Genetic drift, also known as Sewall Wright effect, is a fundamental mechanism of evolution, particularly significant in smaller populations. It refers to random fluctuations in the frequency of alleles (gene variants) within a population, occurring purely by chance, independent of any selective advantage. Unlike natural selection, which favors traits that increase survival and reproduction, genetic drift is a non-adaptive process. Understanding genetic drift is vital as it can lead to the loss of genetic diversity and potentially impact a population’s ability to adapt to changing environmental conditions, especially pertinent in the context of conservation efforts and understanding human evolution. What is Genetic Drift? Genetic drift is a stochastic (random) process that alters allele frequencies in a population over time. It's a consequence of chance events in survival and reproduction. Imagine flipping a coin repeatedly – even if the coin is fair (50/50 chance), you won’t always get exactly 50% heads and 50% tails in every flip. Similarly, allele frequencies can deviate randomly from expected values, especially in small populations. Mechanisms of Genetic Drift Two primary scenarios illustrate genetic drift: Bottleneck Effect: A sudden reduction in population size due to events like natural disasters, disease outbreaks, or human activities (e.g., habitat destruction). This drastically reduces genetic diversity, as only the alleles present in the surviving population are passed on. Founder Effect: Occurs when a small group of individuals colonizes a new area, establishing a new population. The allele frequencies in this new population may differ significantly from the original population simply due to the random sample of alleles carried by the founders. Consequences of Genetic Drift Genetic drift has several significant consequences: Loss of Genetic Diversity: The most prominent consequence. As alleles are lost randomly, the population becomes less adaptable to environmental changes. Fixation of Deleterious Alleles: Even harmful alleles can become fixed (reach a frequency of 100%) by chance, especially in small populations, reducing fitness. Increased Genetic Differences Between Populations: Populations isolated from each other experience independent genetic drift, leading to divergence in their genetic makeup. Reduced Effectiveness of Natural Selection: Genetic drift can counteract the effects of natural selection, preventing beneficial alleles from becoming more common. Distinction from Natural Selection Feature Genetic Drift Natural Selection Driving Force Random Chance Differential Survival & Reproduction Adaptation Non-adaptive Adaptive Population Size More impactful in small populations Impactful in all population sizes Effect on Diversity Reduces diversity Can increase or decrease diversity depending on selection pressure Examples and Case Studies Cheetahs: The modern cheetah population exhibits extremely low genetic diversity, believed to be a result of a severe population bottleneck event approximately 10,000 years ago. This lack of genetic variation makes them vulnerable to diseases and environmental changes. Amish Communities: Certain genetic disorders, like Ellis-van Creveld syndrome (characterized by dwarfism and polydactyly), are more prevalent in Amish communities due to the founder effect. A single individual carrying the recessive allele founded the community, leading to a higher frequency of the disorder. Government Schemes & Relevance While there aren’t specific schemes directly addressing genetic drift, the National Biodiversity Authority (NBA) , established under the Biological Diversity Act, 2002, plays a crucial role in conserving genetic resources and mitigating the effects of population bottlenecks and founder effects on native species. Its mandate includes in-situ and ex-situ conservation efforts. In conclusion, genetic drift is a powerful evolutionary force, particularly impactful in small populations, leading to random fluctuations in allele frequencies and a loss of genetic diversity. While distinct from natural selection, it remains a critical mechanism shaping the genetic makeup of populations. Understanding genetic drift is essential for conservation efforts, managing endangered species, and deciphering the complexities of evolutionary history. Continued research and monitoring are vital to mitigate its potentially detrimental effects and preserve biodiversity.

Genetic Drift: Principles and Implications | UPSC Mains ANI-HUSB-VETER-SCIENCE-PAPER-I 2011

Genetic Drift.

How to Approach

This question requires a clear explanation of genetic drift, its mechanisms, and its implications. The approach should start with a concise definition and then delve into the workings of genetic drift, differentiating it from natural selection. Discussing the impact on small populations and the potential for loss of genetic diversity is crucial. Finally, illustrating with examples will enhance the answer's clarity and demonstrate understanding. A structured format with clear headings will aid in comprehension and presentation.

