AP Biology : Evolution and Genetics

Study concepts, example questions & explanations for AP Biology

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Example Questions

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

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

Possible Answers:

Food is not available

Having many populations in one area

The population must be isolated

Must be capable of sexual reproduction

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 #12 : 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

Two of these

Reproductive isolation

Behavioral isolation

Temporal 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 #13 : Understanding Genetic Drift, Bottleneck Effect, And Founder Effect

Which of the following is an example of genetic drift?

Possible Answers:

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

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

All of these are examples of genetic drift.

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

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

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.

Example Question #44 : Population Genetics

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?

Possible Answers:

Cannot be determined from the information

Gene flow

Hardy-Weinberg principle

Bottleneck effect

Founder effect

Correct answer:

Bottleneck effect

Explanation:

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. 

Example Question #21 : Understanding Genetic Drift, Bottleneck Effect, And Founder Effect

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?

Possible Answers:

The Extinction Example

The Bottleneck Effect

Radical Genetecism

The Dinosaur Hypothesis

The Darwin Conundrum

Correct answer:

The Bottleneck Effect

Explanation:

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.

Example Question #241 : Evolution And Genetics

Which of the following is true of genetic drift?

Possible Answers:

None of these statements are true

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

Correct answer:

Genetic drift involves the random change of allele frequencies in a population

Explanation:

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.

Example Question #1 : Perform Chi Squared Test

In a population of flowers, red is dominant to white. A true-breeding white flower is crossed with a heterozygous flower. Determine the expected ratios of this cross. Given observed values: 63 white flowers, 37 red flowers, determine:

1) The chi squared value

2) The degrees of freedom

3) The p-value

Possible Answers:

1) 14.44    

2) 2    

3) p>0.005

1) 6.76    

2) 1    

3) p>0.025

1) 3.35    

2) 4    

3) p=0.25

1) 6.76    

2) 2    

3) p=0.05

Correct answer:

1) 6.76    

2) 1    

3) p>0.025

Explanation:

First, determine the expected ratios using a Punnet Square. Given that red is dominant to white, the genotype of a true-breeding white flower can be denoted rr, and the genotype of a heterozygous flower can be denoted Rr. This cross will produce 50% Rr, 50% rr. Then, converting these percentages to decimals (50%= 0.50), and multiplying by the total population size of the observed population (0.50*100), gives expected values of 50 Rr (red flowers) and 50 rr (white flowers). These expected values and the observed values can then be plugged into the chi square equation . The equation will be . Degrees of freedom is n-1, so 2-1= 1. To determine p-value, use critical values table. The chi square value of 6.76 with 1 degrees of freedom will fall between a critical value corresponding with a p-value of 0.05 and 0.025. Thus, p>0.025

Example Question #1 : Perform Chi Squared Test

In a chi squared test, the greater the difference between the observed and expected frequencies of a trait, the ___ the p-value.

Possible Answers:

more positive

more negative

greater

lower

Correct answer:

lower

Explanation:

 A larger difference between observed and expected values will result in a larger chi square value. Using the critical values table, for a given degrees of freedom, as chi square value increases, p-value decreases.

Example Question #1 : Perform Chi Squared Test

If the p-value determined by a chi-square test is low, which is possible

Possible Answers:

The null hypothesis is accepted

The alternative hypothesis is rejected

The null hypothesis is rejected

The chi square value is also low

Correct answer:

The null hypothesis is rejected

Explanation:

When the p-value is equal to or below the significance level (alpha), the null hypothesis is rejected. For the p-value to be low, the chi square value would need to be large (large difference between observed and expected values). The null hypothesis would not be accepted (under no circumstance is a null hypothesis “accepted”; onlay rejected or failed to reject). The alternative hypothesis would be accepted if the p-value is equal to or below the significance level (alpha).

Example Question #1 : Perform Chi Squared Test

Which of the following chi square values would likely result in rejection of the null hypothesis?

Possible Answers:

1.97

7.36

13.8

0.35

Correct answer:

13.8

Explanation:

A larger difference between observed and expected values will result in a larger chi square value. Using the critical values table, for a given degrees of freedom, as chi square value increases, p-value decreases. A small p-value results in rejection of the null hypothesis.

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