Chlorine for the gene pool?

From an evolutionary perspective, diversity in the gene pool increases the chances that a species will survive. In humans, most variations aren't going to have much impact on our survival, such as eye color, or whether sunlight gives us freckles.However, there are some genes that cause diseases and disorders, such as an inclination towards cancer. Most people would label these genes as "bad," because they lower the quality of life, or end it all together. It would make sense that removing these genes from our gene pool would then be a "good" thing.There is only one problem. Wouldn't that reduce the variation in our gene pool? If we were to accomplish the removal of these "bad" genes, could the reduction in diversity ultimately be harmful to the survival of our species?I would like this discussion to focus solely on the medical and evolutionary aspects.I would not like this discussion to focus on the social aspects or the specific mechanism by which we might accomplish the removal of disease causing genes.Suggested forum: Biological evolution

Thread moved here from the Proposed New Topics forum.

Not really. You can't reduce the 'overall' variation in the gene pool without putting the entire population through some kind of severe bottleneck event. What you are talking about is the 'selective' removal of particular genes that reduce longevity or quality of life. Were it possible to accomplish this, it would be a good thing, although not a permanent solution. Most of those deleterious genes were produced by mutations in functional genes that probably continue to occur with some frequency, thus more of them will eventually arise purely by chance. No, because any appreciable reduction in overall genetic diversity in the human population could only be brought about by a very dramatic population reduction. Genetic diversity can only be limiting to a species' survival when its effective population size is very small. Edited by EZscience, : seplling

I had to promote it straight away EZScience has covered this quite well. The first complication is pleiotropy. Some (maybe most I don't know) genes have multiple effects and it may not be possible to extract certain 'bad' genes. As you say though, this is by the by. If it were possible then what.Then we come to the other issue. What is bad today, might be good tomorrow. Turning pure speculation mode on, it might be possible that cancer/some other disease could be beneficial to the species later on. With cancer it might be that a further mutation to the 'cancer gene' could provide the next step in evolution.So - it might be ultimately harmful to remove cancer genes, or it might ultimately beneficial...who can say?

Were it possible, new harmful variations could be removed, as well. With the proper technology, we wouldn't have to limit population. Something akin to what was done in the movie Gattaca could do this without having to cull our own herd. But like I said, I would rather not get into the social or technological specifics.

This was one thing I was thinking of. Another complication might be the effects of combinations of genes. I would imagine certain genetic diseases might arise out of specific combinations of genes.A simple example might be Sickle Cell Anemia. IIRC, Sickle Cell Anemia comes about when a person has two copies of a certain gene. A person with only one copy of that gene has a better resistance to Malaria, though.

Precisely so. The 'adaptive value' of an allele, be it positive or negative, is determined by the environment in which it occurs. We can define this 'environment' as either the genotype of the indivdual in which the allele is expressed (variable pleotropic effects are possible within this context) or the phsyical environment within which the organism resides.For example, consider this reference I just came across:Variation in fecundity and sexual morph production among insecticide-resistant clones of the aphid Schizaphis graminum (Homoptera: Aphididae).Rider,-S-D,-Jr; Wilde,-G-E
Journal-of-Economic-Entomology. 1998; 91(2): 388-391

quote:

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This study further substantiates that fecundity is variable, and suggests that insecticide resistance may be associated with reduced fecundity in certain insecticide-resistant clones.

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This is not uncommon. A gene for insecticide resistance often exacts a 'cost' relative to alternative alleles in the absence of the strong selective force (the insecticide), making it a 'bad' gene to carry under normal conditions.But it's not a 'bad' to carry if you have to live in a wheat field owned by a nozzle-head farmer who hoses you down with insecticide every couple of weeks...

Not to split hairs, but the problem at that point would be one of detection. Assuming the technology to selectively correct known deleterious mutations carried by specific individuals in their germ cell lines, how would you know who to check for the ones produced by novel mutation events? It would be easy to identify and 'cure' those expressing the deleterious genes, but when the mutation occurred 'de novo' in a single egg or sperm, how would you know? The parent would be symptomless.

It would take some number of generations before we could identify a new harmful mutation.

That would depend on just how deleterious the mutation is and its mode of inheritance.
If it were extremely deleterious and dominant, we might not even be aware it had happened because no fetus would be brought to term.
At the next level of dominant inheritance, we might have successful live birth of severely disadvantaged offspring easily recognizable as such in the F1 generation.
In the case of incomplete dominance, heterozygotes would be intermediately disadvantaged relative to homzygotes in the F1.
In the case of a fully recessive allele, we would only see 1/4 of offspring affected in the F2 generation (assuming simple Mendelian inheritance). And you would never recognize the heterozygote carriers of this recessive mutant without genetic tests specifically targeting this locus.And that is still the simplest of possible scenarios without considering pheneomena such as pleotropy, epistasis or selective penetrance...Edited by EZscience, : No reason given.Edited by EZscience, : No reason given.

