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CHAPTER 25
Concept check questions (in figure legends)
FIGURE 25.1
Concept check: What does the term “local population” mean?
Answer: A local population is a group of individuals that are more likely to interbreed
with each other compared with more distant populations.
FIGURE 25.2
Concept check: Are polymorphisms common or rare in natural populations?
Answer: Polymorphisms are very common in nearly all natural populations.
FIGURE 25.6
Concept check: In this form of natural selection, explain the meaning of the word
“directional”.
Answer: The word directional means that selection is favoring a particular phenotype.
Selection is moving the population in the direction in which that phenotype will
predominate.
FIGURE 25.8
Concept check: In this example, is directional selection promoting genetic diversity?
Explain.
Answer: No, because directional selection is eliminating individuals that are sensitive to
DDT.
FIGURE 25.9
Concept check: In general, why does stabilizing selection decrease genetic diversity?
Answer: Stabilizing selection decreases genetic diversity because it eliminates
individuals that carry alleles that promote more extreme phenotypes.
FIGURE 25.10
Concept check: Does this form of natural selection favor polymorphism? Explain why or
why not.
Answer: Yes, this selection fosters polymorphism. The fitness values of phenotypes
depend on the environment. Some phenotypes are the fittest in one environment whereas
other phenotypes are the fittest in another environment.
FIGURE 25.12
Concept check: Explain why the HbS allele is prevalent in certain regions even though it
is detrimental in the homozygous condition.
Answer: The HbS allele is an advantage in the heterozygous condition because it confers
resistance to malaria. The heterozygote advantage outweighs the homozygote
disadvantage.
FIGURE 25.13
Concept check: Explain how negative frequency-dependent selection works.
Answer: In negative frequency-dependent selection, the rarer phenotype has a higher
fitness, which improves its reproductive success.
FIGURE 25.16
Concept check: How does population size affect genetic drift?
Answer: Genetic drift tends to have a greater effect in small populations. It can lead to
the rapid loss or fixation of an allele.
FIGURE 25.17
Concept check: What is happening at the bottleneck? Describe the effect of genetic drift
during the bottleneck.
Answer: At the bottleneck, genetic diversity may be lower because there are fewer
individuals. Also, during the time when the bottleneck occurs, genetic drift may promote
the loss of certain alleles and the fixation of other alleles, thereby diminishing genetic
diversity.
FIGURE 25.18
Concept check: How does inbreeding affect the likelihood of expressing recessive traits?
Explain.
Answer: Inbreeding increasing the likelihood of homozygosity, and therefore tends to
increase the likelihood that an individual will exhibit a recessive trait. This occurs
because an individual can inherit both copies of the same allele from a common ancestor.
FIGURE 25.21
Concept check: What are two common applications of DNA fingerprinting?
Answer: DNA fingerprinting is used for identification and for relationship testing.