BIOLOGY 121 inheritance

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37 terms · genetics

1. How did the theory of special creation differ from Darwin's theory of evolution by natural selection?

b. The theory of special creation proposed that species are independently created and immutable over time. Darwin observed that species are related and change over time.
Correct. These are the two main differences that allowed Darwin to argue that the pattern of evolution is more consistent with what is observed in real life than is the theory of special creation.



--------------HINT: Evolution is the pattern component of Darwin's and Wallace's theory.
a. The theory of special creation proposed that vestigial traits are immutable over time. Darwin observed that they change over time.
Incorrect. Darwin argued that the observation that vestigial traits change over time was consistent with his theory of evolution and inconsistent with the theory of special creation. However, this is not the complete answer.
b. The theory of special creation proposed that species are independently created and immutable over time. Darwin observed that species are related and change over time.
Correct. These are the two main differences that allowed Darwin to argue that the pattern of evolution is more consistent with what is observed in real life than is the theory of special creation.
c. The theory of special creation proposed that species are unrelated. Darwin observed that species are related.
Incorrect. This is one difference between Darwin's observations and what is proposed by the theory of special creation, but there is another answer that is more complete.
d. The theory of special creation proposed that structural homologies result from changes that occur in species. Darwin observed that structural homologies are widespread and argued that they result from descent without modification.
Incorrect. The theory of special creation holds that species remain immutable (all structures) over time. Darwin also recognized that homologous traits did not have to be identical in different species.

2. Which of the following statements best depicts population thinking?

Individual giraffes within a population have different neck lengths.
Correct. The variation present in giraffe necks, according to Darwin, is very important to understanding the nature of the species.






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a. Human evolution is the result of a stepwise process that can be seen by examining the differences between small monkeys, apes, and humans.
Incorrect. This answer does not indicate any examination of variation within populations of any of these species. This answer represents typological thinking more than population thinking.
b. Individual giraffes in a population have the ability to stretch their necks to different lengths.
Incorrect. Population thinking concentrates on variation in measureable traits. Although behaviors can be measured, this is not the best answer choice given.
c. Individual giraffes within a population have different neck lengths.
Correct. The variation present in giraffe necks, according to Darwin, is very important to understanding the nature of the species.
d. Difference in neck length in giraffes is unimportant. Regardless of the length of an individual's neck, it is still a giraffe.

3. Which of the following is a correct restatement of Darwin's phrase "descent with modification"?

Correct. Darwin used this phrase to describe evolution. Darwin wasn't the first to describe the pattern called evolution, but he documented the pattern carefully and related it to the process called natural selection




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a. "Descent with modification" means that the species that exist today descended from other, preexisting species and that species change over time.
Correct. Darwin used this phrase to describe evolution. Darwin wasn't the first to describe the pattern called evolution, but he documented the pattern carefully and related it to the process called natural selection.
b. "Descent with modification" means that humans descended from a preexisting species that lived in trees and that humans are different from that ancestral species.
Incorrect. This answer describes just one example of evolution, but the phrase describes evolution more generally.
c. "Descent with modification" means that ancestral species of species that are alive today are more primitive and lower down on the phylogenetic tree.
Incorrect. "Descent with modification" describes the pattern of evolution that Darwin documented. He described how species change through time; "primitive" and "lower down" on the tree are not objective descriptions of how species change though time.
d. "Descent with modification" means that natural selection changes species over time.
Incorrect. "Descent with modification" describes the pattern component of evolution, not a process (natural selection) that leads to evolution.

4. Which of the following statements describes the law of succession?

Species in the fossil record were succeeded in the same region by similar species.
Correct. Before Darwin, this widespread pattern was simply reported and not interpreted. The process that caused the pattern was unknown.

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HINT: The law of succession describes a widespread pattern in the fossil record, which had been described before Darwin.
a. Species in the fossil record were succeeded in the same region by similar species.
Correct. Before Darwin, this widespread pattern was simply reported and not interpreted. The process that caused the pattern was unknown.
b. Species in the fossil record were succeeded in the same region by species more closely adapted to the current environment.
Incorrect. The law of succession describes a pattern, not the process that causes the pattern. Adaptation is a part of the process of natural selection, which was unknown before Darwin.
c. Species in the fossil record were succeeded in the same region by larger and more complex species.
Incorrect. The law of succession describes a widespread pattern that is observed in the fossil record. This pattern is not generally observed.
d. Species in the fossil record were succeeded in the same region by species that were more successful.
Incorrect. The law of succession describes a pattern of fossils, not the process that causes the pattern. Being "successful" is part of the process of natural selection, which was unknown before Darwin.

5. Why did Darwin document and describe vestigial traits?

Correct. Darwin documented and described many patterns in nature that are better described by his theory of evolution by natural selection than by any other theory. Vestigial traits could be used to illustrate that species are related, and that change through time does occur. This is also related to the homology of traits that are functional in one species, but vestigial (or reduced) in a closely related species



--------------HINT: Darwin argued that vestigial traits are better described by evolution than by the theory of special creation.
a. Vestigial traits result from divergent evolution. This is an important pattern component of the theory of evolution and is inconsistent with the theory of special creation.
Incorrect. Vestigial traits do not result from divergent evolution.
b. Vestigial traits result from convergent evolution. This is an important pattern component of the theory of evolution and is inconsistent with the theory of special creation.
Incorrect. Vestigial traits do not result from convergent evolution. They are homologous traits, not analogous traits.
c. Vestigial traits indicate that species do not change over time. This opposes the theory of evolution but is consistent with the theory of special creation.
Incorrect. Vestigial traits are homologous traits; in one species they have no function, but in others they are functional.
d. Vestigial traits indicate that species change over time. This is an important pattern component of the theory of evolution and is inconsistent with the theory of special creation.
Correct. Darwin documented and described many patterns in nature that are better described by his theory of evolution by natural selection than by any other theory. Vestigial traits could be used to illustrate that species are related, and that change through time does occur. This is also related to the homology of traits that are functional in one species, but vestigial (or reduced) in a closely related species.

6. Which traits result from convergent evolution?

Correct. Different species can have similar traits even though the trait is not derived from a common ancestor. Convergent evolution occurs when natural selection favors certain traits in different species experiencing similar selective pressures in similar environments.










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HINT: Convergent evolution leads to certain similarities among species.
a. analogous traits
Correct. Different species can have similar traits even though the trait is not derived from a common ancestor. Convergent evolution occurs when natural selection favors certain traits in different species experiencing similar selective pressures in similar environments.
b. homologous traits
Incorrect. Convergent evolution does not result in homologous traits, which are derived from a shared common ancestor.
c. developmental homologies
Incorrect. Convergent evolution does not result in developmental homologies, which occur in organisms with a shared common ancestor.
d. vestigial traits
Incorrect. Convergent evolution does not result in vestigial traits, which are derived from a shared common ancestor.

