What is a good mutation

Mutation, positive: examples

Positive mutations are mutations that increase the fitness of an individual, i.e. the number of offspring compared to the average number of offspring in the population. In contrast to neutral or harmful mutations, positive mutations are very rare. Nevertheless, they are the engine of evolution. In the following I would like to present two examples of positive mutations that I found during my research on the spectrum pages.

Mutation of the gene for the sodium channel in garter snakes

Many animals use highly toxic substances to protect themselves against predators, including newts. Your skin contains tetrodotoxin (TTX), a nerve toxin that quickly leads to death from respiratory paralysis. Tetrodotoxin blocks the electrically controlled sodium channels in nerve cells. When these are blocked, action potentials can no longer arise and the muscles supplied by the nerve cell no longer receive any impulses: paralysis.

Now there are a number of snakes in California that still eat such newts. To find out why these snakes are resistant to the venom, American scientists (GEFFENEY and colleagues from Utah State University) studied four populations of the American garter snake (Thamnophis sirtalis). One of the four populations was not resistant to tetrodotoxin; these animals did not eat the newts. The other three populations were resistant to varying degrees. The scientists suspected a mutation in the gene for the sodium channel and examined the DNA of individuals from all four populations. Indeed, the individuals in the three resistant populations all had a mutation in the gene for the sodium channel. The scientists were quite surprised when it turned out that only a single amino acid had to be exchanged in order to make the sodium channel insensitive to the toxin. By exchanging this one amino acid, the binding site for the tetrodotoxin changes so that it can no longer attach itself to the sodium channel (key and lock principle).

Source: Spektrum direkt, "Aggressive Beute", April 8, 2005

Mutation of the gene for the sodium channel in mussels

Mussels are often colonized by parasites: cyanobacteria or dinoflagellates, which release the toxin saxotoxin. When eating such mussels, very dangerous mussel poisoning can occur.

However, in areas where dinoflagellate infestations are more common, there are mussels that are resistant to the saxotoxin. Studies have shown that the saxotoxin, like tetrodotoxin (see example above), blocks the sodium channel of the nerve cells. Mutations in the gene of the sodium channel have now also been detected in the resistant mussels, which successfully prevent the toxin from docking.

Source: Spektrum direkt, "Mutation makes mussels resistant to natural toxins", April 8, 2005