SAT II Biology E : Population Genetics and Hardy-Weinberg

Study concepts, example questions & explanations for SAT II Biology E

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Example Questions

Example Question #1 : Population Genetics And Hardy Weinberg

A population of dingos finds a new habitat to exploit due to the disappearance of one of their natural predators. They reproduce sexually and at random. Their population is supplemented by dingos from other packs entering their pack. They are able to hunt multiple species and have plenty of food. They are healthy and free of diseases. How do we know the assumptions for the Hardy-Weinberg equilibrium have been violated?

Possible Answers:

They are free of disease

Sexual reproduction is not occurring 

Other dingos are migrating to the population

The population size is not infinitely large

This organism is not diploid 

Correct answer:

Other dingos are migrating to the population

Explanation:

If other dingos are supplementing the population, we know that migration is occurring. Migration cannot occur if a population is to satisfy the conditions of Hardy-Weinberg equilibrium. 

Example Question #2 : Population Genetics And Hardy Weinberg

Which of the following conditions is not required to be true for a population in Hardy-Weinberg equilibrium?

Possible Answers:

Large population

No immigration or emmigration

No natural selection

Random mating

Random mutations

Correct answer:

Random mutations

Explanation:

The Hardy-Weinberg principle asserts that allele frequencies in a population remain constant; for example, if 50% of people have blue eyes, then each successive generation will continue to have 50% of people with blue eyes as long as certain assumptions are met. The Hardy-Weinberg equilibrium assumes that within a population random mating occurs, no migration occurs, no mutations occur, no natural selection occurs, and the population is sufficiently large. If any of these assumptions are not met, the allele frequencies of the population will change, causing the population to evolve. For this question, all of the answer choices except "Random mutations" (remember there must be no mutations) are required assumptions for the Hardy-Weinberg equilibrium to be in effect.

Example Question #3 : Population Genetics And Hardy Weinberg

A certain herd of horses contains black horses and brown horses. These horses are diploid organisms, and coat color is an autosomal trait. The gene for a brown coat (B) is completely dominant, while the gene for a black coat (b) is recessive. Assume that the population is in Hardy-Weinberg Equilibrium.

If prevalence of the R allele in the herd of horses is 0.6, what is the prevalence of black horses in the herd?

Possible Answers:

0.4

0.36

0.18

0.8

0.16

Correct answer:

0.16

Explanation:

This is a Hardy-Weinberg Equilibrium problem. The question stem gives you the prevalence of the dominant allele, 0.6. The prevalence of the dominant allele and the prevalence of the recessive allele must always add together to equal 1:

So, the prevalence of the recessive allele must be 0.4:

The prevalence of the recessive phenotype is equal to the prevalence of the recessive allele squared:

In this case, black coat color is a recessive trait, so the prevalence of this recessive phenotype is equal to the prevalence of the recessive allele squared, or 0.16.

Example Question #4 : Population Genetics And Hardy Weinberg

A given trait has two alleles. It is inherited in a completely autosomal dominance pattern in a diploid population. Which of the following is NOT true if this population is in Hardy-Weinberg equilibrium? 

Possible Answers:

Allele frequencies vary significantly from generation to generation.

The frequency of the dominant allele plus the frequency of the recessive allele must add up to 1.

The frequency of the recessive phenotype is equal to the frequency of the recessive allele squared.

The frequency of the dominant phenotype is equal to the frequency of the dominant allele squared.

The frequency of the heterozygous genotype is equal to two times the frequency of the dominant allele times the frequency of the recessive allele.

Correct answer:

Allele frequencies vary significantly from generation to generation.

Explanation:

Let's say that the frequency of the dominant allele ("A") is represented by p, and the frequency of the recessive allele ("a") is represented by q. Since these are the only two alleles for the trait, their frequencies must add up to one:

The frequency of the AA genotype is , the frequency of the Aa genotype is , and the frequency of the aa genotype is .

Hardy-Weinberg equilibrium assumes the absence of external forces like genetic drift and selective pressure. In other words, it is based on the assumption that allele frequency is relatively constant across generations.

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