It only causes female sterility, so the males keep passing it on. It reaches the whole population because the gene encodes a protein that affects the DNA and ensures it’s inheritance, rather than being a fifty fifty. If a modified and unmodified mate, then their offspring have only one copy of the modified DNA and one copy of the unmodified. They would have only a fifty fifty chance of passing that on. But if the gene has the effect of breaking other (nonmodified) copy, then the organisms natural DNA repair mechanisms will copy from the other chromosome to repair the damage. That copies the modified gene over! Now it has only the modified DNA and will pass it on with 100% chance. So will it’s offspring, forever, until there are no nonsterile females.
Gene drives (I.e. genes that force their own propagation) do arise in nature. There are “LINE” genes that apparently make up over 20% of our genome: they encode RNA that encodes a protein that takes its own RNA and copies it back into your DNA at random locations, thereby propagating itself even more than our engineered gene drives do. With it taking up that much of our genome, I could imagine something like that killing off a species, though I’m failing to find a specific example.These are examples of selfish genes, so that might be where to read more.
Here is an example of something that comes close from “The Selfish Gene”:
One of the best-known segregation distorters is the so-called t gene in mice. When a mouse has two t genes it either dies young or is sterile, t is therefore said to be lethal in the homozygous state. If a male mouse has only one t gene it will be a normal, healthy mouse except in one remarkable respect. If you examine such a male’s sperms you will find that up to 95 per cent of them contain the t gene, only 5 per cent the normal allele. This is obviously a gross distortion of the 50 per cent ratio that we expect. Whenever, in a wild population, a t allele happens to arise by mutation, it immediately spreads like a brushfire. How could it not, when it has such a huge unfair advantage in the meiotic lottery? It spreads so fast that, pretty soon, large numbers of individuals in the population inherit the t gene in double dose (that is, from both their parents). These individuals die or are sterile, and before long the whole local population is likely to be driven extinct. There is some evidence that wild populations of mice have, in the past, gone extinct through epidemics of t genes.
Not all segregation distorters have such destructive side-effects as t. Nevertheless, most of them have at least some adverse consequences.
From the discussion of human-engineered gene drives, they would only cause sterility in one sex, which would help avoid the gene dying off as quickly.
Is there an easy to understand explanation about why a sterility causing gene drive will spread through the population?
It only causes female sterility, so the males keep passing it on. It reaches the whole population because the gene encodes a protein that affects the DNA and ensures it’s inheritance, rather than being a fifty fifty. If a modified and unmodified mate, then their offspring have only one copy of the modified DNA and one copy of the unmodified. They would have only a fifty fifty chance of passing that on. But if the gene has the effect of breaking other (nonmodified) copy, then the organisms natural DNA repair mechanisms will copy from the other chromosome to repair the damage. That copies the modified gene over! Now it has only the modified DNA and will pass it on with 100% chance. So will it’s offspring, forever, until there are no nonsterile females.
Could such a gene arise spontaneously in nature and be the final reason for the elimination of a species?
Gene drives (I.e. genes that force their own propagation) do arise in nature. There are “LINE” genes that apparently make up over 20% of our genome: they encode RNA that encodes a protein that takes its own RNA and copies it back into your DNA at random locations, thereby propagating itself even more than our engineered gene drives do. With it taking up that much of our genome, I could imagine something like that killing off a species, though I’m failing to find a specific example.These are examples of selfish genes, so that might be where to read more.
Here is an example of something that comes close from “The Selfish Gene”:
From the discussion of human-engineered gene drives, they would only cause sterility in one sex, which would help avoid the gene dying off as quickly.
Yes, definitely. Although we don’t have any examples of this happening, since those species would have gone extinct, making them unable to be studied.