7. What three major lines of evidence did Darwin use to argue that species have changed through time?

c. Darwin's evidence was that (1) fossils frequently resemble species found in the same area today, (2) many species have gone extinct, and (3) vestigial traits are common.
Correct. Darwin used these three lines of evidence to support the idea that species have changed over time.

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changed through time?
HINT: Darwin's descriptions of the pattern component of the theory of evolution were not the first descriptions, but they have stood the test of time for their interpretation.
a. Darwin's evidence was that (1) closely related species often live in the same geographic region; (2) structural, developmental, and genetic homologies are widespread; and (3) vestigial traits are common.
Incorrect. The facts that related species live in the same region and that homologies are widespread do not indicate that species change through time.
b. Darwin's evidence was that (1) closely related species often live in the same geographic region, (2) many species have gone extinct, and (3) vestigial traits are common.
Incorrect. The fact that related species live in the same region does not indicate that species change through time.
c. Darwin's evidence was that (1) fossils frequently resemble species found in the same area today, (2) many species have gone extinct, and (3) vestigial traits are common.
Correct. Darwin used these three lines of evidence to support the idea that species have changed over time.
d. Darwin's evidence was that (1) fossils frequently resemble species found in the same area today; (2) structural, developmental, and genetic homologies are widespread; and (3) vestigial traits are common.
Incorrect. The fact that homologies are widespread does not indicate that species change through time.

8. What is considered Darwin's greatest contribution to science?

Darwin recognized the process of evolution (natural selection).
Correct. Darwin's greatest contribution to science is that he recognized that the process of evolution (natural selection) could explain the pattern of evolution (descent with modification). Evolution by natural selection is considered to be the organizing principle of biology


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a. Darwin recognized the pattern of evolution (descent with modification).
Incorrect. Darwin carefully described patterns of evolution in great detail, but others had recognized evolution as a pattern in nature long before Darwin.
b. Darwin recognized the process of evolution (natural selection).
Correct. Darwin's greatest contribution to science is that he recognized that the process of evolution (natural selection) could explain the pattern of evolution (descent with modification). Evolution by natural selection is considered to be the organizing principle of biology.
c. Darwin recognized the "original species."
Incorrect. Darwin wrote the book On the Origin of Species to explain his observations about natural selection and descent with modification. No "original species" has been recognized.
d. Darwin recognized the heritable basis of traits (genetics).
Incorrect. Genetics and the heritable basis of traits were unknown to Darwin.

9. What are the four postulates of evolution by natural selection?

d. (1) Individuals in a population vary.
(2) The variation is heritable.
(3) More offspring are produced than can survive.
(4) Individuals differ in their production of offspring.
Correct. These are succinct statements of the four postulates of evolution by natural selection.



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steps. Which of these lists of four steps will result in evolution by natural selection?
a. (1) Populations vary.
(2) The variation is heritable.
(3) More offspring are produced than can survive.
(4) Populations differ in their production of offspring.
Incorrect. Natural selection acts on individuals, not populations. Items (1) and (4) focus on populations instead of individuals.
b. (1) Individuals in a population vary.
(2) The variation is heritable.
(3) Offspring are produced that can survive.
(4) Individuals produce offspring.
Incorrect. Items (3) and (4) in this list lead to situations in which there is no selection. Individuals producing offspring that survive is a normal state of affairs, with or without evolution.
c. (1) Individuals in a population vary.
(2) The variation is heritable.
(3) More offspring are produced than can survive.
(4) Individuals have different alleles.
Incorrect. This list is missing the fourth postulate: that individuals differ in their production of offspring—the "selection" part of natural selection. It is true that individuals have different alleles, but this isn't enough to result in evolution by natural selection.

The best definition of Darwinian fitness is

d. the ability of an individual to survive and reproduce
Correct. Darwinian fitness is a characteristic of an individual that can be quantified. Survival and reproduction are important aspects of this definition because both are affected by natural selection. _






____.
HINT: Darwinian fitness is quantified for an individual by estimating how many offspring it produces relative to other individuals in the same population.
a. the ability of a population to survive
Incorrect. Darwinian fitness is measured on a per-individual basis, but there's more to fitness than survival.
b. the ability of a population of organisms to persist
Incorrect. Darwinian fitness is a characteristic of an individual, not a population.
c. the ability of an individual to stay healthy by eating well-balanced meals and exercising
Incorrect. The way we use the term fitness in everyday life is very different from the way evolutionary biologists use the term when describing organisms in the context of natural selection.
d. the ability of an individual to survive and reproduce
Correct. Darwinian fitness is a characteristic of an individual that can be quantified. Survival and reproduction are important aspects of this definition because both are affected by natural selection.

11. Darwin's theory of evolution by natural selection is testable. What does it mean for this theory to be "testable"?

11. Darwin's theory of evolution by natural selection is testable. What does it mean for this theory to be "testable"?
HINT: Theories generate testable hypotheses. These hypotheses, in turn, can be either accepted or rejected.
a. If the theory is testable and correct, then a biologist should be able to observe evolution by natural selection in a real-life population.
Incorrect. If Darwin's theory is correct, then one should be able to observe evolution by natural selection. However, this answer is incomplete.
b. If the theory is testable and incorrect, then biologists shouldn't be able to observe natural selection.
Incorrect. This answer is incomplete. Remember, natural selection isn't always occurring.
c. If the theory is testable, then biologists should be able to test each postulate of the theory separately.
Incorrect. This answer is incomplete. Darwin's theory is composed of four postulates, each of which can be tested.
d. If the theory is testable, then all of the above are true.
Correct. This is the best answer. Darwin's theory has been tested many times. Biologists have observed evolution by natural selection in hundreds of cases.

12. Resistance to a wide variety of insecticides, fungicides, antibiotics, antiviral drugs, and herbicides has recently evolved in hundreds of insects, fungi, bacteria, viruses, and plants. Why?

d. Humans are altering the environments of these organisms, and populations of these organisms are evolving by natural selection.
Correct. Humans alter the environments of these organisms so dramatically that any individual that survives to reproduce will have a tremendous fitness advantage over individuals that are susceptible. If resistance is heritable, the population will quickly evolve antibiotic resistance.

13. Which statement restates the fact that rifampin resistance in M. tuberculosis is an adaptation?

a. Rifampin resistance is a heritable trait that increases the fitness of individuals compared to susceptible individuals.
Correct. In biology, an adaptation is a heritable trait that increases the fitness of an individual with that trait relative to an individual without that trait.







