AP Biology : Evolution and Genetics

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #3 : Population Genetics

A population of snails is in Hardy-Weinberg equilibrium. The snails come in two different colors: red, the dominant phenotype, and white, the recessive phenotype. The population consists of sixty-four red snails and thirty-six white snails.

Assuming that the population is in Hardy-Weinberg equilibrium, what is the value of ?

Possible Answers:

Correct answer:

Explanation:

We can solve this question using the Hardy-Weinberg equations:

is equal to the recessive allele frequency, while in the second Hardy-Weinberg equation corresponds to the frequency of the recessive phenotype.

The question tells us the number of dominant red snails and the number of recessive white snails. Using these values, we can find the frequency of the recessive phenotype.

From here, take the square root to find the value of .

Example Question #1 : Population Genetics

A population of snails is originally in Hardy-Weinberg equilibrium. The snails come in two different colors: red, the dominant phenotype, and white, the recessive phenotype. The original population has a dominant allele frequency of  and a recessive allele frequency of . A new predator is introduced to the habitat that is particularly fond of the red snails. After a few years the dominant allele frequency has been reduced to .

 What is the recessive allele frequency after the introduction of this predator?

Possible Answers:

Correct answer:

Explanation:

Most of the information in the question is actually superfluous because we are given the final dominant allele frequency. The dominant allele frequency corresponds to the variable in the Hardy-Weinberg equations.

The question tells us that the dominant allele frequency after introduction of the predator is . Use this value in the first Hardy-Weinberg equation to solve for the recessive allele frequency, .

Example Question #1634 : Ap Biology

A population is in Hardy-Weinberg equilibrium. In the population, 1% of individuals show the recessive trait for blue eyes. What is the value of  in this situation?

Possible Answers:

Correct answer:

Explanation:

For a population in Hardy-Weinberg equilibrium, every trait follows the equations:

In these formulas,  represents the frequency of the dominant allele and  represents the frequency of the recessive allele.  represents the frequency of the homozygous dominant genotype,  represents the frequency of the heterozygous genotype, and  represents the frequency of the homozygous recessive genotype.

In this case, the individuals with blue eyes would be represented by the homozygous recessive genotype. Using this data, we can solve for the frequency of the recessive allele.

Use the frequency of the recessive allele to find the frequency of the dominant allele, .

Example Question #1 : Population Genetics

A population of beetles exists in which black coloration is dominant to white. If there are 64 black beetles in the population, what is the dominant allele frequency?

Possible Answers:

More information is required to solve

Correct answer:

More information is required to solve

Explanation:

It is impossible to determine the allele frequency from the given information.

The problem only tells the number of black beetles, but does not give any information that would allow us to find the total number of beetles in the population. We do not have the homozygous recessive population or the distribution of heterozygotes and homozygous dominant beetles. Given information on the number of white beetles would allow us to calculate the recessive allele frequency, and subsequently the dominant allele frequency.

Example Question #11 : Understanding Hardy Weinberg Assumptions And Calculations

Which of the following is a Hardy-Weinberg assumption?

Possible Answers:

High rate of mutation

Gene flow between populations

Natural selection is in operation 

Random mating

Correct answer:

Random mating

Explanation:

Random mating is one of the five Hardy-Weinberg assumptions that help maintain equilibrium. If random mating occurs, in tandem with the other assumptions, we can reasonably assume that there will not be a shift in allele frequencies or distributions.

The other Hardy-Weinberg assumptions are that natural selection does not occur, mutation does not occur, genetic drift (gene flow) does not occur, and that the population size is large.

Example Question #11 : Understanding Hardy Weinberg Assumptions And Calculations

Which of the following is not a Hardy-Weinberg assumption?

Possible Answers:

Random mating occurs

Mutation frequencies are high

The population is large

Natural selection is not in operation

Correct answer:

Mutation frequencies are high

Explanation:

One of the five main assumptions is that mutations are negligible. This makes sense because, if a population is in Hardy-Weinberg equilibrium, evolution is not occurring. A low rate of mutations would help keep a population in equilibrium.

The five assumptions of Hardy-Weinberg equilibrium are a large population size, no natural selection, no mutation rate, no genetic drift, and random mating.

Example Question #11 : Population Genetics

A population is in Hardy-Weinberg equilibrium. The gene of interest has two alleles, with 16% of the population portraying the features of the recessive phenotype. What percentage of the population is heterozygous?

Possible Answers:

Correct answer:

Explanation:

Using the Hardy-Weinberg equilibrium equations, you can determine the answer.

The value of gives us the frequency of the dominant allele, while the value of gives us the frequency of the recessive allele. The second equation corresponds to genotypes. is the homozygous dominant frequency, is the heterozygous frequency, and is the homozygous recessive frequency.

16% of the population shows the recessive phenotype, and therefore must carry the homozygous recessive genotype. We can use this information to solve for the recessive allele frequency.

We can use the value of and the first Hardy-Weinberg equation to solve for .

Knowing both  and , you can use the second equation to find the percent of heterozygous organisms in the population.

Example Question #12 : Understanding Hardy Weinberg Assumptions And Calculations

A variety of grapes possesses a gene that generally determines the size of fruit produced. In a population of 200 plants, 194 show the dominant phenotype.

Based on the Hardy-Weinberg principles, what is the expected frequency of the dominant allele in this population?

Possible Answers:

Correct answer:

Explanation:

The Hardy-Weinberg equations can be used to determine the expected frequency of genes and genotypes within a population, provided that only Mendelian segregation and recombination of alleles are at work. This is calculated mathematically using the equations:

We are told that 194 plants in a population of 200 demonstrate the dominant phenotype. This means that the sum of the homozygous dominant and heterozygous individuals is represented by the 194 plants described.

So, 97% of the plants show the dominant phenotype. This means that 3% must show the recessive phenotype.

Using this, we can find the frequency of the recessive allele, , and subsequently the dominant allele, .

Example Question #11 : Understanding Hardy Weinberg Assumptions And Calculations

A person carrying two recessive alleles of a specific gene has a greater likelihood of developing lung cancer. The frequency of the dominant allele in a population is eighty-seven percent.

Based on the Hardy-Weinberg principle, what is the expected frequency of homozygous recessive genotype in this population?

Possible Answers:

Correct answer:

Explanation:

The Hardy-Weinberg equations can be used to determine the expected frequency of genes and genotypes within a population, provided that only Mendelian segregation and recombination of alleles are at work. This is calculated mathematically using the equations:

Let's start with what we know and how it relates to these equations. We are told that the dominant allele frequency () is 87%, and then asked to find the frequency of homozygous recessive individuals ().

Known:

Unknown:

Use the second Hardy-Weinberg equation to solve for .

Square this value for find the frequency of homozygous individuals.

Example Question #13 : Population Genetics

Hearing loss is caused by the inheritance of different genetic alleles: GM and GJ. The expected frequency of a GM allele is 90% in a given population.  

Based on the Hardy-Weinberg principle, what is the expected frequency of genotype GMGJ in the next generation of this population?

Possible Answers:

Correct answer:

Explanation:

The Hardy-Weinberg equations can be used to determine the expected frequency of genes and genotypes within a population, provided that only Mendelian segregation and recombination of alleles are at work. This is calculated mathematically using the equations:

In this example, the expected frequency to be solved for is the heterozygote GMGJ that is represented by the  component of the equation. We are told the frequency of the GM allele in the population, allowing us to solve for the frequency of the GJ allele. It is not necessary to know which allele is dominant and which is recessive in this particular question since we are dealing only with genotypes (phenotype is irrelevant).

Using these values, we can calculate the value of .

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