Answers to End-of-Chapter Questions – Brooker et al ARIS site
Chapter 25
Test Yourself Questions
1. Macroevolution refers to the evolutionary changes that
a. occur in multicellular organisms.
b create new species and groups of species.
c. occur over long periods of time.
d cause changes in allele frequencies.
e. occur in large mammals.
Answer: b. Macroevolution refers to the evolutionary changes that create new species and groups of
species.
2. The biological species concept classifies a species based on
a. morphological characteristics.
b. reproductive isolation.
c. the niche the organism occupies in the environment.
d. genetic relationships between an organism and its ancestor.
e. both a and b.
Answer: b. The biological species concept classifies a species based on reproductive isolation from
other organisms.
3. Which of the following would be considered an example of a postzygotic isolating mechanism?
a. incompatible genitalia
b. different mating seasons
c. incompatible gametes
d. mountain range separating two populations
e. fertilized egg fails to develop normally
Answer: e. The failure of a fertilized egg to develop normally is an example of a postzygotic isolating
mechanism.
4. Hybrid breakdown occurs when species hybrids
a. do not develop past the early embryonic stages.
b. have a reduced life span.
c. are infertile.
d. are fertile but produce offspring with reduced viability and fertility.
e. produce offspring that only express the traits of one of the original species.
Answer: d. Hybrid breakdown occurs when fertile hybrids are produced but subsequent generations
exhibit reduced viability or fertility.
5. The evolution of one species into a different species is
a. hybridization
b. anagenesis
c. cladogenesis
d. adaptive radiation
e. microevolution
Answer: b. Anagenesis is the transformation of one species into a different species.
6. Founder events may lead to rapid speciation because of
a. differences in natural selection on the new population versus the original population.
b. genetic differences due to genetic drift.
c. enhanced gene flow between the new population and the original population.
d. all of the above.
e. a and b only.
Answer: e. Founder events may result in rapid speciation because of reduced gene flow, differences in
selection pressure, and genetic changes as a result of genetic drift.
7. A major mechanism of speciation in plants but not animals is
a. anagenesis.
b. polyploidy.
c. hybrid breakdown.
d. genetic changes that alter the organism’s niche.
e. both a and d.
Answer: b. Polyploidy, resulting from changes in chromosome number, is a major mechanism of
speciation in plants. About 30 to 50% of ferns and flowering plants are polyploid.
8. The concept of punctuated equilibrium suggests that
a. the rate of evolution is constant, with short time periods of no evolutionary change.
b. evolution occurs gradually over time.
c. small genetic changes accumulate over time to allow for phenotypic change and speciation.
d. long periods of little evolutionary change are interrupted by short periods of major
evolutionary change.
e. both b and c.
Answer: d. Punctuated equilibrium suggests that long periods of little evolutionary change are
interrupted by short periods of major change.
9. Researchers suggest that an increase in the number of Hox genes
a. would lead to reproductive isolation in all cases.
b. could explain the evolution of color vision.
c. allows for the evolution of more complex body forms.
d. results in the decrease in the number of body segments in insects.
e. all of the above.
Answer: c. Hox genes control the formation of different regions of the body. An increase in the number
of these genes could introduce more complexity in body forms.
10. The observation that the mammalian Pax6 gene and the Drosophila eyeless gene are homologous
genes that promote the formation of different types of eyes suggests that
a. Drosophila eyes are more complex.
b. mammalian eyes are more complex.
c. eyes arose once during evolution.
d. eyes arose at least twice during evolution.
e. eye development is simple process.
Answer: c. Because the same transcription factor controls both types of eyes, it suggests that both types
of eyes evolved from the same simple eye. In other words, eyes arose only once during evolution.
Conceptual Questions
1. Define species.
Answer: A group of organisms that maintains a distinctive set of attributes in nature.
2. Distinguish between prezygotic isolating mechanisms and postzygotic isolating mechanisms and give
an example of each.
Answer: Prezygotic isolating mechanisms prevent the formation of the zygote and an example is
mechanical isolation, the incompatibility of genitalia. Postzygotic isolating mechanisms act after the
formation of the zygote and an example would be inviability of the hybrid that is formed. (Other
examples as shown in Figure 25.2 would also be correct.)
3. Define punctuated equilibrium.
Answer: According to this idea, species exist relatively unchanged for many generations. During this
period, the species is in equilibrium with its environment. These long periods of equilibrium are
punctuated by relatively short periods during which evolution occurs at a far more rapid rate.
Experimental Questions
1. What did Podos hypothesize regarding the effects of beak size on a bird's song? How could changes
in beak size and shape lead to reproductive isolation among the finches?
Answer: Podos hypothesized that the morphological changes in the beak would also affect the birds’
songs. A bird’s song is an important component for mate choice. If changes in the beak alter the song of
the bird, this would impact reproductive ability. Podos suggested that changes in the beak morphology
could thus lead to reproductive isolation among the birds.
2. How did Podos test the hypothesis that beak morphology caused changes in the birds’ songs?
Answer: Podos first caught male birds in the field and collected data on beak size. The birds were
banded for identification and released. Later, the banded bird’s songs were recorded and analyzed for
range of frequencies and trill rates. The results were then compared to similar data from other species
of birds to determine if beak size constrained the frequency range and trill rate of the song.
3. Did the results of Podos’ study support his original hypothesis? Explain. What is meant by the phrase
“by-product of adaptation” and how does it apply to this particular study?
Answer: The results of the study did indicate that natural selection on beak size due to changes in diet
could lead to changes in song. Considering the importance of bird song to mate choice, the changes in
the song could also lead to reproductive isolation.
The phrase “byproduct of adaptation” refers to changes in the phenotype that are not directly acted on
by natural selection. In the case of the Galápagos finches, the changes in beak size were directly
related to diet; however, as a consequence of that selection, the song pattern was also altered. The
change in song pattern was a byproduct.
Collaborative Questions
1. Discuss how geographical isolation can lead to speciation.
Answer: One of the major driving forces behind speciation is geographical isolation. If a population is
geographically isolated from another population of the same species, then genes will not mix between
these two populations. As a result of this isolation, any mutations or shifts in allele frequency which
occur in one population will be independent of those that occur in the other. As different genetic
changes accumulate in the two populations, they may eventually become reproductively isolated.
2. Evolution can proceed at different rates. Discuss the two models that address the speed at which
evolution occurs.
Answer: Gradualism is when new species evolve slowly and continuously over long periods of time.
Small positive changes in the genotypes and phenotypes of individuals make that individual better
suited for its environment and these changes are passed on to that individual’s offspring. Over time
genotypic and phenotypic changes accumulate and these changes give that species a selective
advantage. Punctuated equilibrium is when the species remain relatively unchanged for long periods of
time followed by a short burst of rapid change. This model was proposed by Steven Jay Gould and
Niles Eldridge. This idea is supported by the fossil record due to the scarcity of transitional forms
between species. In either case, natural selection is the driving force behind these changes.