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b. Rifampin resistance is caused by a point mutation in the rpoB gene.
Incorrect. This statement doesn't explain how rifampin resistance is related to fitness of individuals.
c. A mutation occurred in the rpoB gene of one cell, allowing the mutant cell to grow and divide.
Incorrect. This statement doesn't explain how the rifampin resistance trait changes fitness of individuals compared to those without rifampin resistance.
d. Drug-resistant strains now account for about 10 percent of the Mycobacterium tuberculosis-caused infections throughout the world.
Incorrect. This statement reveals that there is variation in the drug resistance trait. The statement doesn't say anything about how this variation influences the fitness of individuals.

14. Has evolution by natural selection recently occurred in populations of M. tuberculosis?

b. Yes. The frequency of the adaptive allele for drug resistance in M. tuberculosis has increased over time.
Correct. This statement gives the basic definition of evolution. Notice that evolution is fast when selection is strong! Do you think the resistance trait will reach 100 percent?




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gathered in the experiment.
a. Yes. Some people are now resistant to tuberculosis, but before they weren't. The resistance alleles have changed frequency in some human populations.
Incorrect. People have not evolved resistance to tuberculosis; the bacterial populations (M. tuberculosis) have evolved resistance to antibacterial drugs.

c. No. Evolution has not occurred, because the resistance trait occurs with a frequency of only approximately 10 percent.
Incorrect. A change in allele frequencies from about 0 percent to 10 percent in a population is definitely evolution.
d. No. M. tuberculosis is still the same species.
Incorrect. Speciation is different from evolution.

15. A modern definition of evolution is _____.

c. a change in allele frequencies in a population over time
Correct. This is the contemporary definition of evolution. Evolution occurs in populations, not individuals. Alleles were unknown when Darwin recognized the pattern of evolution, but we now know that alleles are what make traits heritable. Notice that evolution (the pattern) is separate from the process: natural selection, fitness, and adaptation.











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HINT: Darwin called evolution "descent with modification," but now we use terminology that is more quantifiable. Today, biologists still differentiate between evolution (the pattern) and natural selection (the process).
a. a change in an individual's ability to survive and reproduce as it grows older
Incorrect. Populations evolve, not individuals. Natural selection acts on individuals. It is important to be able to separate evolution (the pattern) and natural selection (the process).
b. an increase in the fitness of a population
Incorrect. Evolution is not necessarily related to changes in fitness. Evolution can occur even as individual fitnesses in a population decrease. Can you think of a scenario where this is true? It is important to be able to separate evolution (the pattern) and natural selection (the process).

d. a change in an individual's fitness over time
Incorrect. Populations evolve, not individuals. Natural selection acts on individuals. It is important to be able to separate evolution (the pattern) and natural selection (the process).

16. Can a biologist test the four postulates of evolution by natural selection when the alleles responsible for variation are not known or the molecular mechanism of adaptation has not been identified?

a. Yes. A biologist must determine whether the trait under investigation is heritable. This can be determined experimentally for quantitative traits.
Correct. Verifying heritability requires an intensive experimental effort. An experiment is the only way to demonstrate heritability for many critical quantitative trait
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b. Yes. However, a biologist must identify the DNA sequence of the gene or mutant amino acid in the protein responsible for the adaptation.
Incorrect. Identifying the molecular mechanism for adaptation is not necessary to demonstrate that a trait is heritable.
c. No. A biologist cannot verify postulate 2 of evolution by natural selection (variation is heritable) without determining the alleles responsible for variation or the molecular mechanism of adaptation.
Incorrect. There are several ways to show heritability without identifying alleles or molecules.
d. No. A biologist must demonstrate that more offspring are produced than can survive.
Incorrect. Verifying postulate 4 (more offspring are produced than can survive) is necessary when studying evolution by natural selection, but it isn't relevant to this question. How does this question relate to postulate 2?

17. During the drought of 1977, 84 percent of the medium ground finch population disappeared. The individuals that survived had deeper beaks and were larger. Given that natural selection favored large individuals with deeper beaks, how can the presence of individuals with small, pointier beaks in 1983 be explained?

Even though the majority of birds after 1977 had deeper beaks, there was variation in beak size in the population. As seed type and seed availability changed, birds with
beaks suited to exploit abundant seeds had higher reproductive success.
Correct. High rains caused plant growth to increase. These plants produced small, soft seeds. Small birds, with small and pointier beaks exploited these seeds and experienced very high reproductive success.




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a. These islands were colonized from the mainland. These small-beaked individuals must have flown over from Ecuador.
Incorrect. The data presented in the chapter does talk about present-day migration events.
b. These islands must have received immigrants from a neighboring island.
Incorrect. After the drought, no other birds from Daphne Major were found on other
islands, suggesting that there is infrequent migration between islands.

d. Researchers were not measuring juvenile birds in 1977 but did measure juvenile birds in 1983. It is a well-known fact that juvenile birds are small and have small beaks.
Incorrect. The text clearly states that all individuals were captured and marked with
individual color-coded leg bands.

18. Which conclusion cannot be drawn from the graphs shown below, concerning different characteristics of medium ground finches over a 30-year period?

The drought in 1977 caused many finches to die of starvation.
Correct. These graphs do not chart the population size of finches over this period.


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a. Overall body size of ground finches has decreased.
Incorrect. This conclusion can be drawn from the uppermost graph.
b. Beaks have become more pointed since 1973.
Incorrect. This conclusion can be drawn from the lowermost graph.
c. The drought in 1977 caused many finches to die of starvation.
Correct. These graphs do not chart the population size of finches over this period.
d. From 1985 to 2000, there was no net change in beak size.
Incorrect. This conclusion can be drawn from the middle graph.


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19. Consider the example of different color morphs found in wings of moths. Darker moths are more readily eaten than light moths. What is the explanation for certain color morphs having higher Darwinian fitness than others?
HINT: You'll need to review the hypothetical scenario given in Section

d. Moths that have lighter wings have higher Darwinian fitness because they are better camouflaged while resting on light-colored trees. When birds hunt during the day, they are more likely to eat darker individuals. Lighter individuals will survive to reproduce and have more offspring than darker individuals.
Correct. This is the best explanation. Predators are more likely to find and eat dark morphs during the day, leaving light morphs to survive and reproduce.


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fitness.
a. Juvenile moths eat different things than adults. The difference in nutrition causes a change in color as the moths age, from dark to light wings. The few juveniles that survive to become adults are lighter and have higher Darwinian fitness because they will produce offspring.
Incorrect. While diet does impact the color of wings during development, wing color doesn't change from juvenile to adult.
b. Juvenile moths develop at different temperatures. The difference in temperature causes a change in color as the moths age, from dark to light wings. The juveniles that become adults and have lighter wings have higher Darwinian fitness because they will produce more offspring than dark individuals.
Incorrect. While temperature does affect the shade of wing color during development, it does not change the color that is coded for by the genotype.
c. Moths that have darker wings actually have higher Darwinian fitness because the birds cannot see them as well as light individuals while hunting at night. These individuals will survive to reproduce and have more offspring than lighter individuals.
Incorrect. This is not a good explanation because the selection pressure of predation by birds actually occurs during the day, not at night as this answer choice suggests.

