All men are part of a PURE GENETIC ELITE, says geno-science bloke According to a new research from genetics gurus, the Y chromosome that all men carry is not at all hobbled by its missing bit. For those who don't know, men carry the XY chromosome pair, while women carry two X chromosomes. The bloke-osome is thought to have evolved from the X, with bits dropping off during 300 million years …
Saying that "What the boffinry gang found was that the human Y had shed just one ancestral gene over the past 25 million years." could also mean that men haven't evolved one bit for 25 million years and are still simian brutes at heart..... which would confirm the gut feelings of many women :-)
If it takes 25m years to change one gene (and that is a loss of genetic material), how long does it take to gain genetic information?
4bn years at one loss per 25m years gives us time enough to lose 160 genes which isn't anywhere near enough to go from 600 female to 19 male, without even beginning to contemplate going from zero to the 600 female genes.
That's the whole point of the article.
The time it takes to change one gene gets longer if the gene is more important, because mutations to important genes are very likely to kill or cripple the individual, preventing the mutation from spreading.
25m years is a pretty long time, even for evolution; the fact that it took that long to change one gene in Y is a fairly strong indicator that all the genes left on Y are the really rather important ones. Most of those 600 genes in X have probably been evolved away much faster because they weren't needed (or, more likely, because the single copy in a male's single X was sufficient).
Studies like this one are actually strongly backing the theory of evolution.
You might be tempted to think of the rate of loss as linear, but that actually doesn't make sense (or, as you rightly note, fit the data). The simplest model that fits the available data is that the rate of decay was initially exponential (like radioactive decay), and then stopped as the surviving set of genes were winnowed down to small set of elite genes each too important to lose.
For a thorough discussion of modeling Y chromosome decay from first principles, see Doris Bachtrog's excellent article in Genetics: http://www.genetics.org/content/179/3/1513.full
For the reasons why we think decay is best modeled as exponential decay to a constant baseline, see Figure 4 of this paper (with comparison to linear and simple exponential models). As well as Jenn Hughes' 2102 Nature paper with a more limited comparison of human, chimp, and rhesus Y chromosomes: "Strict evolutionary conservation followed rapid gene loss on human and rhesus Y chromosomes"
This is only because women never throw anything away. My missus has a room full of clothes she can't get into, handbags loaded with keys that don't fit anything, boxes of VCR tapes that are unplayable and the list goes on. 600 sounds about right as a count of her jeans too.
".... could also mean that men haven't evolved one bit for 25 million years....." Alternatively, it could also suggest that females are just so broken that evolution has spent 25 million years tinkering with the build and still can't get it right. After all, which of us gets PMT?
Most blokes I know do - every fucking weekend during the footie/rugger/cricket season(s)… Pre Match Tension and, if they lost, Post Match Tantrum… not to mention Ref Rage/Ump Hump…
This is the reason I'm currently single (and remaining so…). When my uncle's watching Yorkshire - and they're losing - it's like being in the same room as Geoff Boycott (only with MUCH choicer language…).
After what WE have to put up with from some of you, the fact that you have to cope with us getting a bit tetchy once a month…
I REALLY don't think you've any right to complain…
The Y chromosome isn't standing still, it is adding new genes too. See my colleague Jenn Hughes' 2010 Nature article: "Chimpanzee and human Y chromosomes are remarkably divergent in structure and gene content"
What we show in this study is that in the Y chromosome has also been able to hold on to some of the ancestral genes that it started out with, and that these survivors are a special subset of those ancestral genes.
The sex chromosomes of birds (referred to as Z and W) work the other way round to the mammalian XY system. So male birds are ZZ and females ZW, with the ovum rather than the sperm determining the sex of the offspring.
This enables female Cuckoos to carry specific information about egg colouration on their W chromosome, so a female cuckoo raised in a parasitised Reed Warbler nest will lay eggs only in Reed Warbler nests and not in those of Meadow Pipits or Dunnocks (also parasitised by Cuckoos). Whereas male Cuckoos can mate with any female Cuckoo, so there are effectively multiple distinct subspecies of female, but only one of the male.
This is well described by Dawkins in Unweaving the Rainbow and The Extended Phenotype.
* For some sufficiently small value of 'interesting'.
"What do you expect from a bunch of bloody dinosaurs?"
Longer life expectancy than mammals of equivalent mass - check
More efficient brains than mammals weight for weight - check
Better colour vision than mammals - check
African Grey parrots and jackdaws are particularly intelligent and long lived. We're extremely fortunate that birds don't have a pair of limbs with opposable thumbs, or we'd be the threatened species by now.
You forgot more efficient lungs.
But ultimate brain power, mammals come top, great apes, cetaceans, even some carnivores.
Put together top mammal brain, some of the better mammal COLOUR vision, but more importantly the visual cortex to process it, and of course hands, humans will remain top. An I think we will remain at the top unless we wipe ourselves out.
"We're extremely fortunate that birds don't have a pair of limbs with opposable thumbs, or we'd be the threatened species by now."
Now I wouldn't be too sure of that one (a quick google will give you some interesting answers... though I suppose they are still not opposable digits...).
"Out of curiosity, do you have to sleep on the sofa very often?"
Geneticists have speculated for some time by that there is indeed a gene found on the short arm of the Y chromosome that allows the human male to sleep in restricted spaces without getting a crick in his neck.
It appears to be linked to an as yet unidentified gene that allows the male to filter out higher pitched vocal sounds when attempting to watch sport, as well as being associated with a mutation that causes an awkward delay when responding to the question 'Does my bum look big in this dress?"...
I read that the boffin had also found the same X in Platypus. This showed that it had endured for a looong time.