I'm not entirely sure what that means. Is it something to the effect of how many offspring a specific aphid can produce?If so, I don't think such a trait would apply, because I don't think such variation would be considered a disease. I'm not talking about specifically targeting the variation found in one trait (i.e. fecundity). I'm talking about targeting specific diseases that have specific genetic causes, such as hemophilia.Keep in mind, I'm not a biologist, so if hemophilia is a bad example, a disease that would serve as a better example would be appreciated.

I think the point was commenting on pleiotropy and how the environment determines what is good and what is bad.If the aphids live in an area with no humans then a gene that reduces their fecundity would be considered bad. This would be a congenital disease. If aphids had language they might call it "Dondo's syndrome" or something, a disease which renders the person unable to create a normal amount of children. This doesn't have an effect on the parent but it does have an effect on the survival prospects of the genes in the parent. I suspect you were looking for a more obvious disease, but this works in the same way. If she had a disease that reduced her reproductive lifespan (ie she died after only giving birth to half the normal kids), it would have the same effect genetically speaking.Unless, of course, you want to discuss diseases that come on soley in old age after reproduction is possible, but I doubt that.The fecundity harming gene above is 'bad' in a human free population, but if that same gene also provided you with resistance to insecticides, you might do quite better in a human farmed area, than your vulnerable but virile counterparts.That is to say: What is considered a disease in one environment, might not be referred to as a disease in another. Indeed, resistant aphids might say their unresistant cousins had the congenital disease of "Valentine's curse" - they have offspring twice as frequently (actually, I didn't read the paper in detail so I'm taking liberties here), but they die four times as fast.Edited by Modulous, : aphids have odd sexualities, so removed references to 'mother' in case I got it wrong!

I know you're thinking about diseases, but the point is that so many genes can be positive or negative in effect on fitness DEPENDING on what genotype they occur in, or what habitat they occur in.If you want a disease example of this, the textbook one is scile cell anemia. With only one copy of the faulty gene, your resistance to malaria is increased. With two copies, your fitness is severely reduced. This is one of the few proven examples of 'overdominance' - heterozypotes being more fit than either homozygote. But that only holds in environments where malaria is a significant force on the population.For haemophilia, it is more black and white. There is no known benefit for heterozygotes and homozygotes are severely disadvantaged, so if you could detect and remove/correct the mutation in the zygote it would almost certainly be beneficial.
Your problem would come with detecting novel mutations TO that particular allele becuase you wouldn't know where to look for them.ABE: Forgot to answer question. 'Fecundity' is the number of offspring you produce in your lifetime.Edited by EZscience, : No reason given.

For face value, removing those potentially fatal flaws within the code might seem like a very good thing. I mean, theoretically, it makes perfect sense. And perhaps it would give us some immediate gratification and put our minds at ease. By 'immediate' maybe that means 100 years. Who really knows? You also made a very good point that diversity is very important to any species. But the underlying factor IMO is that eugenics has serious sociological implications attached to it. I'm not sure if any of you have seen the movies 'Gattica' or 'The Island,' but they present a logic reason why eugenics is not a good thing. Imagine some people being classed as 'pure' and 'disease-fee.' What should happen to the poor and disenfranchised members of society who have not had their genome tampered with in utero, or what have you? It would be the next form of racism or sexism or agism. There would be this stigma associated with those underprivalged people. Aside from which, no one really knows if there would be long term affects to this act of 'playing God.'For these reasons, I say, let the chips fall where they may and stop trying to usurp Nature/God. As a theist, this goes without saying. But even an evolutionist, I think, could appreciate that supplanting natural selection and replacing it with human selection could have dire consequences for the entire species.What do you think?I would like this discussion to focus solely on the medical and evolutionary aspects.I would not like this discussion to focus on the social aspects or the specific mechanism by which we might accomplish the removal of disease causing genes.

This topic is specifically not addressing the social ramifications, so the bulk of your post about 'serious sociological implications' is off topic.You finish by asking the same question, in different terms, as the OP does. That is 'it might seem to be a good idea, but is it really?'And then you pasted the part in the OP that said it wanted to discuss the medical/evolutionary aspects (and not the social ones). And hence my confusion.If you'd like to discuss the specific evolutionary consequences of ridding the world of genetic diseases then please pull up a stool. If you want to go into sociological territory, then please propose a new topic about it.Comments to be posted in the appropriate thread in my sig (ie don't reply to this post in this thread).

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