Genetic drift

Also known as genetic derivation or oscillation, genetic or allelic drift, genetic drift comprises the diversity of the genetic background of populations. The occurrence of this occurs in line with natural selection, which as a rule is a consequence of chance.

Random procedure, this exercises function on groups of individuals, promoting the allelic alteration (gene pool) of these and the ascendancy of certain characteristic aspects in these. However, even though it is an evolutionary process, genetic drift is not capable of producing adaptation.

This affects the most diverse population groups, but while the population is small, the more instantaneous and energetic the effect caused by genetic derivation will be. This consequence may be the existence of some adversity for the breeds that may be in extinction.

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Allele frequencies

Alleles are affected by drift for short periods. With occasional occurrences, the allelic rhythms increase or decrease whereas, when the frequency of only one allele portrayed in the population arrives – or even the absence of this one -, they can be classified as allele fixation or extinction.

If an allele frequency reaches 1, only through mutation, it becomes liable to undergo a new change, if the isolation of the population remains active.

There is also the possibility that this frequency may change due to the migration process, in which new human beings apply an allelic diversity to the group of individuals.


The size of a given population is a determining factor for the conservation of an allele. That is, in small groups of individuals, the existence of reduced generations already makes possible the occurrence of allelic fixation, based on gene drift. In larger groups, the derivation should take longer.

Very rarely it is possible to have, independently of one another, genetic derivation and natural selection, as these have constant performance in a group of human beings. However, the level at which alleles can be affected by these events varies depending on the circumstances.

If a population group is large, the genetic drift occurs slowly, while the phenomenon of selection can occur in the opposite way: fast on an allele and, thus, being able to increase or decrease its frequency.

In a population whose size is smaller, gene drift occurs in supremacy. Thus, in this context, natural selection occurs in a timid and noteworthy manner.

In cases in which the size of a population group suffers a sudden reduction and is restricted to just one generation, this is considered the bottleneck period – bottleneck -, which can cause considerable loss of genetic variation even if this period comes to an end. be brief, passing through a few generations. Autonomous to natural selection, these cases can lead to the elimination of positive adaptations in the group of individuals.

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