners have been discovered for at least some genes that are multicopy and testis-specific, such as the candidate spermatogenesis gene RBMY. The distinction between two discrete classes of Y-borne genes also breaks down when other species are considered, because several genes such as ZFY belong to Class I (single copy with X-linked homologues) in humans, but are Class II (testis-specific and multicopy) in rodents. It therefore seems likely that many or most Y-borne genes represent a spectrum of degradationand specialization, from full homology to complete loss. Class I genes are simply those at the beginning of this process. The first stages of degradation are seen in genes (such as RPS4Y) that are partially active. Further degradation left numerous pseudogenes on the Y with active homologues on the X such as STS. The last stage is represented by >1400 X-specific genes whose partners were lost from the Y. Some Class II genes, such as DAZ and CDY, have been selfishly acquired from autosomes, but many Class II genes arose from genes on the proto-XY and acquired a selectable male-specific function. MANY MALE-SPECIFIC GENES WERE AMPLIFIED IN A DESPERATE RACE TO STAY AHEAD OF INEXORABLE DEGRADATION [This I do not understand at all and needs further explanation] They have been retained, at least for a few million years, but could ultimately be superseded. For instance, a putative spermatogenesis gene UBE1Y is Y-borne in mouse and marsupials but not primates." http://biolog-e.ls.biu.ac.il/faculty/wides/80-855/SRYevol.pdf

"The mouse Y chromosome carries 10 distinct genes or gene families that have open reading frames suggestive of retained functionality; it has been assumed that many of these function in spermatogenesis. However, we have recently shown that only two Y genes, the testis determinant Sry and the translation initiation factor Eif2s3y, are essential for spermatogenesis to proceed to the round spermatid stage. Thus, any further substantive Y-gene functions in spermatogenesis are likely to be during sperm differentiation." http://www.genetics.org/cgi/content/full/166/2/901

"Most of the genes on the Y, even those with a male-specific function, evolved from genes now on the X. At the mercy of a high rate of variability and the forces of drift and selection, the Y has lost genes at a rate of 3-6 genes/million years, sparing those that acquired critical male-specific functions. Even these genes have disappeared from one mammalian lineage or another as their functions were usurped by genes elsewhere in the genome."
http://content.karger.com/ProdukteD...oduktNr=224037&Ausgabe=228416&ArtikelNr=63022

"In mammals, sex is determined by an XY male:XX female sex chromosome system in which a male-dominant gene on the Y chromosome (SRY) determines testis formation. Sex chromosomes evolved from an ordinary autosome pair as the Y chromosome was progressively degraded. The Y chromosome has lost nearly all of its 1500 original genes, and those that survived did so because they evolved a critical role in male determination or differentiation. SRY is typical of Y-borne genes. Comparative gene mapping and sequencing shows that SRY arose quite recently as a degraded version of the SOX3 gene on the X chromosome. SOX3 is expressed predominantly in brain, and so is more likely to be a brain-determining than a testis-determining gene. The male-dominant action of SRY may be an illusion, as its structure suggests that it works by interfering with the action of a related gene, which in turn inhibits testis development. This hypothesis can give a good account of how a brain-determining gene acquired a role in testis determination via differential dosage of SOX3. SRY has no central role in sex determination and it can be replaced as a trigger and lost, as have many other Y-borne genes in recent evolutionary history. The absence of SRY in two species of the mole vole (Ellobius) suggests that its useful life is already running out." http://www.publish.csiro.au/paper/RD01093.htm

 

[invert_nexus]

Reduced.
Deletions etc...
For instance, you might recall that thing on the third retinal cone in humans, yes?
The gene for this third cone is on the X chromosome. This explains why males are prone to color-blindness. They have only one copy, and if it's the defective version... than whammo. Color blind.

There a variety of other conditions that are also like this.