AP Biology › Understanding Genetic Drift, Bottleneck Effect, and Founder Effect
For natural selection to occur, which of the following must be true of a population?
Phenotypic variations must be based on genetic variations
Having many populations in one area
Must be capable of sexual reproduction
Food is not available
The population must be isolated
Natural selection is one of the basic mechanisms of evolution, along with mutation, migration, and genetic drift. Phenotypic variations must be based on genetic variations rather than on varying environmental conditions to be considered an aspect of natural selection. While sexual reproduction is a medium through which genetic variation increases, it is not a requirement for natural selection to occur (i.e. an antibiotic-resistant strain of bacteria survives despite administration of antibiotics then reproduces via binary fission, increasing the proportion of bacteria in a population who contain the antibiotic resistance genes). Similarly, while both interspecies and intraspecies competition for resources such as food, water, and space may drive natural selection, these processes are not required for it to occur.
There was once a population on planet M311, called the Freg, who lived on a planet not unlike Earth. At the height of the Fregs technology and evolution, a collection of asteroids bombarded the planet and the devastation was so great that the planet was split in two, as was the Freg population. Much of the Freg population died, but many still survived on both pieces of M311.
The asteroid was an enormous catastrophe that drastically reduced the Freg population. As a result, their gene pool will be significantly smaller. What is this phenomenon called?
The Bottleneck Effect
The Darwin Conundrum
The Dinosaur Hypothesis
Radical Genetecism
The Extinction Example
The bottleneck effect is the correct answer here. The effect is defined as a sharp reduction in a populations size due to an environmental effect. In this scenario, the asteroids were the environmental effect and it caused the Freg population to decrease significantly. Also, none of the other answers are real theories.
Which of the following is true of genetic drift?
Genetic drift involves the random change of allele frequencies in a population
The effects of genetic drift are negligible in smaller populations
Genetic drift only occurs in populations at Hardy-Weinberg equilibrium
Genetic drift helps reduce the frequency of harmful alleles in a population
None of these statements are true
Genetic drift is a direct result of independent assortment. Since genes are not inherited by any organized mechanism, there are random fluctuations during which certain alleles experience an increase in frequency over others.
Genetic drift results in random changes in allele frequency; these changes are not a cause of genetic drift. In smaller populations and extreme cases, random changes can result in the loss of an allele entirely within the population. The results of genetic drift are more prominent in smaller populations due to their already reduced gene pool. Since genetic drift is random, both beneficial and harmful alleles can be promoted or eliminated.
Genetic drift cannot increase genetic diversity. The only way to increase genetic diversity is by the introduction of new traits and alleles. Genetic drift can reduce genetic diversity by eliminating alleles from a population, but is incapable of creating new traits. This can only be done through mutation.
A massive pre-historic earthquake caused the separation of approximately 500 people from the rest of their much larger population by an impassible fissure in the Earth’s crust. Which of the following would be the LEAST helpful in understanding the immediate future of this sub-group during the next fifty years?
Natural selection
The founder effect
The bottleneck effect
Genetic drift
A smaller group being separated permanently from a larger population is a classic example of the founder effect. These 500 members likely have far less genetic diversity than the larger population, so the subsequent population that develops will only contain alleles found in these 500 members.
The founder effect is a particular example of the bottleneck effect, wherein the number of individuals in a population is reduced very quickly from a non-selective pressure, such as a natural disaster or geographic barrier. Though the rest of the larger population is presumably still alive, these 500 people have gone from living in a large population to living in a relatively small one. The result is a decrease in genetic diversity when the smaller portion of the population is compared to the previously-existing larger group.
In the immediate future, this group could experience genetic drift wherein the relative frequencies of their alleles shift due to random chance. Genetic drift is more prominent in smaller groups, and would therefore help to understand what could happen in the population's immediate future. Since the group is relatively small, we could expect to see the results of genetic drift as early as fifty years after the separation event.
Natural selection occurs over many generations and longer time periods. It would not help us to understand the immediate future of this new population.
When a population is reduced for a short period of time, and only rare alleles are lost, this is referred to as which of these?
Bottlenecking
Divergence
The Founder Effect
Natural selection
Genetic drift
When a population is reduced for a short period of time, only the rarest alleles are usually lost, as is seen in bottlenecking. In order for a significant change in allelic frequency to be seen, the population must become significantly small, and it must stay small for a significant amount of time. The latter is referred to as the Founder Effect.
