High School Biology : Understanding Natural Selection

Study concepts, example questions & explanations for High School Biology

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Example Questions

Example Question #1 : Understanding Natural Selection

Which of the following is not a result of natural selection?

Possible Answers:

Pesticide-resistant insects

Giraffes have long necks in order to feed from trees

Development of genetically modified organisms

Rat snakes have different coloration depending on their habitats

Correct answer:

Development of genetically modified organisms

Explanation:

Development of genetically modified organisms is an example of artificial selection due to human intervention. Desirable organisms are allowed to generate offspring, passing on the selected genes. Non-optimal organisms are prevented from creating offspring.

The other options are all evolutionary changes that occurred naturally. Snake coloration is a mechanism to avoid predators and stalk prey. A giraffe's neck facilitates accessibility to its food source. An insect that is resistant to a certain chemical will survive to create offspring.

Example Question #2 : Understanding Natural Selection

Which of the following is one of Charles Darwin’s theories about evolution and natural selection, known as descent with modification?

Possible Answers:

Changes to an organism occur rapidly, within a few generations

New species that appear in the fossil record are actually descendants of older species

The environment in which a species lives is unrelated to natural selection

Similar organisms arise in distant geographic locations 

Correct answer:

New species that appear in the fossil record are actually descendants of older species

Explanation:

As an example of decent with modification, Darwin observed different species of finches on the Galapagos Islands and thought that they had descended from a common ancestor. Individuals that have inherited advantageous traits are likely to produce more offspring than other members of the population, which drives natural selection. This occurs within a particular environment or geographic location. Decent with modification is essentially the theory of inherited mutations that can alter the gene pool of a population, eventually resulting in speciation.

Example Question #3 : Understanding Natural Selection

The theory that the most well-adapted individuals in one generation tend to be the ones that leave the most offspring is called __________.

Possible Answers:

natural selection

evolution

convergent evolution

adaptation

genetic drift

Correct answer:

natural selection

Explanation:

Natural selection is the unequal survival and reproduction of organisms resulting in the preservation of favorable adaptations. Natural selection favors individuals with higher biological fitness, which is defined by the individual's ability to produce viable offspring.

Convergent evolution is the independent evolution of similar structures among unrealted organisms as a result of similar environmental pressures. Evolution is any change in the proportions of different genotypes in a population from one generation to the next. Genetic drift is a change in the allele frequencies of a small population purely by chance. An adaptation is a characteristic of an organism that helps it survive and reproduce in a particular environment. 

Example Question #2 : Genetics And Evolution

Which of the following best describes Darwin's theory of natural selection?

Possible Answers:

Giraffes would never obtain neck lengths corresponding to leaf height because of ecological conditions

Giraffes would obtain neck lengths corresponding to leaf height over multiple generations

Giraffes would obtain neck lengths corresponding to leaf height if the appropiate alleles were newly introduced into the gene pool

Giraffes would obtain neck lengths corresponding to leaf height without selective pressures

Giraffes would obtain neck lengths corresponding to leaf height within a generation

Correct answer:

Giraffes would obtain neck lengths corresponding to leaf height over multiple generations

Explanation:

Natural selection is a theory that explains that organisms better adapted to their environment will have a higher likelihood of survival. In the case of the giraffes, the height at which giraffes found leaves is the selective pressure. Assuming that the population has variable neck length, those that had neck lengths better suited for the height at which the leaves were at had better survival. This meant that those with necks that were either too long or too short were unable to reach the leaves as effectively, resulting in less survival. Therefore, the populations phenotypic frequencies will shift, favoring optimal neck lengths. The idea that ideal neck length would be reached within one's lifespan is Lamarkian, and was disproven. 

Example Question #3 : Understanding Natural Selection

According to Darwin, the results of natural selection are best described by which of the following choices?

I. Unity of life

II. Diversity of life

III. Match between organism and their environment

IV. An organism's relative fitness

Possible Answers:

I, II, and IV

I, II, III, and IV

I, III, and IV

I, II, and III

II, III, and IV

Correct answer:

I, II, and III

Explanation:

While observing South America aboard the Beagle, Darwin noticed how well animals were suited for their environments.  He also noted that the animals on the Galapagos were quite similar to those on the mainland, although they had differences that helped them thrive in their different habitats.  Due to the unity/similarity and yet the diversity of life, Darwin hypothesized that animals from the mainland colonized the islands.  From a few species, many more developed and evolved to fill the niches of the island. 

