Neutral theory of molecular evolution

The neutral theory of molecular evolution (English neutral theory of molecular evolution ) is a partial aspect of the theory of evolution. The key finding is that most genetic changes with respect to the natural selection are neutral, the individual so there are no direct advantages or disadvantages. It follows that random events such as genetic drift in the evolution of genetic information play a much greater role than such changes, which are driven by selection. However, the neutral theory of molecular evolution includes keeping the meaning selection- driven changes for specific gene sequences explicitly not. While these sequences for the observable and therefore selectable phenotype may play a major role, but they make up only a small part of the genetic information.

The neutral theory of molecular evolution was founded in the late 60s by Motoo Kimura.

Causes and occurrence of neutral mutations

Various modifications of the genome can lead to selection- neutral mutations. Firstly, the genetic code is degenerate, so that changes in the nucleic acid sequence does not necessarily lead to changes in the amino acid sequence of a protein. In addition, many amino acid substitutions on the basis of similar properties for the form and function of a protein are largely neutral. In addition, large portions of most genomes do not code for proteins.

Compare various protein-coding genes in humans and various rodents showed that the rate of synonymous mutations, ie those in which the amino acid sequence does not change, is considerably higher than the rate of non- synonymous mutations, ie those that are not neutral.

The rate of mutation in sequences that do not code for proteins above: in the intron of the gene for insulin, the mutation rate is about 6 times higher than in the two exons. This can be explained by the fact that those sections much less the subject than the protein-coding selection. Synonyms mutations are equally common in different lineages of mammals, while non- synonymous mutations as in primates are much less frequent than in rodents. Is highest mutation rate in pseudogenes, which are not transcribed.

Importance

An important implication of the neutral theory is that neutral mutations, at least within a similar life forms, take place at a constant rate. Here we find the concept now often used in evolutionary studies of the molecular clock.

To understand the mechanisms of evolution, the neutral theory plays a role, particularly in the explanation of evolvability ( evolvability ) or the capacity for self- adaptation (self - adaptability ). Since neutral mutations do not alter the biological fitness under the given conditions, can vary characteristics that are relevant to changing environmental conditions for the selection by them. Can also influence the potential for subsequent, selection- relevant change selection- neutral mutations. So, for example, encode 9 different nucleic acid triplets encoding the amino acid arginine. CGA is the probability that, for a point mutation further Arginine is encoded, 4/9. AGA, however, is the likelihood 2, / 9th Despite a neutral effect on the phenotype that is a mutation of the first base changes the potential of a further mutation affecting the Phänoptyp.

History

The neutral theory was formulated in the 1960s by Motoo Kimura. He had found out by comparing the amino acid sequences of proteins in different species that the evolution rate of the amino acid sequences of some proteins is constant. This constancy can not be explained by selection, but only by the genetic drift. It represented a counterweight to the then widespread view, each mutation is important for the selection. However, it was emphatically not a counter-proposal to the theory of natural selection, but an extension.

The title of an article by JL King and TH Jukes, Non- Darwinian Evolution in Science (Volume 164, 1969, pp. 788 ff ), however, led to a discussion of whether the neutral theory and the molecular theory of evolution of Darwin's coinage generally not in question provide. However, it was soon clear that this is not the case. However, they show that not all mutations are subject to the selection ( so-called silent mutations).

In the so-called neutralist - selectionists debate, it was first necessary, if there are neutral mutations at all. This is now generally accepted. Discussed is still, how great is the proportion of neutral mutations.