20. Lamarck proposed that evolution occurs by the inheritance of acquired characteristics. His theory of evolution can be summarized by the figure below. What is the main difference between Lamarck's view of evolution and Darwin's view of evolution?

c. Lamarck's ideas correlate to an escalator of evolution. Lamarck proposed that organisms become more complex over time.
Correct. Lamarck's view of evolution was progressive, in that simple organisms were constantly becoming more complex or "advanced" over time. Darwin's view was that evolution produces a tree of life, and individuals can become simpler or more complex depending on their environment.

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HINT: How is Darwin's phylogeny of organisms organized?
a. Lamarck proposed that individuals might change over the course of their lifetime in response to changes in environmental conditions.
Incorrect. This view did not conflict with Darwin's theory. However, Lamarck thought that the changed traits were acquired and passed on to offspring (individuals were changed after selection), whereas Darwin thought that individuals with changed traits were more fit and produced more offspring than individuals without the changed traits (populations were changed after selection).
b. Lamarck proposed that organisms might become simpler or more complex depending on their environment.
Incorrect. This theory was part of Darwin's view of evolution.
c. Lamarck's ideas correlate to an escalator of evolution. Lamarck proposed that organisms become more complex over time.
Correct. Lamarck's view of evolution was progressive, in that simple organisms were constantly becoming more complex or "advanced" over time. Darwin's view was that evolution produces a tree of life, and individuals can become simpler or more complex depending on their environment.
d. Lamarck proposed that simple forms of life are continuously being created by spontaneous generation.
Incorrect. This view is not addressed by Darwin's theory of evolution.
21. Arctic toothfishes live in very cold water year-round. These fishes express

21. Arctic toothfishes live in very cold water year-round. These fishes express unique genes that code for anti-freeze proteins. The production of anti-freeze proteins in these fish is an example of _____.

b. an adaptation
Correct. The expression of the genes coding for the production of anti-freeze proteins is an adaptation to the frigid waters where arctic toothfishes are found. This is not a seasonal response.


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HINT: Recall the example of the wood frog and consider both similarities and differences between arctic toothfishes and wood frogs.
a. acclimation
Incorrect. This is when an individual's phenotype changes in response to an environmental change.

c. an acquired characteristic
Incorrect. Organisms do not acquire characteristics useful for surviving in their environments.
d. genetic correlation
Incorrect. Genetic correlation is a constraint that refers to traits being expressed through pleiotropy. There is no mention of other traits correlated with the genes causing expression of anti-freeze proteins.

1. A population is _____.

Scott Freeman
Biological Science, 3e
Chapter Quiz - 25

HINT: Understanding the concept of a population is key to understanding evolutionary change. Review the introductory passage of Chapter 24 for an idea of how the textbook uses this term.
a. any group of many individuals of the same species
Incorrect. The definition of a population is more specific than this. Would you expect the population of humans in Manhattan to include everybody that lives in Los Angeles?
b. a group of individuals that live in the same area and regularly interbreed
Correct. Within a species, if there are two groups of individuals that don't interbreed, they are not part of the same population.
c. a group of interacting species that live in the same area
Incorrect. A population is composed of individuals of the same species. A community is a group of interacting species.
d. two or more groups that regularly interbreed
Incorrect. The concept of a "group" is vague; populations are composed of individuals of the same species that live in the same area.

If the frequency of allele A1 in a population is 0.4 and the frequency of allele A2 is 0.6 in the same population, what is the frequency of the heterozygotes A1A2 in the next generation?

HINT: Review the frequency of genotypes in the Hardy-Weinberg principle.
a. 0.16
Incorrect. This is the frequency p2 of the genotype A1A1.
b. 1
Incorrect. This is the frequency of the three possible genotypes: A1A1, A1A2, and A2A2.
c. 0.36
Incorrect. This is the frequency q2 of the genotype A2A2.
d. 0.48
Correct. This is the frequency 2pq of the heterozygote A1A2.

19. Which characteristic is common to both inbreeding and sexual selection?

HINT: Review the impact of inbreeding on sexual selection.
a. They both lead to adaptation.
Incorrect. Only sexual selection produces adaptive change.
b. They both cause evolutionary change.
Incorrect. Inbreeding alters genotypic frequencies, not allele frequencies, so it doesn't result in evolution.
c. They both affect all loci in a genome.
Incorrect. Inbreeding affects all loci, whereas sexual selection affects only loci that code for mate choice traits.
d. They are both forms of nonrandom mating.
Correct. This is the only true statement. Nonrandom mating has very different consequences for a population, depending on whether it occurs because of sexual selection or because of inbreeding. What are these different consequences?

18. Which of the following is not associated with inbreeding?

HINT: What is inbreeding?
a. Allele frequencies change in a population.
Correct. Inbreeding does not change allele frequencies. This means that inbreeding is not a mechanism for evolution, although inbreeding can cause fitness reductions in individuals, a phenomenon known as inbreeding depression.
b. The frequency of homozygotes increases in a population.
Incorrect. Homozygous genotypic frequencies increase in inbreeding populations, reducing the amount of genetic diversity within individuals.
c. Individuals in a population experience reduced fitness.
Incorrect. Inbreeding depression is a fitness reduction that happens to the offspring of related parents.
d. Individual plants self-fertilize.
Incorrect. Self-fertilization is the most extreme form of inbreeding.

3. The Hardy-Weinberg principle acts as a null model because it describes the relationship between allele and genotypic frequencies under what circumstances?
HINT: When do genotypic frequencies conform to Hardy-Weinberg proportions?

a. when none of the four evolutionary forces is acting, and mating is random
Correct. This is the circumstance that causes genotypic proportions to conform to Hardy-Weinberg predictions.
b. when new species differentiate
Incorrect. Species differentiation is not relevant to the Hardy-Weinberg principle. Although evolutionary processes can lead to speciation, this is not a circumstance where the Hardy-Weinberg model acts as a null hypothesis.
c. when evolution by natural selection increases the fitness of individuals
Incorrect. When natural selection occurs in a population, genotypic proportions may not conform to Hardy-Weinberg proportions.
d. when individuals in a population are not mating randomly with respect to the HLA genotype
Incorrect. A population that is not mating randomly will not conform to Hardy-Weinberg genotypic expectation.

17. Which of the following biological processes leads to adaptation?

HINT: Over the long time scale, adaptive evolution is probably the most important factor in making the world the rich, diverse place that it is.
a. mutation
Incorrect. Mutation causes random changes, not adaptive change.
b. gene flow
Incorrect. Gene flow does not cause adaptive change.
c. genetic drift
Incorrect. Drift causes random changes, not adaptive change.
d. natural selection
Correct. Only selection can lead to adaptive evolutionary change.