Example Question #6 : Genetics And Evolution

Birds of the same species were blown from the mainland to a nearby island in a storm.  While living on the island, natural selection acts in favor of the birds with smaller beaks, as birds with large and medium sized beaks have a harder time gathering food.  This process is an example of which of the following choices?

Possible Answers:

Directional selection 

Disruptive selection

Relative fitness

Sexual selection

Stabilizing selection

Correct answer:

Directional selection 

Explanation:

Directional selection occurs when conditions favor individuals exhibiting one extreme of a phenotypic range.  In this example, conditions on the island favor the birds with small beaks, which alters the population’s frequency curve for the phenotypic character in one direction (towards smaller beaked individuals).  Disruptive selection would act in favor both large and small beaks (phenotypic extremes), while stabilizing selection would act against both extremes. In other words, stabilizing selection would act in favor of medium sized beaks or those that lie in the median of the phenotypic curve. 

Example Question #5 : Genetics And Evolution

Individuals of a particular species of ginger plants that are homoygous recessive for alleles of a gene that regulates height are phenotypically sickly and small. There are two population of ginger plants in this region: a population that grows near the river and another population that grows in the mountains. The river population has a high percentage of heterozygous individuals carrying the recessive allele, with some homozygotes that are sickly. Close to no individuals carry the recessive allele in the mountains. Considering how natural selection affects allele frequencies, what is a potential reason this recessive allele exists in the river population?

Possible Answers:

The homozygote recessive sickly plants can survive near the river but not the mountain

The river population of the ginger plant is older than the mountain population

The mountain area is a harder environment for the ginger to grow

Heterozygotes carrying one recessive allele and one dominant allele have a fitness advantage in the river area

Correct answer:

Heterozygotes carrying one recessive allele and one dominant allele have a fitness advantage in the river area

Explanation:

Maintaining a recessive allele that can cause a sickly phenotype when an individual is homozygous recessive does not seem advantangeous. However, if the recessive allele is maintained in one population over another, then it suggests that being heterozygous for this trait may produce a fitness benefit based on habitat.  As a result, it is not eliminated from the population. A similar example is sickle cell anemia in humans. In particular cases of sickle cell anemia, heterozygous individuals are protected from malaria while individuals that are homozygous have health problems. In other words, the fitness advantage associated with heterozygous carriers selects for maintining recessive alleles within the population.

Example Question #4 : Understanding Natural Selection

Several individuals in a population of green beetles acquire a mutation that makes them blue and toxic to their primary predatory bird species. What do you expect will happen to this population over time?

Possible Answers:

The poisonous ones have lower fitness, and natural selection will lead to the population of beetles to stay green

The poisonous ones have higher fitness, and stabilizing selection will lead to the population of beetles to be compared of mainly blue and toxic individuals over time

The poisonous ones have higher fitness, and natural selection will lead to more blue and toxic individuals and fewer green beetles over time

The poisonous ones have no survival advantage, and the population will be a mix of green and blue individuals over time

Correct answer:

The poisonous ones have higher fitness, and natural selection will lead to more blue and toxic individuals and fewer green beetles over time

Explanation:

Due to the fact that the blue beetles are toxic to the birds that prey on them, the birds will likely start to avoid the blue beetles and only eat the green ones. In this manner, natural selection selects against the green beetles and for the adaptations of the blue beetles. As a result, more blue beetles will survive and reproduce. Over time, this will lead to a population beetles that are mainly blue and toxic.

Example Question #5 : Understanding Natural Selection

In a particular population of island finches, smaller than average individuals suffer from reduced fitness because they cannot consume the larger seeds that appear in abundance in their habitat. Likewise, larger than average individuals of the same species suffer from reduce fitness due to increased predation from raptors on the island. What type of selection would result from this scenario?

Possible Answers:

Stabilizing selection

Directional selection

Disruptive selection

Sexual dimorphism

Correct answer:

Stabilizing selection

Explanation:

Stabilizing selection occurs when the individuals on both phenotypic extremes are selected against. In this case, individuals that are smaller or larger than the average possess a fitness disadvantage. THis scenario would result in stabilizing selection.

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