questions about The Selfish Gene

[andyandy]

.....which i've just finished

I've left the title rather vague - as there's a few questions i can think of....but specifically a couple stand out as matters of interest -

1) why are segregation distorters not more common?

brief explanation of segregation distorters here

All nuclear genes in a given diploid genome cooperate because each allele has an equal probability of being present in a gamete. This fairness is guaranteed by meiosis. However, there is one type of gene, called segregation distorter, that "cheats" during meiosis or gametogenesis and thus is present in more than half of the functional gametes. The most studied examples are sd in Drosophila melanogaster (fruit fly), t haplotype in Mus musculus (mouse) and sk in Neurospora sp. (fungus). Segregation distorters that are present in sexual chromosomes (as the X chromosome in several Drosophila species) are denominated sex-ratio distorters, as they induce a sex-ratio bias in the offspring of the carrier individual

I could see how a rise in such distorters could lead to something of an arms race...with rival alleles employing techniques to ensure a greater than 50% chance of selection....but instead nearly all genes are happy with meiosis...why?

2) Dawkins speculates that parasitic viruses spead through sexual contact may in fact increse the libido of those infected - in the same way that dogs catching rabies become inclined to bite those around them....Is there such evidence for that claim today? And, how about the effects of parasites generally on human actions? - We know that say, toxoplasma affects quite dramatically the actions of a rat (making them attracted to cat urine...).
Finally, how is the field of parasite (introduction of parasites for medical benefit) therapy progressing - if at all?

many thanks

 

[Cuddles]

.....which i've just finished

I've left the title rather vague - as there's a few questions i can think of....but specifically a couple stand out as matters of interest -

1) why are segregation distorters not more common?



I could see how a rise in such distorters could lead to something of an arms race...with rival alleles employing techniques to ensure a greater than 50% chance of selection....but instead nearly all genes are happy with meiosis...why?

Off the top of my head, I would say that a mutation that increased the likelyhood of an allele being passed on would be very likely to alter the funcion of the gene in other ways which generally would make it less effective and so be selected against.

I suppose it is entirely possible that this is exaclty what "junk" DNA does. All the junk could actually be genes devoted to ensuring they get passed on, but since they are designed to do this they can't do anything else. Functional genes instead present themselves in the phenotype to increase their survival. A few genes may do both, but this is unusual.

2) Dawkins speculates that parasitic viruses spead through sexual contact may in fact increse the libido of those infected - in the same way that dogs catching rabies become inclined to bite those around them....Is there such evidence for that claim today? And, how about the effects of parasites generally on human actions? - We know that say, toxoplasma affects quite dramatically the actions of a rat (making them attracted to cat urine...).
Finally, how is the field of parasite (introduction of parasites for medical benefit) therapy progressing - if at all?

many thanks

I think parasites affecting human behaviour is extremely likely. If we can see it in other animals why should we be special. I am not aware of any research on this though. I think there would be serious ethical problems here though, since it would open up courts to claims of "the parasites made me do it".

I can't find any research on parasite therapy (not that I looked especially hard), but I find it unlikely that this wil reach humans for a very long time. We have enough problems introducing fairly simple molecules into the human body, so introducing whole organisms without causing serious side-effects will take an awful lot of time to get right.

 

[Nightlord]

1) why are segregation distorters not more common?

I may be wrong, but segregation alleles go against the tendency in nature to have as much variation as possible in a given population, so any allele that forces itself into the next generation can actually lower the adaptability of the population that have it, and for that reason cannot be conserved too long (and the part of the population that have the not-selfish genes would be better adapted to any change in the ecosystem that have anything to do with that gene in particular)

And about parasite therapy there is a lot of work being done about viruses as a vector to deliver genetic therapies, but I don't know if that is what you are asking about

(I apologize in advance for my mistakes, English is not my mother language)

 

[andyandy]

Off the top of my head, I would say that a mutation that increased the likelyhood of an allele being passed on would be very likely to alter the funcion of the gene in other ways which generally would make it less effective and so be selected against.

I suppose it is entirely possible that this is exaclty what "junk" DNA does. All the junk could actually be genes devoted to ensuring they get passed on, but since they are designed to do this they can't do anything else. Functional genes instead present themselves in the phenotype to increase their survival. A few genes may do both, but this is unusual.



I think parasites affecting human behaviour is extremely likely. If we can see it in other animals why should we be special. I am not aware of any research on this though. I think there would be serious ethical problems here though, since it would open up courts to claims of "the parasites made me do it".

