Содержание
- 2. INTRODUCTION A population bottleneck or genetic bottleneck is a sharp reduction in the size of a
- 4. When disaster strikes, an ecosystem can change very quickly. When an event causes a drastic decrease
- 5. Population size matters Larger populations are unlikely to change this quickly as a result of genetic
- 6. EXAMPLES OF BOTTLENECK EFFECT The original population of black robins on the left had genetic variation
- 7. In the aftermath of the bottleneck event, and with the help of conservation scientists, the remaining
- 8. Toba catastrophe theory The controversial Toba catastrophe theory, presented in the late 1990s to early 2000s,
- 9. Recent research shows the extent of climate change was much smaller than believed by proponents of
- 10. Bottleneck Effect Two reasons for change: Surviving population members have different allele frequencies than original population
- 11. Examples of the Bottleneck Effect
- 14. Bottleneck effect Subpopulation caused when a natural disaster reduces the size of an original larger population.
- 15. A population bottleneck can be split into three unique stages: Before it occurs: Before a chance
- 17. Selective breeding Bottlenecks also exist among pure-bred animals (e.g., dogs and cats: pugs, Persian) because breeders
- 18. Disaster Events and Allele Frequency Genetic drift can be separated into two types. The founder effect
- 19. An example of this in the real world happened to northern elephant seals. In the 19th
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INTRODUCTION
A population bottleneck or genetic bottleneck is a sharp reduction in the size of a population due
INTRODUCTION
A population bottleneck or genetic bottleneck is a sharp reduction in the size of a population due
When disaster strikes, an ecosystem can change very quickly. When an event causes
When disaster strikes, an ecosystem can change very quickly. When an event causes
This can be caused by a natural disaster, like an earthquake or volcano eruption. Today, it is also often caused by humans through over-hunting, deforestation, and pollution.
When most members of a population die suddenly, genetic variation goes down and the frequencies at which different alleles are found in the population can change in a big way. Remember that alleles are different forms of a specific gene located in the same place on a chromosome.
Population size matters
Larger populations are unlikely to change this quickly
Population size matters
Larger populations are unlikely to change this quickly
EXAMPLES OF BOTTLENECK EFFECT
The original population of black robins on
EXAMPLES OF BOTTLENECK EFFECT
The original population of black robins on
In the aftermath of the bottleneck event, and with the help
In the aftermath of the bottleneck event, and with the help
The important detail that makes this an example of a bottleneck event and not just natural selection is that the birds survived at random. If there were some heritable traits that allowed some birds to survive better than others, then it would be an example of natural selection.
Toba catastrophe theory
The controversial Toba catastrophe theory, presented in the late 1990s
Toba catastrophe theory
The controversial Toba catastrophe theory, presented in the late 1990s
However, subsequent research, especially in the 2010s, appeared to refute both the climate argument and the genetic argument
Recent research shows the extent of climate change was much smaller
Recent research shows the extent of climate change was much smaller
Finally, such coalescence would not, in itself, indicate a population bottleneck, because mitochondrial DNA and Y-chromosome DNA are only a small part of the entire genome, and are atypical in that they are inherited exclusively through the mother or through the father, respectively. Genetic material inherited exclusively from either father or mother can be traced back in time via either matrilineal or patrilineal ancestry.
In 2000, a Molecular Biology and Evolution paper suggested a transplanting model or a 'long bottleneck' to account for the limited genetic variation, rather than a catastrophic environmental change. This would be consistent with suggestions that in sub-Saharan Africa numbers could have dropped at times as low as 2,000, for perhaps as long as 100,000 years, before numbers began to expand again in the Late Stone Age.
Bottleneck Effect
Two reasons for change:
Surviving population members have different allele
Bottleneck Effect
Two reasons for change:
Surviving population members have different allele
When population is small, genetic drift reduces genetic variation faster, Alleles could even get eliminated
Examples of the Bottleneck Effect
Examples of the Bottleneck Effect
Bottleneck effect
Subpopulation caused when a natural disaster reduces the size of
Bottleneck effect
Subpopulation caused when a natural disaster reduces the size of
Result of habit fragmentation and/or overexploitation of the species.
Bottleneck effects v/s Founder effects
Founder effects
Founder establishes a subpopulation as a new colony drawn from a larger population.
Result of migration .
A population bottleneck can be split into three unique stages:
Before it
Before it
A chance event occurs: The effect is prompted by some kind of chance event. Usually, this is a natural disaster like a forest fire or an earthquake. The event severely decreases the size of the population. Which members survive is based on chance.
Decreased genetic diversity: Because only some members of the population survive, only their alleles survive as well. The chance event leads to a loss of genetic diversity in the population. While the population can grow back to its original size, it will not have the same genetic diversity that it did before the event.
Selective breeding
Bottlenecks also exist among pure-bred animals (e.g., dogs and cats: pugs, Persian) because breeders limit
Selective breeding
Bottlenecks also exist among pure-bred animals (e.g., dogs and cats: pugs, Persian) because breeders limit
Selective breeding for dog breeds caused constricting breed-specific bottlenecks. These bottlenecks have led to dogs having an average of 2-3% more genetic loading than gray wolves. The strict breeding programs and population bottlenecks have led to the prevalence of diseases such as heart disease, blindness, cancers, hip dysplasia, cataracts, and more.
Selective breeding to produce high-yielding crops has caused genetic bottlenecks in these crops and has led to genetic homogeneity. This reduced genetic diversity in many crops could lead to broader susceptibility to new diseases or pests, which threatens global food security.
Disaster Events and Allele Frequency
Genetic drift can be separated into two
Disaster Events and Allele Frequency
Genetic drift can be separated into two
An event which could cause this effect on a population varies. It could be hunting, an environmental disaster, or even a disease. The important distinction between this effect and natural selection is that the bottleneck decreases a population at random. Natural selection is based on specific traits.
An example of this in the real world happened to northern
An example of this in the real world happened to northern