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I found a paper on genetical modification of mosquitos disrupting malaria. There is an intresting excerpt conserning proliferation of a desired gene into whole population:

All gametes arising from such an event will pass on the [Cas9-gRNA] cassette to their progeny, just as with naturally occurring HEGs (Figure 1B). In both mosquito studies, the crossing of a heterozygous MCR-carrier to a wild-type individual resulted in transmission of the allele to over 90% of the progeny, demonstrating strong genetic drive compared to the 50% inheritance predicted by Mendelian genetics.

It made me wonder if that is a one-of-a-kind situation or it is possible to change the whole population of any species by introduction of a few modified specimens and then just wait. Some ideas if it is possible:

  1. A nefarious scientist inserts the morphine gene from poppy into a common garden weed, disperses several kilos of seeds from his biplane, then cackles of drug epidemics 5 years later.
  2. The fact that all suspects have large families catches the eye of a detective. It turns out that they are members of a secret eugenics society that wants to disseminate certain beneficial genes despite harsh ban on human modification.
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The general term for the technique described in the paper is gene drive. It has been suggested as a way of controlling or even eradicating insects that spread diseases, but no large scale attempts have yet been made.

In principle gene drive could be used to spread a modification in any population, but if you try it on a species like humans, who generally begin to reproduce in their late teens at the earliest and can live up to 100 years, you have to wait quite long for the construct to spread through a significant part of the population. How many generations it takes depends on how many modified individuals are present at the beginning.

Also, the modification can't be very harmful, or it will not spread efficiently. Moderate harmfulness isn't enough to stop it though; that Wikipedia article linked above even says (based on a reference) the gene drive can cause up to a 30% reduction in reproduction success and is still likely to eventually spread through the whole population.

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Natural Selection

If the modification is useful and hereditary the process by which is proliferates among the whole population is called natural selection.

Modified individuals are more likely to live longer and breed more. So generation 2 has more modified individuals than unmodified ones. Over time the whole population becomes modified.

However your excerpt does not suggest the modification in the paper is beneficial. It only says it passes to the offspring 90% of the time.

Your scientist needs to make his modified dandelion produce opiates and also be stronger and grow faster than normal weeds. These super weeds will kill all the other weeds in the garden.

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  • $\begingroup$ No, this is true in the normal situation, but in the artificial case of gene drive it doesn't have to be stronger or faster, it needs to be not significantly weaker. ¶ E.g. in a stable population, if you have a mutant Z gene, on the average you will have 2 children that survive and 1 of them will inherit that gene. The percentage of Z within the population gene pool remains unchanged. If you have a mutant Z gene with a "90% gene drive" modification, you will have 2 children that survive, and 1.8 of them will inherit that gene. The percentage of Z within the general population will increase. $\endgroup$ Jun 19 at 1:19
  • $\begingroup$ @RayButterworth Yes you are right. Beneficial mutations only have 50% inheritance on average. It the drive is larger than that it doesn't need to be beneficial. $\endgroup$
    – Daron
    Jun 19 at 9:06

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