Genetic drift

As genetic drift (genetic drift, the drift is driving down German word related to the German, also Alleldrift or Sewall Wright effect called ) is called in population genetics a random change in gene frequency within the gene pool of a population. Genetic drift is a factor of evolution. A quantitative extension represents the Antigenic shift, to be replaced in whole segments of genes together. This has often particularly pronounced functional and qualitative changes result.

Genetic drift and Antigenic shift represent a kind of complement to natural selection represents the natural selection has no influence on the random change in the gene frequency of a population, but is directly linked to the survival and reproductive success of individuals, so their adequacy to their environment. The genetic drift or shift, however, has no such causes, but is purely determined at random ( stochastic).

Since a random change in gene frequency falls statistically more significant in smaller populations that provide genetic drift and Antigenic shift is an important factor in the evolution of founder populations and thus the speciation; they do based on the fact that a truncated random population that lives in a particular area, only a small subset of the possible gene frequencies has that also in another relationship to each other than in the general population. The evolutionary development of this population depends on these shifted gene frequencies.

The bottleneck can effect a particular type of genetic drift is referred to, in which the population size is greatly reduced by a fortuitous event, thereby reducing the variability occurring in the population. Allele frequencies after differ mostly from those of the original population, the reduced variation ( polymorphism ) increases the susceptibility to disease and complicates future adaptive changes.

Genetic drift can also occur in larger panmictic populations, after being divided into smaller sub-populations. Condition are random change of genes and transfer of modified genes. Genetic drift can cause phenotypic changes, but it does not.

Meaning extension: the dissemination of such changes in larger populations is referred to as genetic drift. Today is known as genetic drift and the intrusion deliberately or accidentally altered genes in other areas.

Gene frequencies

From the perspective of population genetics, the genetic drift is a likely effect. The genes that are passed on to the next generation, are not a complete copy of the genes of the successful members of the parent generation. They are a random (stochastic ) selection, a sample with random fluctuations. By means of random statistical fluctuations in the composition of the gene frequency differs from that in the parent population of the children in the population. The gene frequencies in the gene pool have drifted. Genetic drift is more noticeable, the smaller the population. This statistical causes. Example: When throwing of coins heads or tails appear, on average, with the same probability. But with only a few litters, it is unlikely that heads and tails appear to be exactly the same frequency. The greater the number of litters, the closer you a ratio of 50: 50 Therefore, the fluctuations in gene frequencies are larger than in populations with many individuals in small populations ( effective population size).

Drifting alleles often have a limited lifetime. If the frequency of an allele in the successive generations of strong increases or decreases, then an allele in the population disappear completely or it will be the only allele in the population ( fixation). The genetic diversity is reduced, depleted the gene pool.

Genetic drift and Antigenic shift towards natural selection

Genetic drift and Antigenic shift and natural selection are evolutionary factors and act simultaneously. Through them, the composition of the gene pool changes. The frequency of alleles ( gene variations ) and thus the predominant phenotypic characteristics in a population change over time. In genetic drift and Antigenic shift the change in the frequency of alleles is independent of whether they are beneficial or detrimental effect on the phenotype. Genetic drift is to be considered random and independent of the genetic fitness. In contrast, those phenotypic traits in natural selection and thus favors those alleles that increase the genetic fitness. In large populations, in which genetic drift is small, the natural selection is even at a low selection pressure have the greater amount of change in gene frequencies. In small populations, however, the larger statistical fluctuations are superimposed by the genetic drift that changes the selection.

Antigenic shift and genetic drift in populations

Antigenic shift and genetic drift can have profound and often bizarre effects on the evolutionary history of a population. This can even lead to the extinction of a population. If a population shrinks to a small size and then grows again ( it is believed that this has happened throughout human evolutionary history ), then the genetic drift can lead to sudden and dramatic changes in gene frequency, independently of natural selection. On such occasions many beneficial adaptations may be lost ( genetic bottleneck ). With a genetic bottleneck associated gene defects are sometimes compensated by purging partially.

Similarly, the founder effect comes in, for example, migratory populations, in which only a few individuals with a rare Allelzusammensetzung form the starting point of a new population. Here, the gene frequencies can be in contradiction with the previous natural selection. The founder effect is sometimes blamed for the increased incidence of genetic diseases.

Antigenic shift in virology

Some viruses are genetically very unstable, eg HIV and the causative agent of influenza and "viral " colds. Genshifts in influenza viruses that the starting point of a pandemic like the Spanish flu of 1918 and the Asian flu of 1957.