2. If the frequency of allele A1 in a population is 0.4 and the frequency of allele A2 is 0.6 in the same population, what is the frequency of the heterozygotes A1A2 in the next generation?

4. Which of the following is not a null model?
HINT: Consider that the Hardy-Weinberg principle represents a null model.
a. the Hardy-Weinberg model
Incorrect. This is a null model because it describes what happens when no evolutionary processes occur.
b. a model of what happens to a locus with no genetic diversity
Incorrect. This is a null model of what happens when no evolutionary forces are acting.
c. a model that describes what happens during an artificial selection experiment
Correct. This is not a null model because it describes what happens when evolution occurs. If a scientist can't reject a hypothesis about evolution, then we say, "We can't reject the null model."
d. a model of what happens when no evolutionary forces are acting in a population
Incorrect. This is a null model of what happens when no evolutionary forces are acting.

5. Which statement is the best contemporary definition of evolution?

HINT: Remember that evolution is a pattern that is observed.
a. Evolution is natural selection in two populations.
Incorrect. Natural selection is one of the four processes that result in evolution.
b. Evolution is the same as Hardy-Weinberg equilibrium.
Incorrect. Hardy-Weinberg equilibrium occurs when there is no evolution.
c. Evolution is a change in allele frequencies over time within a population.
Correct. This is the best definition of evolution. Notice that there is a quantifiable pattern, but no mechanism (or process) is described.
d. Evolution is an example of Mendelian inheritance.
Incorrect. Mendelian inheritance causes no change in allele frequencies.

16. Which evolutionary process is least important for conservation biologists concerned about the future direction of evolutionary change in endangered populations?

HINT: Think about what processes cannot be managed or influenced by conservation scientists.
a. migration
Incorrect. Introduction of new individuals into an endangered population can be beneficial or detrimental. This process is an important consideration.
b. genetic drift
Incorrect. This process can be controlled by changing the number of individuals in a population. It is very important to conservationists.
c. mutation
Correct. Mutations do not occur often enough to cause major evolutionary change.
d. inbreeding
Incorrect. This process can be regulated in captive breeding programs and is very important for conservation scientists.

6. Which scenario illustrates heterozygote advantage?
HINT: Compare the fitness of heterozygous and homozygous individuals when there is heterozygote advantage.

a. A population consists of more heterozygous individuals than expected under the Hardy-Weinberg principle.
Incorrect. Heterozygote advantage may result in this situation, but other processes may, too.
b. Individuals heterozygous at a given locus are more fit than homozygous individuals.
Correct. Heterozygote advantage is a pattern of natural selection that tends to maintain genetic diversity within a population.
c. Individuals in a population are nonrandomly mating without inbreeding depression.
Incorrect. Heterozygote advantage is a type of natural selection.
d. Parents with similar HLA alleles produce more offspring than parents with dissimilar HLA alleles.
Incorrect. This example illustrates a condition that is the opposite of heterozygote advantage.

15. Which of the following scenarios, involving mutation, may cause evolutionary change?

HINT: Consider the average mutation rate in humans, and what effect mutation has on allele frequencies in a population.
a. a mutation that occurs in areas where there is high UV radiation, causing thymine dimers, so only human populations in those areas are affected by mutation
Incorrect. There are many different mutagens. Only those mutations that are transmitted to offspring via gametes, not in somatic cells, can be passed on to offspring and have the potential to change allele frequencies within a population.
b. a mutation that confers antibiotic resistance in bacteria
Correct. A mutation like this would result in a selective advantage for individuals with the mutation.
c. a mutation that occurs in a single individual within a small population
Incorrect. In a small population, alleles are more likely to be lost due to drift than in large populations.
d. a population that experiences no mutation
Incorrect. Although highly unlikely, mutation is the ultimate source of genetic
variation. Without mutation, evolution would eventually stop.

14. Genetic diversity is required for natural selection to act, but natural selection can reduce or eliminate diversity. What forces restore or maintain diversity of a population?
HINT: Consider the four evolutionary mechanisms

described in Chapter 25.
a. Hardy-Weinberg equilibrium
Incorrect. Hardy-Weinberg equilibrium occurs when allele frequencies don't change over time—the absence of evolution.
b. inbreeding
Incorrect. Inbreeding, where like genotypes only mate with like genotypes, does not change allele frequencies. By itself, inbreeding does not affect diversity within a population.
c. sexual selection
Incorrect. Sexual selection is usually a form of directional selection that tends to reduce genetic diversity in loci that code for mate choice traits.
d. gene flow
Correct. Gene flow can introduce new alleles and maintain diversity in populations.

13. An important consequence of gene flow in natural populations is that it _____.

HINT: Consider that gene flow is a movement of alleles, carried by individuals, between populations. How does gene flow affect populations?
a. increases the mutation rate among sedentary organisms
Incorrect. Mutation is a random process and occurs independent of gene flow.
b. moves individuals from one habitat to another on a seasonal basis
Incorrect. Gene flow refers not to seasonal movement but to movement of alleles.
c. tends to separate allele frequencies among populations
Incorrect. Gene flow tends to homogenize allele frequencies among populations.
d. tends to reduce genetic differences among populations
Correct. This is the major effect of gene flow. On one hand, the consequences of increased gene flow for endangered populations might be beneficial if genetic diversity is being lost by drift. On the other hand, increased gene flow might homogenize populations that are distinct because they are adapted to local conditions.