Genetic drift, also known as Sewall Wright effect, is a fundamental mechanism of evolution, particularly significant in smaller populations. It refers to random fluctuations in the frequency of alleles (gene variants) within a population, occurring purely by chance, independent of any selective advantage. Unlike natural selection, which favors traits that increase survival and reproduction, genetic drift is a non-adaptive process. Understanding genetic drift is vital as it can lead to the loss of genetic diversity and potentially impact a population’s ability to adapt to changing environmental conditions, especially pertinent in the context of conservation efforts and understanding human evolution.

What is Genetic Drift?

Genetic drift is a stochastic (random) process that alters allele frequencies in a population over time. It's a consequence of chance events in survival and reproduction. Imagine flipping a coin repeatedly – even if the coin is fair (50/50 chance), you won’t always get exactly 50% heads and 50% tails in every flip. Similarly, allele frequencies can deviate randomly from expected values, especially in small populations.

Mechanisms of Genetic Drift

Two primary scenarios illustrate genetic drift:

Bottleneck Effect: A sudden reduction in population size due to events like natural disasters, disease outbreaks, or human activities (e.g., habitat destruction). This drastically reduces genetic diversity, as only the alleles present in the surviving population are passed on.
Founder Effect: Occurs when a small group of individuals colonizes a new area, establishing a new population. The allele frequencies in this new population may differ significantly from the original population simply due to the random sample of alleles carried by the founders.

Consequences of Genetic Drift

Genetic drift has several significant consequences:

Loss of Genetic Diversity: The most prominent consequence. As alleles are lost randomly, the population becomes less adaptable to environmental changes.
Fixation of Deleterious Alleles: Even harmful alleles can become fixed (reach a frequency of 100%) by chance, especially in small populations, reducing fitness.
Increased Genetic Differences Between Populations: Populations isolated from each other experience independent genetic drift, leading to divergence in their genetic makeup.
Reduced Effectiveness of Natural Selection: Genetic drift can counteract the effects of natural selection, preventing beneficial alleles from becoming more common.

Distinction from Natural Selection

Feature	Genetic Drift	Natural Selection
Driving Force	Random Chance	Differential Survival & Reproduction
Adaptation	Non-adaptive	Adaptive
Population Size	More impactful in small populations	Impactful in all population sizes
Effect on Diversity	Reduces diversity	Can increase or decrease diversity depending on selection pressure

Examples and Case Studies

Cheetahs: The modern cheetah population exhibits extremely low genetic diversity, believed to be a result of a severe population bottleneck event approximately 10,000 years ago. This lack of genetic variation makes them vulnerable to diseases and environmental changes.
Amish Communities: Certain genetic disorders, like Ellis-van Creveld syndrome (characterized by dwarfism and polydactyly), are more prevalent in Amish communities due to the founder effect. A single individual carrying the recessive allele founded the community, leading to a higher frequency of the disorder.

Government Schemes & Relevance

While there aren’t specific schemes directly addressing genetic drift, the National Biodiversity Authority (NBA), established under the Biological Diversity Act, 2002, plays a crucial role in conserving genetic resources and mitigating the effects of population bottlenecks and founder effects on native species. Its mandate includes in-situ and ex-situ conservation efforts.

Additional Resources

Key Definitions

Allele

One of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.

Founder Effect

Occurs when a small group of individuals separates from a larger population to establish a new population, resulting in a reduced genetic diversity in the new population.

Key Statistics

The cheetah population has approximately 3-5% of the genetic variation found in chimpanzees. This low genetic diversity makes them exceptionally vulnerable to disease and environmental changes.

Source: IUCN Red List

The Amish population in North America, descended from approximately 200 founding families, exhibits a prevalence of Ellis-van Creveld syndrome at around 1 in 10,000, significantly higher than the general population.

Source: Genetic and Rare Diseases Information Center (GARD)

Examples

Island Fox Example

The island fox of the Channel Islands off the coast of California experienced a severe bottleneck in the 1990s due to canine distemper virus. This drastically reduced genetic diversity, making the foxes vulnerable to further threats.

Frequently Asked Questions

▶How does genetic drift differ from mutation?

Mutation introduces new alleles, while genetic drift changes the frequency of existing alleles randomly. Mutation is a source of variation; genetic drift acts on that existing variation.