Bottleneck Effect - Definition, Causes, Example, & Effects of Bottleneck Effect

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1) Definition of Bottleneck Effect
2) Causes of Bottleneck Effect
3) An example of a Bottleneck Effect
4) Effects of Bottleneck Effect
5) MCQs
6) Summary:
7) You may also like to learn:

Definition of Bottleneck Effect

The Bottleneck Effect is an utmost example of genetic drift that occurs when the size of a population is severely decreased. Events like natural catastrophes (earthquakes, floods, fires) can annihilate a population, eliminating most individuals and leaving behind a small, random selection of survivors.

The allele frequencies in this group may be extremely different from those of the population prior to the occasion, and some alleles might be missing out on entirely. The smaller-sized population will likewise be more prone to the effects of genetic drift for generations (till its numbers return to normal), possibly triggering even more alleles to be lost.

Population bottlenecks occur when a population’s size is minimized for at least one generation. Since genetic drift acts quicker to decrease genetic variation in small populations, going through a bottleneck effect can lower a population’s genetic variation by a lot, even if the bottleneck effect does not last for many generations. Decreased genetic variation means that the population might not have the ability to adjust to new selection pressures, such as weather modification or a shift in readily available resources, because the hereditary variation that selection would act upon might have already drifted out of the population.

Causes of Bottleneck Effect

When catastrophe strikes, a community can alter really rapidly. When an occasion triggers an extreme decrease in a population, it can cause a type of genetic drift called a bottleneck effect. This can be caused by a natural disaster, like an earthquake or volcano eruption. Today, it is likewise frequently caused by humans through over-hunting, deforestation, and contamination.

When most members of a population drop dead, genetic variation decreases, and the frequencies at which different alleles are found in the population can change in a big way. Bear in mind that alleles are different kinds of a particular gene situated in the same location on a chromosome.

An example of a Bottleneck Effect

Northern elephant seals have reduced genetic variation probably because of a population bottleneck effect humans inflicted on them in the 1890s. Hunting and killing lowered their population size to as few as 20 individuals at the end of the 19th century. Their population has given that rebounded to over 30,000– but their genes still carry the marks of this bottleneck effect: they have much less genetic variation than a population of southern elephant seals that were not so extremely hunted.

Further Reading: Vertebrate Axis Development

Effects of Bottleneck Effect

Population bottlenecks causing an extreme reduction of the population size are common in the evolutionary dynamics of natural populations; their incident is understood to have implications for genome development due to genetic drift, the ensuing reduction in genetic variation, and the rate of adaptation. Genetic bottleneck effects are evolutionary occasions that decrease the genetic variation of a population in a stochastic manner and result in founding populations that can lead to genetic drift.

In nature, the genetic bottleneck effect may take place at various points throughout the life cycles of RNA viruses. For example, transmission events, both horizontal and vertical, and systemic infections represent occasions in the infection life process that might impose a bottleneck effect.

Population bottlenecks play a crucial function in conservation biology and the context of agriculture (biological and pest control). In conservation biology, minimum viable population (MVP) size assists in determining the reliable population size when a population is in danger of extinction. The effects of a population bottleneck frequently depend on the variety of individuals remaining after the bottleneck effect and how that compares to the minimum viable population size.

MCQs

1. What is the Bottleneck Effect?

A. A surge in genetic variation
B. An increase in population size
C. A decrease in population size leading to genetic drift
D. A natural catastrophe that enhances genetic diversity
Answer: C

2. When does the Bottleneck Effect occur?

A. When the population size increases
B. When genetic variation is high
C. When a population’s size is severely decreased for at least one generation
D. During periods of stable environmental conditions
Answer: C

3. What events can lead to the occurrence of the Bottleneck Effect?

A. Overpopulation
B. Human activities like hunting and deforestation
C. Long periods of stability in the environment
D. High genetic variation
Answer: B

4. How do allele frequencies change during the Bottleneck Effect?

A. They remain constant
B. They become more unpredictable
C. They shift randomly due to the survival of a small group of individuals
D. They increase with population size
Answer: C

5. Why is a smaller-sized population more prone to genetic drift after a bottleneck?

A. Due to increased environmental stability
B. Because genetic drift acts slower in small populations
C. The smaller size allows for faster genetic drift, impacting genetic variation
D. Small populations are less affected by genetic drift
Answer: C

6. What can happen to a population’s genetic variation after experiencing a Bottleneck Effect?

A. It remains the same
B. It increases
C. It decreases significantly
D. It becomes more unpredictable
Answer: C

Summary:

The Bottleneck Effect, an extreme manifestation of genetic drift, occurs when a population undergoes a severe decrease in size, often due to natural catastrophes or human activities like over-hunting and deforestation. This leads to the survival of a small, random group of individuals, causing significant changes in allele frequencies compared to the original population. The resulting reduced genetic variation poses challenges for populations to adapt to new selection pressures.

Population bottlenecks, characterized by a minimum viable population size, play a crucial role in conservation biology and agriculture. The bottleneck effect, impacting genome development through genetic drift, can have long-term consequences on evolutionary dynamics. A notable example is the bottleneck effect experienced by Northern elephant seals in the 1890s, which, despite a population rebound, still carries genetic marks from the event.

Key Points:

The Bottleneck Effect results from a severe population decrease.
Natural catastrophes and human activities contribute to bottleneck occurrences.
Genetic drift during bottlenecks leads to significant changes in allele frequencies.
Reduced genetic variation challenges populations to adapt to new selection pressures.
Minimum viable population size is crucial in conservation biology and agriculture.
The bottleneck effect has long-term consequences on genome development and evolution.