AP Biology : Understanding Genetic Drift, Bottleneck Effect, and Founder Effect

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #31 : Population Genetics

Which scenario best describes genetic drift?

Possible Answers:

None of these

Two populations of fish are separated by a strip of land that divides the lake into two bodies of water. For all practical purposes each side of the like is identical except the females on one side only mate with males with a certain coloration. Over time the populations become quite different.

Two populations of fish are separated by a strip of land that divides the lake into two bodies of water. For all practical purposes each side of the like is identical except there are different predators on either side. Over time the populations become quite different.

Two populations of fish are separated by a strip of land that divides the lake into two bodies of water. For all practical purposes each side of the like is identical except the sources of food. Over time the populations become quite different.

Two populations of fish are separated by a strip of land that divides the lake into two bodies of water. For all practical purposes each side of the like is identical; the selective pressures are identical. Over time the populations become quite different.

Correct answer:

Two populations of fish are separated by a strip of land that divides the lake into two bodies of water. For all practical purposes each side of the like is identical; the selective pressures are identical. Over time the populations become quite different.

Explanation:

Genetic drift is a change in allele frequencies in a population through random chance. It occurs over time and isn't a result of more fit organisms passing on their genes. In all but one of the answer choices there is some selective pressure that causes a change in the population that is not related to random chance. Thus, the example with the exact same selective pressures is the only scenario that could result in genetic drift. Predation can cause one allele to die out and another to prosper if one allele causes the organism to be better camouflaged. If individuals in a population have a preference for one type of allele then that allele will prosper. Sources of food can also cause an organism to change. For instance, if on one side of the lake the dominant food source is algae and on the other side smaller, quicker fish are the source of food, then over time the fish on either side of the hypothetical lake could diverge. One gaining a better ability to scoop algae and the other becoming very agile.

Example Question #41 : Population Genetics

Select the best example of the bottleneck effect.

Possible Answers:

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

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. 

Correct answer:

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.

Explanation:

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.

Example Question #41 : Population Genetics

Which of the following is true regarding genetic drift?

Possible Answers:

Genetic drift reduces genetic variation

All of these

It is the change in allele frequency due to sampling error

Effect of genetic drift is less in larger populations

Correct answer:

All of these

Explanation:

Genetic drift is a change in allele frequency between generations due to sampling error. Since genetic drift makes certain allele variations disappear, it decreases genetic variation. Additionally, genetic drift has a smaller effect in larger populations and a large effect in small populations.

Example Question #11 : Understanding Genetic Drift, Bottleneck Effect, And Founder Effect

Which of the following is an example of gene flow?

Possible Answers:

Horizontal gene transfer

Both migration and horizontal gene transfer

Migration

Neither migration nor horizontal gene transfer

Correct answer:

Both migration and horizontal gene transfer

Explanation:

Gene flow is a mechanism of evolution in which genes are transferred between populations. Two examples of gene flow are migration and horizontal gene transfer. In the case of migration, the movement of individuals into or out of a population also results in a transfer of alleles. Horizontal gene transfer (common in bacteria) is the transfer of genes through means other than reproduction (i.e. plasmid exchange).

Example Question #1821 : Ap Biology

Evolution that occurs within a population due to the production of a finite number of zygotes from a given gene pool is referred to as which of these?

Possible Answers:

Genetic drift

Inbreeding depression

The Fonder Effect

Natural selection

Loss of heterozygosity

Correct answer:

Genetic drift

Explanation:

Genetic drift is due to the production of a finite number of zygotes within a population. This causes allele frequencies to change from one generation to the next. Genetic drift can result in the reduction of the fitness of individuals within a population if the alleles passed on are deleterious.

Example Question #1822 : Ap Biology

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?

Possible Answers:

The Founder Effect

Bottlenecking

Genetic drift

Natural selection

Divergence

Correct answer:

Bottlenecking

Explanation:

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.

Example Question #12 : Understanding Genetic Drift, Bottleneck Effect, And Founder Effect

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?

Possible Answers:

Gene flow

A prezygotic barrier

Genetic drift

Sympatric speciation

Correct answer:

Gene flow

Explanation:

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.

Example Question #1821 : Ap Biology

For natural selection to occur, which of the following must be true of a population?

Possible Answers:

The population must be isolated

Must be capable of sexual reproduction

Having many populations in one area

Food is not available

Phenotypic variations must be based on genetic variations 

Correct answer:

Phenotypic variations must be based on genetic variations 

Explanation:
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. 

Example Question #13 : Understanding Genetic Drift, Bottleneck Effect, And Founder Effect

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.

Possible Answers:

Geographic isolation

Behavioral isolation

Two of these

Temporal isolation

Reproductive isolation

Correct answer:

Temporal isolation

Explanation:

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.

Example Question #12 : Understanding Genetic Drift, Bottleneck Effect, And Founder Effect

Which of the following is an example of genetic drift?

Possible Answers:

A massive storm randomly kills many individuals in a population, changing the frequency of alleles in that population.

An allele increases in frequency due to the increase in fitness it provides the organism.

Individuals from one population move and mate with members of a different population.

An organism is born with traits not attributed to the alleles of its parents, but a brand new allele.

All of these are examples of genetic drift.

Correct answer:

A massive storm randomly kills many individuals in a population, changing the frequency of alleles in that population.

Explanation:

Genetic drift occurs when the frequency of alleles in a population change by random chance. Change in allele frequency based on biological fitness is natural selection, not genetic drift. The change in allele frequency due to members moving from one population to another describes migration. A brand new allele that did not exist in the parents is the result of mutation.

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