A population of wolves is living in an area when a tornado strikes and kills most of the wolves. The population of the wolves has been greatly reduced. Which of the following best describes the impact of the disaster on the genetic makeup of the population of wolves?
Bottleneck effect
Founder effect
Gene flow
Hardy-Weinberg principle
Cannot be determined from the information
The Bottleneck effect happens when an event occurs that drastically reduces the population of a species. The remaining individuals most likely do not represent the genetics of the population before the catastrophic event, since it becomes a much smaller sample size.
A population of geese migrates from Canada to Florida every winter. Individuals from the Canadian population sometimes breed with native Floridian geese. What is this an example of?
Gene flow
Genetic drift
Sympatric speciation
A prezygotic barrier
This is an example of gene flow, because a small number of individuals from one population are passing some genes on to those in another population. Genetic drift occurs within a single population, so it does not apply here. This is not an example of speciation. There can't be a prezygotic barrier present if the geese are able to successfully mate.
Which type of isolation between populations is due to barriers related to time, such as differences in mating periods or differences in the time of day that individuals are most active.
Temporal isolation
Geographic isolation
Reproductive isolation
Two of these
Behavioral isolation
Temporal isolation is between populations due to barriers related to time, such as differences in mating periods or differences in the time of day that individuals are most active. Geographic isolation between populations is due to physical barriers, not time. It wouldn't be both of them because only temporal isolation deals with time, versus geographic isolation is based on the physical barrier between populations such as mountains, rivers, or, for example, insects living on different trees in the jungle. Reproductive isolation is the inability to interbreed between species for various reasons like sterile offspring, physical incompatibility, or different mating rituals.
Select the best example of the bottleneck effect.
Drought causes a local lake to shrink drastically. Eagles catch and eat nearly all the fish before seasonal rains replenish the level of the lake. The fish population eventually returns to its original numbers.
A pair of wolves (1 male and 1 female) are released into a large national park to reduce the population of deer. The wolves prosper in their new prey-rich environment and eventually establish a larger wolf population.
A fungus nearly wipes out all of a farmer's pea plants. Later the farmer learns from a botanist that the survivors possessed a gene that made those pea plants grow a thicker cuticle causing the fungus to be unable to take hold and kill the plant.
During a flash flood a small group of fish inhabiting a river are able to swim through the flood waters to a nearby lake where they remain when the waters subside. This group of fish eventually dominates the lake which previously was home to smaller fish.
None of these
The bottleneck effect occurs when a random and catastrophic event reduces the population of an organism by a large number. The remaining individuals repopulate the area after the event, but the genetic diversity of the population is greatly reduced. The founder effect occurs when a group of individuals are separated from the main population and subsequently establish a new population. This new population's genetic diversity is also greatly reduced. In both cases a small number of individual establish a population and this small "pool" of genes is how genetic diversity is reduced. The wolves are separated from their pack by being released in a new area and then established a new population; this is an example of the founder effect. The pea plants were killed by a random event, but the survivors did not survive by random chance. Instead they had a gene that gave them higher fitness compared to the other members. This is a better example of natural selection. The fish in the flash flood were separated from the main population and subsequently established a new population in the nearby lake. This is an example of the founder effect. The drought lake is the best example of the Bottleneck effect because the event was random and the survivors lived due to random chance. A small number of the fish reestablished their population in the lake, their genetic diversity was also reduced.
What is the founder effect?
Loss of genetic variety due to a small number of individuals from a larger population establishing a new population
The evolution of a new species
Introduction of a new species that has a higher fitness than the native populations
A decrease in genetic variety due to fluctuation in numbers of specific traits in a population
The founder effect describes the phenomenon when a smaller group that originally came from a part of a larger population forms their own population. This new population will likely have a biased gene pool that will not be identical to the parent population. For example, if a certain species of bird gains a mutation such that some members are capable of flying farther, these birds may eventually separate to a different location and form their own unique population with a higher predominance of the "sustained flight" mutation than the original population.
The founder effect, after a long time, can lead to speciation, but this is not an essential part of the founder effect. Introducing a new species to native populations may influence the balance of the ecosystem and change genetic frequencies, but is not linked to the founder effect. A decrease in genetic variety due to fluctuation of certain traits would more aptly describe the bottleneck effect.