There are lots of examples of unexpected selective outcomes.
A story—a long time agon a swedish researcher tried to increase wheat yields by picking the biggest wheat kernels to plant. In only 5 generations he had a strain of wheat that produced 6 giant wheat kernels per stalk.
When scale insects were damaging citrus fruits, farmers tried to poison them with cyanide. They’d put a giant tent over the whole tree and pump in the cyanide and kill the scale insects. Plants can be immune to cyanide but no animal that depends on respiration can be. And yet in only 5 years or so they got resistant scale insects. The resistant insects would—when anything startling happen—sit very still and hold their breath for half an hour or so.
If you want to do directed evolution, you do better to do it in controlled conditions. Take your results and test them carefully and make sure they’re what you want before you release them. Microbiologists who want mutants for research commonly take 20 or 100 mutants who survive the conditions they’re selected to survive, and test until they get a few that appear to be just what they want. Eliminate the rest.
So, for example, to find a mutant that has a high mutation rate—start with a strain of bacteria that has at least 4 selectable traits. Say, they don’t survive without threonine, don’t survive without isoleucine/valine, don’t survive penicillin, and don’t survive rifampicin. So you grow up a hundred billion or so of them and then you centrifuge them down and resuspend them in medium that doesn’t have threonine. Most of them die. Wait for the survivors to grow, and then centrifuge them down and resuspend them in medium that doesn’t have isoleucine/valine. Most of them die. Wait for the survivors to grow, and centrifuge them down and resuspend them in medium that has penicillin. Do it a fourth time with rifampicin. Plate them out on media that has lactose (when the originals couldn’t use lactose). Some of the colonies will be large and some small, pick a colony that has lots of little warts of bigger growth, because it gets lactose-using mutants even while the colony is growing. A strain that has a hundred times the mutation rate can be easily selected this way. It started out at frequency around 10^-8. After the first selection cycle it was frequency around 10^-6. By the fourth round it was common. Sometimes you can get a mutation rate around 1000 times the normal rate. Much above that and it doesn’t survive well.
Take one colony per try because you don’t want to test multiple colonies and then find out they’re the same mutation over again.
There are lots of examples of unexpected selective outcomes.
A story—a long time agon a swedish researcher tried to increase wheat yields by picking the biggest wheat kernels to plant. In only 5 generations he had a strain of wheat that produced 6 giant wheat kernels per stalk.
When scale insects were damaging citrus fruits, farmers tried to poison them with cyanide. They’d put a giant tent over the whole tree and pump in the cyanide and kill the scale insects. Plants can be immune to cyanide but no animal that depends on respiration can be. And yet in only 5 years or so they got resistant scale insects. The resistant insects would—when anything startling happen—sit very still and hold their breath for half an hour or so.
If you want to do directed evolution, you do better to do it in controlled conditions. Take your results and test them carefully and make sure they’re what you want before you release them. Microbiologists who want mutants for research commonly take 20 or 100 mutants who survive the conditions they’re selected to survive, and test until they get a few that appear to be just what they want. Eliminate the rest.
So, for example, to find a mutant that has a high mutation rate—start with a strain of bacteria that has at least 4 selectable traits. Say, they don’t survive without threonine, don’t survive without isoleucine/valine, don’t survive penicillin, and don’t survive rifampicin. So you grow up a hundred billion or so of them and then you centrifuge them down and resuspend them in medium that doesn’t have threonine. Most of them die. Wait for the survivors to grow, and then centrifuge them down and resuspend them in medium that doesn’t have isoleucine/valine. Most of them die. Wait for the survivors to grow, and centrifuge them down and resuspend them in medium that has penicillin. Do it a fourth time with rifampicin. Plate them out on media that has lactose (when the originals couldn’t use lactose). Some of the colonies will be large and some small, pick a colony that has lots of little warts of bigger growth, because it gets lactose-using mutants even while the colony is growing. A strain that has a hundred times the mutation rate can be easily selected this way. It started out at frequency around 10^-8. After the first selection cycle it was frequency around 10^-6. By the fourth round it was common. Sometimes you can get a mutation rate around 1000 times the normal rate. Much above that and it doesn’t survive well.
Take one colony per try because you don’t want to test multiple colonies and then find out they’re the same mutation over again.