AP Biology : Understanding Hardy-Weinberg Assumptions and Calculations

Study concepts, example questions & explanations for AP Biology

Example Questions

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Example Question #1 : Understanding Hardy Weinberg Assumptions And Calculations

Which of the following is NOT an assumption required for Hardy-Weinberg equilibrium?

Possible Answers:

No mutations

No selection is occurring

Population size must fluctuate

Random mating

No migration

Correct answer:

Population size must fluctuate

Explanation:

Hardy-Weinberg states that for a population to be in equilibrium, it must not be experiencing migration, genetic drift, mutation, or selection. By this definition, population size cannot fluctuate.

Example Question #2 : Understanding Hardy Weinberg Assumptions And Calculations

According to Hardy-Weinberg calculations, a population's allele frequency will remain the same from generation to generation as long as evolution is not occurring. There are five conditions that must be met for equilibrium to remain in effect in a population.

Which of the following is not a condition for Hardy-Weinberg equilibrium to remain in effect?

Possible Answers:

The population must be large

No gene flow may occur

No selection may occur

Nonrandom mating must occur

No mutations may occur

Correct answer:

Nonrandom mating must occur

Explanation:

Random mating must occur in the population in order for the equilibrium to remain. If nonrandom mating occurred, allele frequency in the population would change. The alleles frequency of those mating the most would increase, while that of those mating less would decrease.

Large populations must be used to minimize the effects of genetic drift. Mustations cannot occur, as these could introduce new alleles.

It is important to note that no natural populations exist in Hardy-Weinberg equilibrium. This is simply a theoretical tool.

Example Question #3 : Understanding Hardy Weinberg Assumptions And Calculations

Imagine that a population is in Hardy-Weinberg equilibrium. A certain gene presents as two different alleles, and 49% of the population is homozygous dominant.

What percentage of the population is homozygous recessive?

Possible Answers:

42%

Further information is needed to solve the problem

9%

51%

Correct answer:

9%

Explanation:

When a population is in Hardy-Weinberg equilibrium, we can quantitatively determine how the alleles are distributed in the population. Pis equal to the proprtion of the population that is homozygous dominant based on the equation p+ 2pq + q2 = 1. We also know that p + q = 1.

Since P= 0.49 in this case, we know that p is equal to 0.7. Since there are only two alleles for this gene, we know that the other allele, q in this case, is 0.3. Since homozygous recessive is referred to as q2 in the equation, we can plug in the value of 0.3 and determine that q2 = 0.09. As a result, we confirm that 9% of the population is homozygous recessive.

Example Question #4 : Understanding Hardy Weinberg Assumptions And Calculations

If four percent of the population is homozygous recessive for the trait that carries dimples (recessive), what is the fractional frequency of the dominant allele?

Possible Answers:

0.8

0.2

0.16

0.64

Correct answer:

0.8

Explanation:

Using the Hardy-Weinberg law to solve for allele frequency in populations, you can solve for the answer using the following two equations.

p is the fractional frequency of the dominant allele, q is the fractional frequency of the recessive allele, and q2 is the fraction of the population that is homozygous recessive. q2 is given in the question to be 0.04 (or 4%).

Example Question #5 : Understanding Hardy Weinberg Assumptions And Calculations

In a population of fruit flies, the allele for red eyes is dominant to the allele for white eyes. If 50% the population is heterozygous and 25% is homozygous for white eyes, what is the frequency of the allele for red eyes?

Possible Answers:

Correct answer:

Explanation:

We must remember our two equations for allele frequency, according to Hardy-Weinberg equilibrium.

We know that, in the first equation, each term represents a total percentage of homozygotes or heterozygotes.  represents the allele for red eyes and  represents white.

Using the information from the question, we can solve for and .

The frequency of each allele is 0.50.

Example Question #6 : Understanding Hardy Weinberg Assumptions And Calculations

The allele frequencies for a population displaying Hardy-Weinberg equilibrium were found to be  dominant and recessive. What percentage of the population is homozygous dominant?

Possible Answers:

Correct answer:

Explanation:

For this question we are going to need to make use of the Hardy-Weinberg equilibrium equations. The equation we need to use is:

These numbers represent the percentages of each genotype found in a given population. We were given the values of  and  in the question.

After plugging the numbers into the equation, we can find the value of . This value will give us the frequency of homozygous dominant individuals.

Example Question #7 : Understanding Hardy Weinberg Assumptions And Calculations

Eye color in a certain species is decided by a single gene locus. Only two alleles influence eye color in a population of this species that exists in Hardy-Weinberg equilibrium. The dominant allele codes for brown eyes, while the recessive allele codes for blue eyes.

If the frequency of the brown allele is , what percent of the population is heterozygous at this locus?

Possible Answers:

Correct answer:

Explanation:

For problems of this type, we need to understand the Hardy-Weinberg equations:

Here,  represents the frequency of the dominant allele, while c refers to the frequency of the recessive allele.  and  denote the proportion of homozygous dominant and recessive phenotypes, respectively. Finally, the proportion of heterozygotes is denoted by .

We already know that , and if only two alleles are present in the population,  must be equal to .

Using the values for and , we can solve for the proportion of heterozygotes using the term of the Hardy-Weinberg equation.

Example Question #8 : Understanding Hardy Weinberg Assumptions And Calculations

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. There are sixteen homozygous dominant, forty-eight heterozygous, and thirty-six homozygous recessive snails. 

What are the allele frequencies for this population?

Possible Answers:

Correct answer:

Explanation:

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

In the second equation, corresponds to the frequency of homozygous dominant individuals, corresponds to the heterozygous frequency, and corresponds to the frequency of homozygous recessive individuals. We are given enough information to find each of these values from the question.

We can find the values of and by taking the square root of their squares.

Example Question #9 : Understanding Hardy Weinberg Assumptions And Calculations

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 #10 : Understanding Hardy Weinberg Assumptions And Calculations

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, .

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