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If the gene makes individuals less viable, the distant cousin without the gene is going to outcompete carriers of the gene. Unless we come up with a way to inje

by nikanj 9y ago

If the gene makes individuals less viable, the distant cousin without the gene is going to outcompete carriers of the gene. Unless we come up with a way to inject a gene into all individuals in a biome simultaneusly, but in that case all offspring are going to have the gene, drive or no drive. If the gene makes offspring more viable, how will it wipe out anything, except maybe the individuals without the gene?

klodolph 9y ago
That's not how evolution works. Evolution does not select individuals, it selects genes. Let's say that one of these genes kills offspring with probability 25%, but has gene drive so it's present in 100% of offspring. A normal gene doesn't kill offspring, but is only present in 50% of the offspring. The introduced gene will spread rapidly, since it has a 100% x 75% = 75% chance of being in a living offspring, even though it kills, since the ordinary gene only has a 50% x 100% = 50% chance of being in a living offspring. That's why this is so terrifying. You can introduce a gene into a population that kills off the whole population. https://en.wikipedia.org/wiki/Gene_drive https://en.wikipedia.org/wiki/Gene_drive
- littlestymaar 9y ago
  Actually is the gene is too efficient at killing its offspring, it will kill its bearers before it can spread, and if it's not lethal enough, the population will just deal with it. At 25%, it should allow the gene to spread in the population, but whether it's enough to eradicate the population depends on a lot of thing (the environment, how old the individuals die, etc.)
  - AlanSE 9y ago
    natural factors already causes a fairly high mortality of offspring before they get to reproductive age, and it seems like very few species would be able to cope with an additional 3-of-4 culling for an indefinite period of time.
Obi_Juan_Kenobi 9y ago
You're missing a very critical detail. Normally, for a trait to grow in a population, you need a fitness advantage. Basically, if you average a little over 2 offspring that successfully breed, that trait should grow to fixation. In the case of exactly 2 reproducing offspring, allele count is static. Homozygous parents will provide one allele to each offspring, so 2 copies in one generation, and 2 copies in the next. Heterzygotes have a 50% chance, so one offspring is expected to have the allele. 1 copy in the parent generation, 1 copy in the next. Gene drive changes the completely, as the construct will copy itself to the homologous chromosome. You'll go from 2 to 4 or 1 to 2 copies from the previous example. The growth is exponential. There is nothing like that in nature. Thus, even if a moderate fitness disadvantage is introduced, the allele can still be driven to fixation quite easily. Even with an expected offspring of 1.5, you can still go from 1 to 1.5 copies of the allele over each generation. The other issue is that you can introduce a trait for e.g. chemical susceptibility. It offers no fitness disadvantage until that chemical is introduced into the environment.

by nikanj 9y ago

klodolph 9y ago

That's not how evolution works. Evolution does not select individuals, it selects genes. Let's say that one of these genes kills offspring with probability 25%, but has gene drive so it's present in 100% of offspring. A normal gene doesn't kill offspring, but is only present in 50% of the offspring. The introduced gene will spread rapidly, since it has a 100% x 75% = 75% chance of being in a living offspring, even though it kills, since the ordinary gene only has a 50% x 100% = 50% chance of being in a living offspring. That's why this is so terrifying. You can introduce a gene into a population that kills off the whole population. https://en.wikipedia.org/wiki/Gene_drive https://en.wikipedia.org/wiki/Gene_drive

littlestymaar 9y ago
Actually is the gene is too efficient at killing its offspring, it will kill its bearers before it can spread, and if it's not lethal enough, the population will just deal with it. At 25%, it should allow the gene to spread in the population, but whether it's enough to eradicate the population depends on a lot of thing (the environment, how old the individuals die, etc.)
- AlanSE 9y ago
  natural factors already causes a fairly high mortality of offspring before they get to reproductive age, and it seems like very few species would be able to cope with an additional 3-of-4 culling for an indefinite period of time.

Obi_Juan_Kenobi 9y ago

You're missing a very critical detail. Normally, for a trait to grow in a population, you need a fitness advantage. Basically, if you average a little over 2 offspring that successfully breed, that trait should grow to fixation. In the case of exactly 2 reproducing offspring, allele count is static. Homozygous parents will provide one allele to each offspring, so 2 copies in one generation, and 2 copies in the next. Heterzygotes have a 50% chance, so one offspring is expected to have the allele. 1 copy in the parent generation, 1 copy in the next. Gene drive changes the completely, as the construct will copy itself to the homologous chromosome. You'll go from 2 to 4 or 1 to 2 copies from the previous example. The growth is exponential. There is nothing like that in nature. Thus, even if a moderate fitness disadvantage is introduced, the allele can still be driven to fixation quite easily. Even with an expected offspring of 1.5, you can still go from 1 to 1.5 copies of the allele over each generation. The other issue is that you can introduce a trait for e.g. chemical susceptibility. It offers no fitness disadvantage until that chemical is introduced into the environment.