How long before this is turned on certain groups of people?
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Exterminate, exterminate
Mar 20th 2003
From The Economist print edition
Genetically engineered extinction
MANKIND has exterminated many species carelessly, but only one deliberately. Smallpox viruses were eliminated in the wild in the 1970s, though they remain in two known (and probably several unknown) laboratories around the world. In general, the sorts of species that people want to get rid of?pests, parasites and pathogens?resist extermination. But Austin Burt, a geneticist at Imperial College, London, may have found a way to deal with them. In a paper just published in the Proceedings of the Royal Society, he describes how to spread genes that will lead to the extinction of almost any sexually reproducing species.
Genes, as Richard Dawkins observed, are selfish. But some are more selfish than others. So-called site-specific selfish genes (SSSGs) are particularly solipsistic. Not content with reproducing along with the cells containing them, they also transfer themselves from one chromosome to another within a cell. That means they can rapidly become ubiquitous.
They perform this trick by exploiting their hosts' cellular machinery to insert themselves into the DNA of new chromosomes. Normally, this does no damage. Most DNA does not actually carry genetic information, and if an SSSG lands in such a piece of junk it will do little harm. Dr Burt's suggestion is to alter the site an SSSG prefers, so that it inserts itself into the middle of something that does matter, such as a gene. Thus disrupted, the target gene would no longer work.
The SSSGs that Dr Burt has his eye on are a group called homing endonuclease genes (HEGs). When one of these gets into a chromosome, it causes the production of an enzyme called endonuclease. This acts as a pair of molecular scissors, cutting DNA molecules at any place that has a specific sequence of the nucleotide ?letters? of which DNA is composed.
Cells have two copies of most chromosomes (one deriving from the mother, and one from the father). If only one of these carries an HEG, the other will be cut by the enzyme which that gene produces. The site of the cut corresponds to the site of the HEG on the ?infected? chromosome. The infected chromosome itself is not cut, because the HEG is in the middle of the enzyme-recognised sequence, and thus disguises it. But, since cells repair chromosomal damage by replacing the corrupted DNA with a copy from the same place on the partner chromosome, the HEG is copied over as part of the repair process.
Now, instead of one copy of the broken gene, the cell has two. And if this happens while eggs or sperm are being produced, then all the eggs or sperm will have the HEG-disrupted gene, even though the parent had only one copy. And so it comes to pass, in computer simulations at least, that HEG-disrupted genes propagate madly through any population into which they are introduced.
To cause extinction, the secret is to pick a target gene that results in few problems if only one copy per cell is disrupted, but causes death if both copies are disrupted. In this case, the disrupted version spreads, according to the models, until it is so common that 80% of embryos die before they mature. Use several HEGs, with different genetic targets, and that percentage can be forced well above 95%. At this point, too few offspring are produced to replace the parents, so the species gradually dwindles to extinction.
The question is how to get an HEG to change its mind about which piece of DNA its enzyme should cut, so that it ends up in the middle of a gene. That will not be easy, but modern ?molecular breeding? techniques, with which genetic engineers shuffle genetic material and then select from the results for particular features, as an animal breeder selects for, say, coat colour, may do the trick. After that, it will be a question of deciding which species to try to get rid of, designing suitable HEGs, putting them into a few individuals and releasing those individuals into the wild. Disease-carrying mosquitoes are likely to be high on the list. But if your neighbour is a genetic engineer, perhaps you shouldn't let the dog bark too loudly late at night.
link
Exterminate, exterminate
Mar 20th 2003
From The Economist print edition
Genetically engineered extinction
MANKIND has exterminated many species carelessly, but only one deliberately. Smallpox viruses were eliminated in the wild in the 1970s, though they remain in two known (and probably several unknown) laboratories around the world. In general, the sorts of species that people want to get rid of?pests, parasites and pathogens?resist extermination. But Austin Burt, a geneticist at Imperial College, London, may have found a way to deal with them. In a paper just published in the Proceedings of the Royal Society, he describes how to spread genes that will lead to the extinction of almost any sexually reproducing species.
Genes, as Richard Dawkins observed, are selfish. But some are more selfish than others. So-called site-specific selfish genes (SSSGs) are particularly solipsistic. Not content with reproducing along with the cells containing them, they also transfer themselves from one chromosome to another within a cell. That means they can rapidly become ubiquitous.
They perform this trick by exploiting their hosts' cellular machinery to insert themselves into the DNA of new chromosomes. Normally, this does no damage. Most DNA does not actually carry genetic information, and if an SSSG lands in such a piece of junk it will do little harm. Dr Burt's suggestion is to alter the site an SSSG prefers, so that it inserts itself into the middle of something that does matter, such as a gene. Thus disrupted, the target gene would no longer work.
The SSSGs that Dr Burt has his eye on are a group called homing endonuclease genes (HEGs). When one of these gets into a chromosome, it causes the production of an enzyme called endonuclease. This acts as a pair of molecular scissors, cutting DNA molecules at any place that has a specific sequence of the nucleotide ?letters? of which DNA is composed.
Cells have two copies of most chromosomes (one deriving from the mother, and one from the father). If only one of these carries an HEG, the other will be cut by the enzyme which that gene produces. The site of the cut corresponds to the site of the HEG on the ?infected? chromosome. The infected chromosome itself is not cut, because the HEG is in the middle of the enzyme-recognised sequence, and thus disguises it. But, since cells repair chromosomal damage by replacing the corrupted DNA with a copy from the same place on the partner chromosome, the HEG is copied over as part of the repair process.
Now, instead of one copy of the broken gene, the cell has two. And if this happens while eggs or sperm are being produced, then all the eggs or sperm will have the HEG-disrupted gene, even though the parent had only one copy. And so it comes to pass, in computer simulations at least, that HEG-disrupted genes propagate madly through any population into which they are introduced.
To cause extinction, the secret is to pick a target gene that results in few problems if only one copy per cell is disrupted, but causes death if both copies are disrupted. In this case, the disrupted version spreads, according to the models, until it is so common that 80% of embryos die before they mature. Use several HEGs, with different genetic targets, and that percentage can be forced well above 95%. At this point, too few offspring are produced to replace the parents, so the species gradually dwindles to extinction.
The question is how to get an HEG to change its mind about which piece of DNA its enzyme should cut, so that it ends up in the middle of a gene. That will not be easy, but modern ?molecular breeding? techniques, with which genetic engineers shuffle genetic material and then select from the results for particular features, as an animal breeder selects for, say, coat colour, may do the trick. After that, it will be a question of deciding which species to try to get rid of, designing suitable HEGs, putting them into a few individuals and releasing those individuals into the wild. Disease-carrying mosquitoes are likely to be high on the list. But if your neighbour is a genetic engineer, perhaps you shouldn't let the dog bark too loudly late at night.