7. Which of the following is not a result of disruptive selection?

HINT: Recall Figure 25.4a-c, figures representing the distributions of traits before and after selection, when answering this question.
a. Disruptive selection causes a change in the mean value for a trait.
Correct. Changes in the mean value of a trait are the result of directional selection.
b. Disruptive selection is the result of individuals with extreme phenotypes having higher fitness.
Incorrect. Disruptive selection is the result of individuals at the extremes of the trait distribution having higher fitness.
c. Disruptive selection, like stabilizing selection, causes no change in the mean value of a trait.
Incorrect. There is no change in the mean value for a trait with either stabilizing or disruptive selection. However, stabilizing selection reduces variation in a population.
d. Disruptive selection results in increased variation in a population.
Incorrect. Disruptive selection does cause an increase in variation.
8. Which of the following examples of natural selection in action would tend to increase the genetic variation in the population?
HINT: Remember that natural selection requires variation to operate.
a. Natural selection causes dragonflies to evolve longer tails.
Incorrect. This is an example of directional selection, which tends to reduce the genetic diversity of a population.
b. Alpine skypilots evolve large flowers above the timberline and small flowers below the timberline.
Correct. Disruptive selection or selection for extreme phenotypes tends to increase variation in that trait.
c. Natural selection simultaneously selects against heavy field mice (they starve during winter) and light field mice (they freeze during winter).
Incorrect. This is an example of stabilizing selection, which tends to reduce genetic variation in a population.
d. Natural selection acts on beak size in finches such that those individuals able to eat small, soft seeds survive through the winter.
Incorrect. This is an example of directional selection.
9. Which statement most fully characterizes the fundamental asymmetry of sex?
HINT: The fundamental asymmetry of sex is an important component in theories of sexual selection.
a. Female fitness is limited mostly by the ability to get resources for producing eggs and rearing young, while male fitness is limited by the ability to attract females.
Correct. This is the fundamental idea of the asymmetry of sex in a nutshell.
b. Female fitness is limited mostly by the ability to attract males, while male fitness is limited by the ability to get resources for provisioning the female.
Incorrect. Female fitness is not generally limited by the ability to attract males.
c. Female fitness is limited mostly by the ability to get resources for producing eggs and rearing young, while male fitness is limited by the ability to get resources for provisioning the female.
Incorrect. Male fitness may be limited by the ability to get resources, but this is only one way of attracting mates.
d. Female fitness is limited mostly by the ability to attract males, and male fitness is limited by the ability to attract females.
Incorrect. There is no asymmetry in this statement.
10. Which populations would be affected most by random genetic drift?
HINT: Genetic drift is often studied in island populations.
a. large populations
Incorrect. The larger a population is, the less random genetic drift affects allele frequencies.
b. small populations
Correct. Random genetic drift affects allele frequencies more drastically as population size decreases.
c. migrating populations
Incorrect. Whether or not a population migrates does not influence genetic drift.
d. fixed populations
Incorrect. "Fixed" in the evolutionary sense means that an allele has reached a frequency of 100 percent; the other allele would be lost and have a frequency of 0 percent. If there is no variation, then drift cannot change allele frequencies.
11. Which population would not be affected by a founder effect?
HINT: What is a founder event?
a. finches that colonized the Galápagos Islands
Incorrect. These finches emigrated to a new geographic area and founded a new population, so they would be affected by a founder effect.
b. Tahitians and English mutineers on the Pitcairn Islands
Incorrect. These individuals emigrated to a new geographic area and founded a new population, so they would be affected by a founder effect.
c. Ashkenazi Jews that settled in Eastern Europe
Incorrect. These individuals emigrated to a new geographic area and founded a new population, so they would be affected by a founder effect.
d. survivors of a typhoon in the Pingelap Atoll
Correct. This population did not move to a new geographic area. Instead, it experienced a reduction in the number of alleles in the population and thus would be affected by a genetic bottleneck.
12. Which pattern observed in natural populations is not caused by a genetic bottleneck?
HINT: A genetic bottleneck is an example of genetic drift.
a. lack of variation in whooping crane vocalizations
Incorrect. The worldwide population of whooping cranes recently became much smaller, reducing allelic diversity in this species.
b. Fixed loci in endangered plant populations
Incorrect. Bottlenecks are a major concern because they reduce genetic diversity in endangered species. Small populations are more susceptible to the effects of genetic drift.
c. long, thin necks in giraffes
Correct. Bottlenecks are unlikely to lead to adaptive traits such as long necks in giraffes. Long, thin necks in giraffes are the result of natural selection.
d. extremely low genetic diversity in cheetahs
Incorrect. A genetic bottleneck probably caused the observed low genetic diversity in cheetah populations worldwide.

1. Which of the following is considered by some to be a disadvantage of the phylogenetic species concept?
HINT: Consider the differences between each of the species concepts.