I can't find any research on parasite therapy (not that I looked especially hard), but I find it unlikely that this wil reach humans for a very long time. We have enough problems introducing fairly simple molecules into the human body, so introducing whole organisms without causing serious side-effects will take an awful lot of time to get right.

thanks cuddles...i was beginning to think that i'd just posted the least popular thread ever

and welcome to the forum nightlord!

I mentioned the parasite therapy because i remembered vaguely a discovery channel program on parasites in general - and some research was being done on introducing a parasite to the stomach to cure/ease a certain condition. The parasite by accounts, produced some chemicals which seemed to help.....*stupid brain* i can't remember any details.....only that it was in the early stages of research.....
parasites as "medicine" shouldn't be too far fetched though - bottles of liquid containing tape worm eggs used to be sold in the early 20th century as a way of suppressing hunger......

the use of viruses as a delivery system for gene therapy sounds intriguing......any more details?

 

[Cuddles]

As far as I know most gene therapy uses retroviruses to deliver genes. This is because a retrovirus is basically a virus that inserts it's genes into the host's DNA, which then produces more viruses. If an engineered gene is made part of the virus, and the virus is altered to be unable to reproduce, then the engineered gene becomes part of the target's DNA. Unfortunately there is no control over where the gene is inserted, so this is not a very reliable tecnique and has been implicated as a cause of cancer in several trials.

There are other ways of introducing genes, but none of them are as established as retroviral therapy (not that it's particularly established).

http://www.newscientist.com/article/dn5067.html
http://www.newscientist.com/article/mg12517002.200.html
http://www.newscientist.com/article/dn2186.html
http://www.newscientist.com/article/dn2257.html

 

[Angus McPresley]

Finally, how is the field of parasite (introduction of parasites for medical benefit) therapy progressing - if at all?

It's not. All parasite therapy has been shown to cause an unfortunate side effect in patients, the clinical term for which is "the heebs".

 

[Dymanic]

Dawkins speculates that parasitic viruses spead through sexual contact may in fact increse the libido of those infected - in the same way that dogs catching rabies become inclined to bite those around them

He expanded on this sort of idea in a later book, "The Extended Phenotype". One wonders if he may have taken a good idea a bit too far, but it's fascinating stuff nonetheless.

I could see how a rise in such distorters could lead to something of an arms race...with rival alleles employing techniques to ensure a greater than 50% chance of selection....but instead nearly all genes are happy with meiosis...why?

Organisms compete against one another on the macro-battlefields their environments represent -- while simultaneously, another struggle is constantly taking place on the micro-battlefield of the genome. Considering the interplay between the two is an ambitious undertaking; one which seems to grade off into philosopy at some point. Nucleotide sequences (they don't necessarily have to be genes, exactly) which manage, by whatever means, to win for themselves a disproportionate amount of space on a genome, will tend to be represented on subsequent genomes to a disproportionate degree (go figure). If, as a result, the organism hosting the competition becomes less competitive in its own struggles on the macro-battlefield, the greedy sequences may have just stowed away on a sinking ship -- but they can't know that in advance, and genomes have ways of fighting back (one might say, to simplify the matter somewhat). Some biologists believe that "junk DNA" may, to a great extent, represent the relics of battles with (say) retroviruses.

"The Cooperative Gene", by Mark Ridley, is another book that deserves a spot on the reading list of anyone interested in this sort of thing.

 

[andyandy]

Organisms compete against one another on the macro-battlefields their environments represent -- while simultaneously, another struggle is constantly taking place on the micro-battlefield of the genome. Considering the interplay between the two is an ambitious undertaking; one which seems to grade off into philosopy at some point. Nucleotide sequences (they don't necessarily have to be genes, exactly) which manage, by whatever means, to win for themselves a disproportionate amount of space on a genome, will tend to be represented on subsequent genomes to a disproportionate degree (go figure). If, as a result, the organism hosting the competition becomes less competitive in its own struggles on the macro-battlefield, the greedy sequences may have just stowed away on a sinking ship -- but they can't know that in advance, and genomes have ways of fighting back (one might say, to simplify the matter somewhat). Some biologists believe that "junk DNA" may, to a great extent, represent the relics of battles with (say) retroviruses.

"The Cooperative Gene", by Mark Ridley, is another book that deserves a spot on the reading list of anyone interested in this sort of thing.

ok....i can certainly understand that if such an action was detrimental to the host organism, then in the long term it would be a poor policy to affect meiosis,

but,

for say a gene (or nucleotide sequence) for something benign like hair colour/eye colour i don't see why such an action would be detrimental to the long term survival of the species....
as a "selfish" gene would i not be better off employing some sort of segregation distortion? Even if i tip the balance to 51/49 %, then i'm ensuring a greater chance of long term success....and at no longer term detriment (that i can see...) to my vehicle....
and yet, genes "accept" the meiosis lottery.....

