Genetic drift, also known as genetic sampling error or the Sewall Wright effect, is a shift in a small population's gene pool that occurs entirely by chance. Without regard for the survival or reproductive value of the alleles involved, genetic drift can result in genetic features being lost from a population or becoming ubiquitous in a population. Genetic drift is a random statistical process that can only occur in tiny, isolated populations where the gene pool is small enough for chance occurrences to significantly alter the population's makeup. Unless it is physiologically unfavorable, every particular allele shared by a high number of people in a population is almost guaranteed to be transmitted by some of them.
Genetic drift arises from the fact that a subsample (i.e., tiny, isolated population) produced from a large sample set (i.e., population) is not always representative of the larger set. As one might imagine, the smaller the population, the higher the risk of sampling error (or misrepresentation of the wider population) and, as a result, considerable amounts of drift in any one generation. Drift over generations can result in the full loss of one allele in an allele pair, in which case the surviving allele is considered to be fixed.
What factors contribute to genetic drift?
Even though genetic drift is a result of chance, it is important to understand how it is influenced by a variety of factors, including the number of individuals in the population (the effect of genetic drift is more prevalent in small populations), and the number of individuals contributing to genetic drifting (some individuals do not produce offspring). Another element that impacts population growth is the incidence of natural catastrophes; as a result, these disasters will enhance the relevance of random genetic drift among the population as well as changes in natural gene flow patterns. When people reside in nonurban areas, habitat fragmentation is one of the key factors that impact gene drift, causing nonhuman communities to disperse or perhaps become extinct. As a result, gene flow between these groups has diminished, but gene drift has increased.
Consequences of Genetic Drift
What function does genetic drift play in evolution? Fixation of particular genes may be similar to their initial frequency in the population, resulting in a loss of variety in the genetic pool. Another effect of genetic drift is an increase in population differentiation, where different populations of the same species may have different alleles as a result of genetic drifting. This occurs when the frequency of one allele is fixed in one population but decreases in another population as the frequencies of alleles in the genetic pool move in opposite directions.
Small populations can experience higher fluctuations in allele frequencies due to sampling error than large populations. Because the gene pool of big populations tends to be more stable, alleles in small populations are fixed more quickly than in large populations. Large populations, on the other hand, are affected by genetic drift when they become small as a result of a natural disaster that drastically reduces population size until conditions improve and allow the population to grow again (bottleneck effect) or when a small population leaves the group to start a new colony when the population is threatened (founder effect). To keep a small population from going extinct, genetic diversity must be preserved. As a result, genetic drift must be reduced, and mutation must be preserved to allow for adaptability.
Different Types of Genetic Drift
The genetic drift effect is unaffected by an allele's advantages, because a detrimental allele can be fixed whereas a favorable allele can be lost by chance. When a population is subjected to a natural catastrophe (bottleneck effect) or when a group of people splits from a population (founder effect), uncommon recessive genes might become increasingly frequent due to the effect of genetic drift. The influence of genetic drift manifests strongly in small populations. We'll go through the bottleneck effect vs. founder impact in more detail:
Population bottleneck
What is the Bottleneck Effect, and how does it work? The bottleneck effect is defined as a reduction in the number of people in a population as a result of a natural disaster. The bottleneck effect of genetic drift frequently changes the genetic distribution among the population, making the effect of genetic drift more substantial. When a result, as the number of mating individuals decreases, genetic variety among this group will diminish. When the rate of genetic drift in a population rises, it leads to the loss or fixation of certain alleles; this process is referred to as a reduction in the genetic effective size.
Despite the fact that populations experiencing a bottleneck may reproduce and grow in size again, genetic variation among these populations continues to decline at a rate proportional to the size of the disaster until new individuals are introduced into the population through migration or new mutations occur. The magnitude and length of the bottleneck have an impact on its biological strength; these parameters are computed quantitatively to assess the bottleneck's impact on the population's genetic variety.
Founder effect
The founder effect is defined in biology as the formation of a small population when a small number of individuals leave their population to start a new colony; these individuals do not necessarily cover the entire genetic set of the population, so gene drifting is significant within this small population.
The founder effect is most typically seen in fungus, where spores disseminate and colonize in new settings, generating new colonies that may or may not contain the same alleles as the population from which they were derived.
Genetic Drift in Evolution
Genetic drift contributes to the increase or decrease of a specific allele in each population; thus, in normal populations, the effect of genetic drift is canceled over time; however, if an allele frequency has reached zero, the effect of genetic drift cannot be canceled unless a mutation produces this allele again.
In evolution, genetic drift is crucial because it decides the fate of a mutation, whether it will vanish or become fixed in the population after a few generations. Even for common genes, genetic drift is relevant in nonideal populations of small size.
If an allele is fixed in one generation, it is usually expected to grow in subsequent generations. In terms of genetic drift, however, what happens in one generation does not always happen in subsequent generations, thus if one allele rises in one generation, it may increase or decrease in subsequent generations.
A subdivided population adaptation is a two-phase process characterized by genetic drifting, in which some alleles are lost or fixed by chance, allowing the population to explore new genes. The second phase is characterized by natural selection of the most beneficial genes introduced in phase one, with these genes being exported to other populations via migration. In the evolutionary process of people, the balance between mutations and gene wandering generates a state of genetic variety, according to the genetic drift theory. Because mutations create new alleles, gene drifting can either delete or correct these new alleles.