AP Biology : Understanding Types of Selection

Study concepts, example questions & explanations for AP Biology

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Example Questions

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Example Question #232 : Evolution And Genetics

Which of the following statements reflecting Darwin's theory of evolution is false?

Possible Answers:

Genetic variations can be inherited

All answer choices reflect correct statements about Darwin's theory of evolution

Accumulation of adaptations leads to speciation

Members of a population produce more offspring than the environment can support

Correct answer:

All answer choices reflect correct statements about Darwin's theory of evolution

Explanation:

Darwin's Theory of Evolution can be described by the following statements.

1) Individuals of any population vary from one another in many characteristics, due to mutation.

2) Genetic variations can be inherited.

3) Members of a population produce more offspring than the environment can support, leading to competition for resources

4) Those individuals whose inherited characteristics fit them best to their environment are likely to leave more offspring than less fit individuals.

5) Over generations of natural selection, favorable adaptations are perpetuated in a species. Accumulation of these favorable changes eventually results in speciation.

Example Question #1 : Natural Selection

Charles Darwin described four key observations pertaining to natural selection from his voyage around the world. Which of the following is NOT one of Darwin’s observations of nature?

Possible Answers:

All species are capable of producing more offspring than their environment can support

Traits are inherited from parents to offspring

Members of a population often vary greatly in their traits

Individuals of a population evolve through interaction with their environment

Correct answer:

Individuals of a population evolve through interaction with their environment

Explanation:

During his travels, Darwin essentially developed the fundamental principles of evolution. Included in these observations were that traits are inherited from parent to offspring, members of a population exhibit genetic diversity (numerous traits), and that organisms are capable of producing more offspring than the environment can support. The fourth observation was that, owing to a lack of food or other resources, many offspring do not survive. Together, these observations helped shape Darwin's theories of natural selection and biological fitness to explain the trends that he had seen.

A key point about natural selection is that it is the population that evolves over time, not individual members of a population lifetime. Individuals that may have inherited advantageous traits are likely to produce more offspring than other members of the population, which drives natural selection within the context of the environment. Environmental pressures can affect the forces of natural selection, but cannot directly result in the production of new traits or the inheritance of those traits.

Example Question #1 : Understanding Types Of Selection

Darwin described his theory of natural selection as which of the following?

Possible Answers:

Survival of the fittest

Inheritance of acquired characteristics

Punctuated equilibrium

Descent with modification

Correct answer:

Descent with modification

Explanation:

Darwin described his theory as "descent with modification," meaning that offspring inherit their genetic material from their parents, but with slight modifications. Darwin proposed that those slight modifications which provided a fitness benefit (made it more likely that an organism would reproduce) were more likely to be passed on.

Example Question #1 : Understanding Types Of Selection

Charles Darwin's voyage to the Galapagos islands and study of the beak shape of finches was integral to his research and subsequent ideas about __________ through __________

Possible Answers:

natural selection . . . evolution

evolution . . . natural selection

temporal isolation . . . predator-prey relationships

phenotypic degradation . . . selection pressures

sympatric speciation . . . evolution

Correct answer:

evolution . . . natural selection

Explanation:

Charles Darwin studied finches in the Galapagos, which prompted his work on natural selection. This was observed as only the finches who were evolutionarily prepared reproduced, thus increasing their traits in the gene pool 

Example Question #1 : Understanding Types Of Selection

Why do biologists not normally distinguish between micro- and macro- evolution?

Possible Answers:

The line between "micro" and "macro" is mostly arbitrary and depends on the individual's definition.

They are differences between population change and speciation, and the term "species" is impossible to define.

"Micro" vs. "Macro" evolution is an outdated principle of Lamarckian evolution.

The terms "micro" and "macro" do not apply to the biological process.

"Micro" and "macro" are terms only used to try to disprove evolutionary theory.

Correct answer:

The line between "micro" and "macro" is mostly arbitrary and depends on the individual's definition.

Explanation:

Both "microevolution" and "macroevolution" are driven by the same biological process: natural selection. While the former refers to change within species and the latter refers to change to a new species, the line between what constitutes a species change is difficult to define. Since both terms refer to the same process of natural selection, the term evolution applies to both, whether as a single adaptation or a series of adaptations that culminate into a single species.