 

[Cuddles]

ok....i can certainly understand that if such an action was detrimental to the host organism, then in the long term it would be a poor policy to affect meiosis,

but,

for say a gene (or nucleotide sequence) for something benign like hair colour/eye colour i don't see why such an action would be detrimental to the long term survival of the species....
as a "selfish" gene would i not be better off employing some sort of segregation distortion? Even if i tip the balance to 51/49 %, then i'm ensuring a greater chance of long term success....and at no longer term detriment (that i can see...) to my vehicle....
and yet, genes "accept" the meiosis lottery.....

The problem is that no gene we have found so far only affects one thing. A gene for blue eyes might also affect skin pigment, so any change could have bad effects. The idea of a gene for blue eyes is what Terry Pratchett would call "lies to children". It is a nice idea and useful for explaining the basic concept of genes, but is not the actual truth when looked at more closely.

Since very few genes do employ segregation distortion the obvious conclusion is that there is something preventing this.

Edit : Or that we just haven't noticed them doing it of course.

 

[Nightlord]

ok....i can certainly understand that if such an action was detrimental to the host organism, then in the long term it would be a poor policy to affect meiosis

The problem is that there is no way to know what will be detrimental to the organism because there are countless possibilities. So, even if a certain characteristic seems not so important to the host survival right now (and even in the hypothetical case that one thing is controlled by only a gene and that gene controls only that), there is no way to know if that is going to be that way forever, any change in the environment can put in disadvantage to the population that have that selfish gene (even if its only because the members of that species prefer to mate with individuals with a specific hair or eye color). So in the long way anything can be important.

And also, in genetics most of the time the balance is quite fragile, if there is two options and one is expressed or transmitted to the next generation easier than the other, normally that other option tends to disappear in just a few generations, even a small advantage in the genetic level gets bigger and bigger on each generation until it get into a balance with the disadvantages on the species level.

 

[andyandy]

The problem is that no gene we have found so far only affects one thing. A gene for blue eyes might also affect skin pigment, so any change could have bad effects. The idea of a gene for blue eyes is what Terry Pratchett would call "lies to children". It is a nice idea and useful for explaining the basic concept of genes, but is not the actual truth when looked at more closely.

Since very few genes do employ segregation distortion the obvious conclusion is that there is something preventing this.

Edit : Or that we just haven't noticed them doing it of course.

sure, talking about a "gene" for eye colour is a gross simplication, but it's one which dawkins uses throughout the selfish gene (where "gene" can be a unit of genes....) - he frames most of his arguments for the selfish gene theory in this language....

therefore it would be pertinent to ask why the same logic doesn't extend to meiosis...

i'm sure i must be missing something

EDIT
Just reading nightlord's post.....
I can see the logic - like cuddles, you're suggesting that gene changes to meiosis could be detrimental to future generations....
but i'm not sure why meiosis would remain stable at 50% 50%....wouldn't genes constantly be testing those boundaries - say to 51% 49% - or 50.01% to 49.99% whatever, because one genes advantage over another doesn't necessarily have to be detrimental to a species...so you'd expect them to benefit from experimentation....

 

[Dymanic]

as a "selfish" gene would i not be better off employing some sort of segregation distortion?

If you don't contribute to overall fitness, it's about all you've got. And thwarting you is in the best interest of all the other genes. If you're an outright detriment to fitness, thwarting guys like you is important enough to all the other genes to make the meiosis lottery a worthwhile gamble for them.

 

[Roboramma]

2) Dawkins speculates that parasitic viruses spead through sexual contact may in fact increse the libido of those infected - in the same way that dogs catching rabies become inclined to bite those around them....Is there such evidence for that claim today? And, how about the effects of parasites generally on human actions? - We know that say, toxoplasma affects quite dramatically the actions of a rat (making them attracted to cat urine...).
Finally, how is the field of parasite (introduction of parasites for medical benefit) therapy progressing - if at all?

Well, regarding toxoplasma anyway, I just read something interesting in Parasite Rex (by Carl Zimmer) yesterday. Here's a little excerpt:

By turning rats into rodent kamikazes, Toxoplasma probably increases its chances of getting into cats. If it makes the mistake of getting into a human instead of a rat, it has little hope of making that journey, but there's some evidence that it still tries to manipulate its host. Psychologists have found that toxoplasma changes the personality of its human hosts, bringing different shifts to men and woman. Men become less willing to submit to the moral standards of a community, less worried about being punished for breaking society's rules, more distrustful of other people. Women become more outgoing and warmhearted. Both changes seem to break down the fear that might keep a host out of danger. They're hardly enough to make people throw themselves at lions, but they're a very personal reminder of the ways in which parasites try to take control of their destiny.