Scott Freeman
Biological Science, 3e
Chapter Quiz - 26

a. The phylogenetic species concept characterizes species based on ancestry, and only monophyletic groups are recognized.
Incorrect. This is an advantage of the phylogenetic species concept.
b. The phylogenetic species concept utilizes many characteristics to establish relatedness between different species.
Incorrect. This is an advantage of the phylogenetic species concept. Phylogenetic trees can be constructed using morphological, behavioral, and genetic data.
c. The phylogenetic species concept can be used for any organism, including those that reproduce asexually.
Incorrect. This is an advantage of the phylogenetic species concept.
d. The phylogenetic species concept has yielded very few estimated phylogenetic trees, and for a small number of groups.
Correct. Although the number of phylogenies for different groups of organisms is currently increasing, there are not a large number of phylogenies for many groups on the tree of life.
2. Which of the following would not be a good example of prezygotic reproductive isolation?
HINT: Think about what would not prevent interspecific matings.
a. Two bird species live in the same area and, while similar in plumage, engage in dramatically different courtship dances.
Incorrect. Courtship dances often contain information about species identity.
b. Two beetle species are superficially similar in appearance, but the structure of the male penis and the female genitalia prevents males from one species from copulating with females of the other.
Incorrect. This is an example of mechanical isolation.
c. Two plant species have wind-dispersed pollen that lands on the styles and grows a pollen tube through the ovary of either species; however, in hybrid matings, the sperm cannot fertilize the ovum.
Incorrect. The gametes never unite, suggesting some kind of gametic incompatibility.
d. Two frog species meet and can mate with each other, but the hybrid offspring are infertile.
Correct. These frogs apparently are not completely prezygotically isolated; they mated, but the resulting zygotes are not viable.
3. Which of the following situations is a result of reproductive isolation caused by differences in timing?
HINT: What sort of timing event would maintain reproductive isolation between a pair of species?
a. Males and females within a species are active at different times of day.
Incorrect. Difference in activity patterns between the sexes within a species may have nothing to do with isolation from other species.
b. Males and females of one species form lifetime pair bonds, whereas males and females of a closely related species are polygamous.
Incorrect. Frequency of mating with different mates has nothing obvious to do with isolation from other species.
c. Males and females of one species breed in early springtime, whereas males and females of a closely related species breed in early summer.
Correct. The seasonal difference in breeding season would mean that members of one species would never have the opportunity to mate with the other species.
d. Males and females of one species breed in oak trees, while males and females of a closely related species breed in maples.
Incorrect. This is an example of spatial isolation, not temporal isolation.
4. A monophyletic group would be best described as a grouping of _____.
HINT: What species would you include in a monophyletic grouping?
a. all species descended from a common ancestor, including that ancestor
Correct. A monophyletic group includes a node and all the branches coming off that node.
b. all species descended from a common ancestor, excluding that ancestor
Incorrect. The ancestor should be included in a monophyletic grouping.
c. all species that share a similar set of traits
Incorrect. Organisms can share similar traits through convergent evolution or through descent.
d. some of the most closely related species, but not all species that are descended from a common ancestor
Incorrect. The ancestor and all species descended from a common ancestor should be included in a monophyletic grouping.
5. Paleontologists studying fossilized therapsids (a group of mammal-like reptiles that are now extinct) would probably use which of the following species concepts?
HINT: What characteristics can be used to identify a species in the fossil record?
a. biological species concept
Incorrect. How would you assess reproductive isolation in an extinct lineage?
b. morphospecies concept
Correct. Paleontologists normally have little choice but to use morphospecies concepts because they cannot test reproductive isolation or the genetic relatedness of most fossils.
c. phylogenetic species concept
Incorrect. Generally, you cannot extract DNA from a fossil, so genetic relationships cannot be assessed.
d. none of the above; fossil species cannot be classified
Incorrect. These animals are classified; think of a book about dinosaurs you may have looked at or a natural history museum you've visited.
6. A subspecies is _____.
HINT: How are subspecies classifications different from biological species classification?
a. a species that is descended from another species
Incorrect. All extant species are descended from other species.
b. each population of a biological species
Incorrect. If this were true, the words subspecies and population would mean the same thing.
c. a population that is somewhat distinctive in behavior or appearance from other similar populations, but not different enough to be considered a separate species
Correct. The problem with the designation subspecies is that it is arbitrary; many populations within a species may differ morphologically or behaviorally, but these differences do not isolate the populations.
d. a population that is in the process of diverging from another population of the same species but is not quite reproductively isolated
Incorrect. Although this may be true of a particular subspecies, it is not a general characteristic.
7. Which event would not result in allopatric speciation?
HINT: What is allopatric speciation?
a. an earthquake that isolates a population of rodents on a mountain
Incorrect. Allopatric speciation can occur as a result of vicariance events.
b. development of different antler sizes between male and female reindeer
Correct. Allopatric speciation occurs when populations are separated geographically, or by a barrier that inhibits gene flow.
c. migration of birds to an island
Incorrect. Allopatric speciation can occur as a result of dispersal.
d. a flood that separates a population of frogs onto opposite sides of a large lake
Incorrect. Allopatric speciation can occur as a result of vicariance events.
8. Peter and Rosemary Grant observed a small group of the large ground finch that colonized Daphne Major in the Galápagos Islands. Within a few years, the descendants of the colonists had evolved beaks that were much larger than those in the original source population. What factors did the Grants think influenced this evolution?
HINT: What evolutionary processes are driving evolution on Daphne Major?
a. The original small size of the colonist pool probably resulted in divergence due to founder effects and genetic drift.
Incorrect. A small founding population can certainly change due to genetic drift, but is this the only thing affecting the finches?
b. Natural selection occurred due to the larger seeds found on Daphne Major compared to the ancestral island.
Incorrect. Beak size in Darwin's finches is often related to changes in seed size and hardness, but is this the only factor affecting the finches?
c. Reinforcement occurred due to postzygotic isolation on secondary contact.
Incorrect. This is not a situation involving secondary contact.
d. Both the first and second choices were probably important.
Correct. Although the studies of finches on other islands strongly suggest that natural selection is driving the divergence in beak size, one cannot rule out genetic drift because of the small founding population.
9. Which of the following represents a vicariant event that may lead to speciation?
HINT: What is the definition of vicariance?
a. In a population of beetles, one leaves and moves to a new population.
Incorrect. This scenario represents a dispersal event.
b. A small subset of individuals in a population of mainland birds leaves and starts a new population on a small neighboring island.
Incorrect. This scenario is a colonization event.
c. During a strong storm, a river changes course and flows through a population of ground beetles; the river is now a barrier.
Correct. This is a vicariant event. The ground beetle population is now permanently divided. Subpopulations on either side are now separated in allopatry.
d. Some individuals of flightless insects colonize a new food plant also present in the distribution of their original population, and no longer interact with individuals from the original population.
Incorrect. This would be an example of divergence in sympatry, not allopatry.
10. Vicariance is best described as a _____.
HINT: Think about the major types of geographic speciation.
a. pattern of speciation in which a population is subdivided by a geographic barrier
Correct. An example would be the raising of the Isthmus of Panama approximately 3 million years ago (mya), which separated isolated marine populations in the Pacific Ocean and Caribbean Sea.
b. kind of speciation in which a small propagule founds a population on a habitat island
Incorrect. This is a founder event, not vicariance.
c. pattern of speciation whereby new species evolve reproductive isolation in sympatry
Incorrect. Vicariance occurs in allopatry, not sympatry.
d. technique for constricting phylogenetic trees based on vicariant traits shared by all members of a taxon
Incorrect. Vicariance refers to a pattern of speciation, not a phylogenetic method.
11. Which of the following evolutionary forces could be important for population differentiation in allopatric speciation?
HINT: Think about mechanisms of evolution that could act independently in allopatric populations.
a. genetic drift
Incorrect. Genetic drift certainly can lead to differentiation, especially if the size of one population is small, but this may not be the best answer choice.
b. natural selection
Incorrect. If the two populations experienced different selection pressures, then the populations would diverge. Still, there might be a better answer.
c. nonrandom mating
Incorrect. If individuals chose mates based on phenotype or if inbreeding was relatively common, this could cause divergence between the populations. However, there may be a better answer.
d. all of the above
Correct. All of these evolutionary forces have the potential to cause divergence in allopatric populations.
12. Which of the following events would best be described as a case of speciation in sympatry?
HINT: Think about how sympatric populations can become reproductively isolated.
a. A population of lizards is subdivided by a natural barrier and subsequently diverges to form two species that cannot interbreed.
Incorrect. This is vicariance, not sympatric speciation.
b. A new, isolated population of fruit flies is founded by a small group of colonists, who then diverge from the ancestral source population.
Incorrect. This is allopatric speciation with a group of founding colonists, not sympatric speciation.
c. An individual hermaphroditic plant undergoes meiotic failure, producing diploid pollen and ovules; these self-fertilize, germinate, and grow into several fully fertile tetraploid plants.
Correct. The change in ploidy took place without spatial or temporal separation; the doubling of the genome immediately isolated the new tetraploid species from its parental species.
d. Speciation cannot take place in sympatry, only in allopatry where geography poses a barrier to gene flow.
Incorrect. It once was thought that sympatric speciation was less likely than allopatric speciation, but there are now many examples of speciation in sympatry.
13. Why have soapberry bugs feeding on nonnative hosts evolved shorter beaks than those feeding on their native host plant?
HINT: What is the agent of selection in this example?
a. The nonnative host species have smaller fruits; natural selection favors bugs with a shorter beak length on these hosts.
Correct. Bugs with shorter beaks are at a selective advantage on the introduced hosts, whereas bugs with longer beaks are at an advantage on the native hosts.
b. A small population of soapberry bugs with short beaks colonized the nonnative hosts; the differentiation is due to genetic drift.
Incorrect. Genetic drift may play a role in divergence here; however, other evolutionary forces, like natural selection, are probably more important.
c. This difference is due to a change in ploidy, resulting in a genetically differentiated population on nonnative hosts.
Incorrect. Speciation by polyploidy is common in plants, but almost never happens in insects.
d. Beak size is phenotypically plastic; the changes seen are not genetic and do not reflect genetic differentiation.
Incorrect. The data presented are not adequate to rule out this possibility. If one reared offspring of long- and short-beaked bugs on a common host and still observed a difference, it would suggest genetic differentiation. There is, however a better answer than this one!
14. Which of the following statements about autopolyploid individuals is correct?
HINT: What does it mean for an individual to be polyploid, and how does this result from autoploylpoidy versus allopolyploidy?
a. Autopolyploid individuals result from a mating between individuals of different species.
Incorrect. They result from a mating between individuals of the same species.
b. Autopolyploid individuals contain more than two sets of chromosomes.
Correct. All polyploid individuals contain more than two sets of chromosomes.
c. Autopolyploid individuals can be produced from nondisjunction events in mitosis.
Incorrect. They can be produced from nondisjunction events in meiosis.
d. Autopolyploid individuals are formed by combining gametes that have two distinct sets of chromosomes.
Incorrect. They are formed by combining gametes that have the same sets of chromosomes, because they are formed from individuals of the same species.
15. How can allopolyploid individuals result in new species?
HINT: How can polyploid individuals become reproductively isolated?
a. Polyploid individuals still produce viable offspring from matings with either parent species.
Incorrect. This scenario would result in individuals that are not reproductively isolated, and speciation will not occur.
b. Polyploid individuals have lower fitness than either parent species, and are selected against by natural selection.
Incorrect. If they have lowered fitness, then natural selection should remove them from the population.
c. Polyploid individuals can only reproduce with other polyploid individuals, but cannot interbreed with either parent species.
Correct. This scenario represents reproductive isolation, and a speciation event. This also exemplifies how speciation can occur over a single generation.
d. Polyploid individuals are sterile and do not produce viable offspring.
Incorrect. This is a postzygotic isolating mechanism and does not result in a speciation event.
16. Imagine two populations descended from a single bird species. After a period of isolation in allopatry, the populations resume inhabiting the same region. Assuming that the only differences between the populations are those listed, which of the following factors would most likely prevent interbreeding?
HINT: What factors would cause reproductive isolation between two species?
a. Population A rests in the upper branches of trees during foraging bouts; population B rests on the ground.
Incorrect. Just because the two species rest in different places does not mean they are reproductively isolated.
b. Population A forages by picking insects off leaves; population B forages by tearing open ant nests and eating the ants.
Incorrect. Eating different foods, even in different places, does not mean that the species are reproductively isolated.
c. Population A performs its mating calls in the upper branches of trees; population B performs them on the ground.
Correct. Mating calls lure in mates for breeding. Calling from the treetops will attract potential mates to the treetops. Calling from the ground will attract potential mates to the ground. Thus, mating will never take place between the "wrong" partners.
d. Population A nests in oak trees; population B nests in maple trees.
Incorrect. Where a population nests may have nothing to do with whom it mates with.

