Genetic Drift: Definition, Types, Examples and Process

Genetic drift is the change in the frequency of an existing allele in a population due to random mating. It can cause gene variants to disappear completely and lead to a reduction in genetic variation. It can also cause the rare allele to become much more frequent and even get fixed. When few other copies of an allele exist, the effect of genetic drift is more noticeable.

This Story also Contains

1. What is Genetic Drift?
2. Basics of Genetic Drift
3. Types of Genetic Drift
4. Genetic Divergence Between Populations
5. Genetic Drift vs Gene Flow
6. MCQs on Genetic Drift

But when many copies exist, the effect is much less notable. There were many debates in the mid-20th century over the relative importance of natural selection versus the other neutral process, including genetic drift. There are also views that genetic drift plays a role in evolution, which was the view for several decades. Genetic drift is an important topic of the chapter Evolution. It is an important chapter in the biology subject.

What is Genetic Drift?

Genetic drift is a process that causes changes in allele frequencies within a population. Its major sources are generally identified as chance events, especially in small populations. Unlike natural selection, which depends on differential survival and reproduction, genetic drift is a random process, which might sometimes result in the loss or fixation of alleles over time.

Another definition of genetic drift is its ability to change genetic patterns, hence affecting the evolutionary outcome of species or species with lower population sizes and isolated ones. For example, in a small population, a rare allele may become extinct due to random events. The element of randomness gives one much insight into how populations change through the evolutionary processes.

Basics of Genetic Drift

Genetic drift is an evolutionary process that is based on randomness. It causes the shifting of allele frequencies in a population because the survival and reproduction of individuals depend on chance events, hence producing fluctuations in allele frequencies among generations.

Genetic Drift Vs. Natural Selection

While both genetic drift and natural selection affect the evolution of a population, they work in different ways. For natural selection, survival and reproduction are contingent upon an allele's efficiency in enhancing these functions. Genetic drift, on the other hand, is a strictly random process, unrelated to allele efficiency. Both processes play crucial roles in the process of evolution, though they work in different ways.

Types of Genetic Drift

Bottleneck and Founder effects are the two theories that explain the process of genetic drift. Both processes are explained below-

Bottleneck Effect

The bottleneck effect involves the situation where an event, such as a natural disaster or disease, causes a massive reduction in population size. This drastic reduction in population limits the gene pool and thus the variation levels in genetic code decreases substantially. As an example, northern elephant seals have relatively low genetic variation levels today due to their population size dropping to less than 100 in the 19th century, while their current numbers are in the tens or thousands.

Founder Effect

The founder effect takes place when a small group of individuals breaks away from a larger population to form a new population. The small population, therefore, possesses only a fraction of the genetic diversity of the original population. For example, isolated populations such as the Amish contain less genetic variation and are therefore more prone to certain human genetic disorders.

Genetic Divergence Between Populations

Genetic drift also causes genetic divergence between populations, usually when they are isolated or separated geographically and are unable to interbreed. As time progresses, the actual random changes in allele frequencies create genetic differences, and this may eventually lead to speciation and evolution, depending on the degree of differentiation.

Genetic Drift vs Gene Flow

Genetic drift and gene flow are the evolutionary mechanisms that influence the allele frequencies in populations. But they operate in very different ways. The difference between genetic drift and gene flow is given below

MCQs on Genetic Drift

Q1. Variation in gene frequencies within populations can occur by chance rather than by natural selection. This is referred to as:

Option 1: Genetic load

Option 2: Genetic flow

Option 3: Genetic drift

Option 4: Random mating

Correct answer: 3) Genetic drift

Explanation:

Genetic drift - The term genetic drift refers to the estimation of the genes of certain traits when a section of the population migrates or dies of natural calamity. It alters the gene frequency of the remaining population.

Hence, the correct answer is option 3) Genetic drift.

Q2.Genetic drift is an evolutionary process in which the frequency of a given gene __________ varies randomly across a population.

Option 1: Allele

Option 2: Gene

Option 3: Both (1) and (2)

Option 4: None of the above

Correct answer: 1) Allele

Explanation:

Genetic drift, a fundamental evolutionary mechanism, describes the random fluctuations in the prevalence of gene alleles across populations, operating independently of natural selection. This process is particularly pronounced in small populations, where the influence of stochastic events during reproduction can significantly alter the frequency of alleles. It arises from random sampling, which may cause certain alleles to become more or less common over generations, potentially leading to the loss of genetic diversity or the fixation of particular alleles at specific loci.

Hence, the correct answer is option 1) Allele

Q3. Genetic drift has a stronger impact on small populations as compared to larger populations because:

Option 1: Small populations have more favorable variations.

Option 2: Small populations experience higher mutation rates.

Option 3: Genetic drift is a random process and chance events can have a greater effect on small populations.

Option 4: Small populations have a higher gene flow with other populations.

Correct answer: 3) Genetic drift is a random process and chance events can have a greater effect on small populations.

Explanation:

Genetic drift is a random process that occurs due to chance events rather than natural selection. In small populations, the effect of genetic drift is more pronounced because chance events can have a greater impact on the gene frequencies. With fewer individuals, the random loss or fixation of alleles can occur more easily, leading to significant changes in the genetic makeup of the population. In larger populations, the effects of genetic drift are diluted due to a larger gene pool and a higher chance of preserving genetic diversity through reproduction.

Hence, the correct answer is option 3) Genetic drift is a random process and chance events can have a greater effect on small populations.

Also Read

• MCQ Practice on Embryology

• Miller Urey Experiment

• Difference between Homologous and Analogous Structures