 

[trvlr2]

Off the top of my head, I would say that a mutation that increased the likelyhood of an allele being passed on would be very likely to alter the funcion of the gene in other ways which generally would make it less effective and so be selected against.

I suppose it is entirely possible that this is exaclty what "junk" DNA does. All the junk could actually be genes devoted to ensuring they get passed on, but since they are designed to do this they can't do anything else. Functional genes instead present themselves in the phenotype to increase their survival. A few genes may do both, but this is unusual.



I think parasites affecting human behaviour is extremely likely. If we can see it in other animals why should we be special. I am not aware of any research on this though. I think there would be serious ethical problems here though, since it would open up courts to claims of "the parasites made me do it".

I can't find any research on parasite therapy (not that I looked especially hard), but I find it unlikely that this wil reach humans for a very long time. We have enough problems introducing fairly simple molecules into the human body, so introducing whole organisms without causing serious side-effects will take an awful lot of time to get right.

http://www.zoo.ufl.edu/bolker/eep/notes/week5.html

http://www.cdc.gov/ncidod/EID/vol8no9/02-0204.htm

Above are interesting links to behavior modifying parasites.
Indeed, it seems that all is not what it seems on the surface. Humans may be manipulated by parasites as well as other animals.
But first one must imagine that the behavior is somehow "wrong", to begin to look for the parasitic organism. "Wrong" meaning that the behavior is not to the benefit of the host. Some wrong behavior may be very subtle,and not actually kill the host.
Do you suppose that our diseases are caused by parasitic organisms not quite sophisticated enough , yet, to not kill? And that, maybe, the really sophisticated parasites only modify (us) just enough to ensure their survival?
Perhaps the junk dna IS part of former/ongoing attacks on our true selves?
Perhaps we owe some of what we really are to these attackers.
A thought I have had recently(very entertaining,to me), is that there is a religion virus, not just a cultural meme, but an actual virus,which seems to infect 2/3 of the human population. Why else would the church want to get kids under 7 years (undeveloped immune system)?And why do our modern religions have their root in the very place where we suspect humans originated?(host& parasite co-evolving. Pun intended.) Mentioning in aside-that religious ecstasy is/can be related to epileptic conditions-virii cross the blood/brain barrier easily.Maybe other mental illness can be related to a viral infection? Maybe this is why people "get religion" like the chicken pox, and some "get over it"? Perhaps an immunological study could find a link between the relative activity of the immune system before and after "getting religion.
As I said, pure speculation,but I find it entertaining. Me& my colonies of critters gotta go-G'day.

 

[Dave1001]

2) Dawkins speculates that parasitic viruses spead through sexual contact may in fact increse the libido of those infected - in the same way that dogs catching rabies become inclined to bite those around them....Is there such evidence for that claim today?

Good question, and it should be pretty easy to design experiments & studies to test for this.

 

[andyandy]

Good question, and it should be pretty easy to design experiments & studies to test for this.

hmmm....testing it for humans could be interesting.....how would you suggest doing so?

 

[Roboramma]

By the way, as regards parasite medicine, I read something interesting in Parasite Rex this morning:

In 1997, scientists at the University of Iowa put this idea into startling practice. They picked out seven people with ulcerative colitis and Crohn's disease, who had gotten no relief from any conventional treatment. They fed them eggs from an intestinal worm that normally lives in an animal, one that wouldn't cause any disease of its own in the human gut (the scientists are still keeping the species a secret until they've finished their research). Within a couple of weeks the eggs had hatched, and the larvae had grown, and six ut of the seven people went into complete remission.

Of course it's a tiny study with a horribly small sample size. I don't know if more studies were done subsequently, or what happened with that research, but it shows that there are at least some people still thinking about the idea, and that it may have some limited uses, even now. It'd be interesting if it ever comes into widespread use.
Very cool in my opinion.

 

[andyandy]

By the way, as regards parasite medicine, I read something interesting in Parasite Rex this morning:



Of course it's a tiny study with a horribly small sample size. I don't know if more studies were done subsequently, or what happened with that research, but it shows that there are at least some people still thinking about the idea, and that it may have some limited uses, even now. It'd be interesting if it ever comes into widespread use.
Very cool in my opinion.

cheers robo

that sounds pretty similar to what i saw on the discovery channel program.....

it's a fascinating idea....