Example Question #5 : Understanding Darwin

What aspect of the environment did Darwin hypothesize had caused the Galapagos mockingbirds to differentiate into four different species?

Possible Answers:

Because each species had a different food source, each parent bird acquired advantageous changes during its lifetime for accessing that food source, which it passed onto its offspring.

Each bird species had been created separately from the other, with little variation over time.

What Darwin had mistaken to be new species were actually the same species with slight colorations depending on the environment.

None of these

Each species was found on a different island. Because the populations were separated from each other, they acquired different changes from each other over time.

Correct answer:

Each species was found on a different island. Because the populations were separated from each other, they acquired different changes from each other over time.

Explanation:

Speciation occurs when two populations are separated from each other and accumulate different changes due to different environments. When the birds migrated to the Galapagos and made homes on each island, they became physically different from each other over time. This was one observation to the theory of natural selection.

Example Question #2 : Understanding Types Of Selection

Which of the following is most affected by natural selection?

Possible Answers:

Merlot grapes

Poodles

Angora rabbits

Influenza

Correct answer:

Influenza

Explanation:

Influenza (the flu virus) is a real-life example of natural selection that is most evident during an annual time period when the influenza virus infection peaks. The repeated or cyclical nature of flu outbreaks is caused by the natural selection of the virus for traits that allow it to evade the immune system and replicate, a process that actually results in new distinct strains of influenza virus.

In contrast, the other answers are all examples of artificial selection by which the specific variety or breed has been purposely selected for specific traits. Poodles and Angora rabbits have been purposely bred by humans to select for traits that affect their fur. Merlot wine is produced from a certain strain of grapes that have been bred for their taste. Note that artificial selection differs from genetic modification, as no new traits have been introduced to these strains.

Example Question #1 : Natural Selection

A population of giraffes lives in a forest with trees of varying heights. Following a flood in the area, all shorter plants were destroyed and only tall trees remain. After many generations, it is noted that giraffes living in this forest have longer necks, on average, than giraffes living in the same forest prior to the flood. 

What type of selection has occurred?

Possible Answers:

Disruptive selection

Destabilizing selection

Directional selection

Extreme selection

Stabilizing selection

Correct answer:

Directional selection

Explanation:

Directional selection is natural selection that favors a phenotype at an "extreme" for a particular trait. In this example, we are looking at the height trait. Individuals with taller phenotypes exhibit greater fitness due to their ability to reach the food source more easily. The new environment favors taller giraffes, and thus, after many generations, the phenotype of the population as a whole will be skewed towards the tall end of the height spectrum.

Stabilizing selection favors the average phenotype for a given trait. Disruptive selection favors both extremes of a phenotype, but favors against the average.

Example Question #1 : Natural Selection

White mice are homozygous for a recessive pigmentation trait. Brown mice are homozygous dominant for the same pigmentation trait, and beige mice are heterozygous for the trait. In a particular ecosystem, natural selection favors the beige mice because they blend in with the brush and leaves. What concept explains to this type of selection? 

Possible Answers:

Heterozygote advantage

Balancing selection

Frequency-dependent selection

Directional selection

Founder effect

Correct answer:

Heterozygote advantage

Explanation:

Heterozygote advantage occurs when heterozygotes at a particular locus, such as pigmentation, have greater fitness than do both kinds of homozygotes. If the heterozygote favors an intermediate phenotype, such as beige mice, it is also stabilizing selection. Frequency-dependent selection occurs when the fitness of a phenotype depends on how common it is in the population. Together, heterozygote advantage and frequency-dependent selection lead to a balancing system. The founder effect occurs when a few individuals of a population become isolated and form a new population whose gene pool differs from the original population. Directional selection occurs when conditions favor individuals at one extreme of a phenotypic range, thereby shifting a population’s frequency curve for the phenotypic character in one direction or another.

Example Question #1 : Understanding Types Of Selection

Which of the following best describes the impact of purifying selection?

Possible Answers:

It increases genetic diversity

It removes variation from the population

It increases frequency of an allele

It is the same as disruptive selection 

Correct answer:

It removes variation from the population

Explanation:

Purifying selection is a type of natural selection impacts genetic diversity. Purifying selection removes variation from a population, meaning that there is a decrease in genetic diversity.

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