17. Reinforcement of speciation refers to _____.

HINT: What kind of selection is imposed on offspring from a pair of species by strong postzygotic isolation?
a. natural selection favoring mechanisms of prezygotic isolation imposed by reduced fitness in hybrid offspring
Correct. Organisms that can identify members of the other species and avoid mating with them will not lose fitness due to hybrid inviability. Those individuals will be at a selective advantage over those that lack the prezygotic isolating mechanism.
b. natural selection to increase postzygotic isolation imposed by differences in courtship rituals or pollination strategies
Incorrect. If individuals can avoid mating with the wrong species, the fitness of hybrid offspring does not matter.
c. genetic drift that causes two subsets of a population to become more differentiated
Incorrect. Reinforcement is a type of natural selection; genetic drift is not.
d. the evolution of compatibility between hybrids that leads to the fusion of two diverging populations
Incorrect. This is not reinforcement but a weakening of speciation.
18. When two populations come into contact after a long period of divergence in allopatry, which of the following is the least likely possibility?
HINT: Consider the processes that result in divergence between two populations.
a. The two populations meet and form a hybrid zone where both species interbreed and form viable offspring.
Incorrect. This is a possibility. If the time since isolation has been short, the degree of divergence may not have been enough to render the populations reproductively isolated.
b. The two populations meet and hybrid offspring from the two populations have reduced fitness.
Incorrect. This would be the result of reinforcement.
c. The two populations meet and mating does not produce any offspring.
Incorrect. This is a possibility. Reinforcement is complete, and there is reproductive isolation.
d. The two populations meet and there have been no genetic changes between the populations. Each population is identical to before the separation.
Correct. It is highly unlikely that no changes have occurred. There must have been some mutation, or effects of drift while the populations were separated.
19. Why was mitochondrial DNA so useful in the study of the hybrid zone between Townsend's warbler and hermit warblers?
HINT: What could researchers say about the hybrids solely on the basis of the mtDNA marker?
a. mtDNA is maternally inherited, so the researchers were able to discover that most hybrids resulted from Townsend's males mating with hermit females.
Correct. Hybrid warblers always contained hermit mitochondria, suggesting that hermit females would mate with Townsend's males. If Townsend's females mated with hermit males, then some hybrids would contain Townsend's mitochondria.
b. mtDNA is easy to extract, so the researchers could obtain lots of genetic information about the hybrids.
Incorrect. This is true; however, the ease of extracting mtDNA does not give any information about the actual hybrid zone between these two species.
c. mtDNA shows that reinforcement has been occurring within this hybrid zone.
Incorrect. Reinforcement results in a change in prezygotic isolation for species in sympatry; changes in behavior or morphology that allow prezygotic isolation are unlikely to involve mitochondrial genes.
d. mtDNA is inherited from both parents, like most of the nuclear genetic material. Any gene could have been used in this study.
Incorrect. mtDNA is maternally inherited.
20. Which of the following findings would not support the hypothesis that the sunflower Helianthus anomalus originated as a hybrid between H. annuus and H. petiolaris?
HINT: What characteristics would hybrids share?
a. H. anomalus phenotypically resembles hybrids between H. annuus and H. petiolaris.
Incorrect. Hybrids usually exhibit a mixture of the parental species traits.
b. Most of the gene sequences in H. anomalus are different from either H. annuus or H. petiolaris.
Correct. Hybrids would be expected to have gene sequences in common with one or the other of the parental species.
c. Experimental crosses between H. annuus and H. petiolaris produced hybrids with similar species-specific patterns of DNA sequences as found in H. anomalus.
Incorrect. This finding suggests that there is selection within the hybrid genome; specific combinations of genes yield higher fitness than a random mixture of genes from the parent species.
d. H. annuus and H. petiolaris hybridize in the geographic region where H. annuus is found.
Incorrect. One would expect hybrids to occur in a region where both parent species are present.

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