New movie plot? Man gets bitten by radioactive Platypus, grows poisonous barbs on his heels and starts laying eggs. I want Steven Segal in the lead as only he could express the subtle emotions of the role.
Steven Segal would be an excellent choice.
Sadly, the Platypus X chromosomes and Y chromosomes (that right, plural, they have 5 of each) turned out to be unrelated to the XY pair found in marsupials and placental mammals. See: http://link.springer.com/article/10.1007%2Fs10577-007-1185-3
I don't think it was testosterone as such. It was a particular gland in the brain which is enlarged in males which made us more susceptible to heat changes etc. There's also another theory that goes by evolution, wherein men tended to be the hunter gatherer and wound up dying young, not needing to build up their immune system, while women were left behind in the cave to care for the germ bags. As women grew older the grandmothers also helped raising the germ bags, perhaps even having more, slowly passing on an improved immune system.
The termerature receptor thing also explains why women can bathe in water hot enough to boil an egg while men have to have their bath luke warm at best.
http://www.telegraph.co.uk/health/healthnews/7505207/Man-flu-is-no-myth-as-scientists-prove-men-suffer-more-from-disease.html
http://www.telegraph.co.uk/health/healthnews/9824058/Man-flu-does-exist-as-men-suffer-more-from-high-temperatures-when-ill-scientist.html
According to the Daily Fail women are far worse at coping with minor ailments.
http://www.dailymail.co.uk/health/article-2610419/Not-tonight-dear-Ive-got-headache-Women-ARE-likely-sex-pain.html
One minor little head ache and they can't even cope with something as simple as performing the beast with the two backs, while only some of the more extreme forms on death can stop a man performing his matrimonial duties.
So man flu must be a myth, it's in the Fail so it must be true.
First, we blokes are, in fact, typically genetically inferior to the fairer sex because of all those hundreds of genes missing from the Y that remain intact on the X. To demonstrate this, one just needs to examine the proportion of men vs. women affected by genetic diseases such as red/green color blindness or the "royal disease" (the hemophilia B-carrying X chromosome passed on to many European royal houses of the 19th century by Queen Victoria) that afflicted the Tsarevich Alexei and entangled his family with the infamous Rasputin. This is because women, with two X chromosomes, essentially have a backup copy for each gene in case one is defective. Men, lacking backups for almost all of their X chromosome genes, are liable to manifest the illness when their one and only copy of the gene is defective.
That said, this paper really addresses the question of whether the few remaining "normal" genes on the Y (excluding those few dealing directly with sex determination, sperm maturation and so forth that are unique to the Y) are just randomly-chosen lucky survivors of eons of genetic carnage (the canonical "rotting Y" theory) or whether their presence is specifically needed on the Y for some reason.
To test this, the team (made up of scientists at the Whitehead, Univ. of Wash. in St. Louis, and Baylor) sequenced the Y chromosomes of a range of mammals, reasoning that if the remaining functional genes on the Y were just randomly-chosen, different sets of genes would survive on the Y chromosomes of different mammals, each having undergone a unique history of genetic change since the species' last common ancestor eons ago. If however, these genes were actually required on the Y in a range of mammals to significantly enhance male fitness vs. not having them on the Y, then the *same* set of genes should have functionally survived on each of the different mammals' Y chromosomes. This latter result is what the team observed; they also observed that this small set of genes is widely expressed throughout the body, even in tissues that do not obviously differ between males and females.
As yet, the functions of these genes are unknown, but they each have cognate counterparts on the X chromosome. Perhaps each gene's Y version has the same function as its cognate X version. However, since the sequences do differ somewhat, there is the intriguing possibility that the Y and X versions *differ* at least somewhat in their specific functionality. The authors speculate that such differences may lead to functional differences between XX and XY versions of cell types that previously had been assumed to function identically in men and woman, and that this may account for some of the observed differences between men and women in e.g. disease susceptibility and other traits. Thus, although we must suffer our burden as the genetically weaker sex, we may yet have some unique traits to salve our wounded senses of self-worth.
I've also heard it suggested that not having a "backup gene" on the X allows beneficial mutations to occur more easily in men than women, as there's no second alelle counteracting its effect. This normally crops up in discussions of intelligence, since "intelligence-related" disabilities are sex-linked and more prevalent in men, and therefore it seems likely the reverse could be true, if we had a reliable way to measure intelligence.
But even if it is true, that would only mean men display greater variability in intelligence, not that men can be any more intelligence than women. (It would also prevent intelligence passing from the father to the son, which might explain a few things.)
Bit of a fallacious argument implying the genetic intelligence ability is only linked to the X chromosome; Down's Syndrome is normally caused by a single damaged chromosome at position 21 not 23. The degree of this affliction is dependant upon the degree of damage. If two damaged 21s are combined the foetus is normally not viable. Of course you may not agree that Down's Syndrome is "intelligence-related".
The fact that two X chromosomes are available does not mean they have co-effective roles in a tissue's gene expression as the non-used X is coiled as the Bar Body and can't be transcribed by mRNA. Also female expression of the X chromosome is chimeric in that one organ (liver say) may use one X while another organ (lungs) uses the other X, not possible for males.
@Scroticus Canis
I didn't mean to imply intelligence is "only linked to the X chromosome". I apologise for any misphrasing or lack of caveats that led to that conclusion.
See above reply about expression of X chromosomes and a few more caveats. Also Wikipedia on liver cells, "Also, if one X-chromosome has a mutation hindering its growth or rendering it non viable, cells which randomly inactivated that X will have a selective advantage over cells which randomly inactivated the normal allele. Thus...cells that inactivate a normal allele (leaving the mutated allele active) will eventually be overgrown and replaced by functionally normal cells in which nearly all have the same X-chromosome activated."
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