1. 21
The Evolution of Populations

2. In evolutionary terms, an organism’s fitness is measured by its _____.
stability in the face of environmental change
contribution to the gene pool of the next generation
genetic variability
mutation rate
health
Answer: B
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3. In evolutionary terms, an organism’s fitness is measured by its _____.
stability in the face of environmental change
contribution to the gene pool of the next generation
genetic variability
mutation rate
health
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4. Red short-horned cattle are homozygous for the red allele, white cattle are homozygous for the white allele, and roan cattle are heterozygotes. Population A consists of 36% red, 16% white, and 48% roan cattle. What are the allele frequencies?
red  0.36, white  0.16
red  0.6, white  0.4
red  0.5, white  0.5
Allele frequencies cannot be determined unless the population is in equilibrium.
Answer: B
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5. Red short-horned cattle are homozygous for the red allele, white cattle are homozygous for the white allele, and roan cattle are heterozygotes. Population A consists of 36% red, 16% white, and 48% roan cattle. What are the allele frequencies?
red  0.36, white  0.16
red  0.6, white  0.4
red  0.5, white  0.5
Allele frequencies cannot be determined unless the population is in equilibrium.
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6. Indicate which of the Hardy-Weinberg conditions is being violated in the following example: Some moths on a tree are easier to see due to their lighter color and therefore are eaten by predators more often.
large population size
no mutation
no gene flow
random mating occurring
no selection
Answer: E. The variation in color is allowing some moths to survive more easily than others; therefore, selection is occurring.
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7. Indicate which of the Hardy-Weinberg conditions is being violated in the following example: Some moths on a tree are easier to see due to their lighter color and therefore are eaten by predators more often.
large population size
no mutation
no gene flow
random mating occurring
no selection
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8. Indicate which of the Hardy-Weinberg conditions is being violated in this example: Female sailfin blennies (a fish) tend to choose males with either a large sailfin on top of their heads or the best flicking motion of their sailfin.
large population size
no mutation
no gene flow
random mating occurring
no selection
Answer: D. There is a pattern to the mating that is occurring, making this nonrandom mating.
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9. Indicate which of the Hardy-Weinberg conditions is being violated in this example: Female sailfin blennies (a fish) tend to choose males with either a large sailfin on top of their heads or the best flicking motion of their sailfin.
large population size
no mutation
no gene flow
random mating occurring
no selection
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10. Indicate which of the Hardy-Weinberg conditions is being violated in this example: Due to global warming, a river has dried up, allowing two different rabbit populations, which were isolated before, to mate with one another.
large population size
no mutation
no gene flow
random mating occurring
no selection
Answer: C. When the river was there and the species were isolated, no gene flow was occurring. Now that gene flow can occur, differences between the populations can be reduced.
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11. Indicate which of the Hardy-Weinberg conditions is being violated in this example: Due to global warming, a river has dried up, allowing two different rabbit populations, which were isolated before, to mate with one another.
large population size
no mutation
no gene flow
random mating occurring
no selection
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12. The textbook discusses how the conversion of quality habitat into farmland has greatly depleted the greater prairie chicken populations and, as a result, their genetic diversity. Which of the following occurred in this example?
founder effects
mutation
natural selection
gene flow
bottlenecking
Answer: E. The drastic drop in population size and genetic diversity is causing the greater prairie chicken to undergo a genetic bottleneck.
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13. The textbook discusses how the conversion of quality habitat into farmland has greatly depleted the greater prairie chicken populations and, as a result, their genetic diversity. Which of the following occurred in this example?
founder effects
mutation
natural selection
gene flow
bottlenecking
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14. Indicate what type of selection is occurring in the example here: Due to less snowfall in an area, white mice are predated on more than intermediate- or dark-colored mice.
directional selection
disruptive selection
stabilizing selection
Answer: A. The population is shifting toward the darker colors, moving the bell curve over to the right.
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15. Indicate what type of selection is occurring in the example here: Due to less snowfall in an area, white mice are predated on more than intermediate- or dark-colored mice.
directional selection
disruptive selection
stabilizing selection
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16. Indicate what type of selection is occurring in the example here: During a drought, it was discovered that finches with large beaks and those with small beaks were more successful due to the food sources available.
directional selection
disruptive selection
stabilizing selection
Answer: B. In this example, the extremes are being favored, and the intermediates are not being favored.
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17. Indicate what type of selection is occurring in the example here: During a drought, it was discovered that finches with large beaks and those with small beaks were more successful due to the food sources available.
directional selection
disruptive selection
stabilizing selection
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18. The frequency of cystic fibrosis, a recessive genetic disease, is 1 per 2,500 births among Northern Europeans. Assuming random mating, what is the frequency of carriers?
1/2,500, or about 0.04%
1/50, or about 2%
1/25, or about 4%
The frequency cannot be calculated because selection violates Hardy-Weinberg assumptions.
Answer: C. The frequency of carriers is 2pq. The allele frequency, q, is 1/50 since qq = 1/2,500. P is close to 1. You may want to discuss why option D does not apply.
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19. The frequency of cystic fibrosis, a recessive genetic disease, is 1 per 2,500 births among Northern Europeans. Assuming random mating, what is the frequency of carriers?
1/2,500, or about 0.04%
1/50, or about 2%
1/25, or about 4%
The frequency cannot be calculated because selection violates Hardy-Weinberg assumptions.
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20. Until the 1950s, infants born with cystic fibrosis did not survive longer than a few months. If the frequency of carriers was 4% in the year 1900, what proportion of CF alleles was eliminated in one generation?
100%
50% 4% 2%
 0.1%
Answer: D. The frequency of CF alleles lost from the death of infants with CF is 2/2,500. The frequency of CF alleles present in heterozygotes is 1/25, or 100/2,500. Thus, approximately 2/100, or 2%, of CF alleles are eliminated from the population because the homozygous infants do not survive to have progeny.
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21. Until the 1950s, infants born with cystic fibrosis did not survive longer than a few months. If the frequency of carriers was 4% in the year 1900, what proportion of CF alleles was eliminated in one generation?
100%
50% 4% 2%
 0.1%
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22. A high proportion of the cats on Key West have extra toes (polydactyly). What is the most likely explanation?
high rate of mutation
founder effect
bottleneck effect
directional selection for extra toes
Answer: B. This question asks students to apply an understanding of the different mechanisms of evolution to formulate a hypothesis that explains an actual situation. In this case, history tells us that the so-called Hemingway cats descended from a six-toed cat brought to the island by a ship captain in the 1800s.
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23. A high proportion of the cats on Key West have extra toes (polydactyly). What is the most likely explanation?
high rate of mutation
founder effect
bottleneck effect
directional selection for extra toes
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24. Evolution requires _____ in order to occur.
a large population
heritable variation
nonrandom, differential reproductive success
a long time
Answer: B. applies only to selection. This is a good question to highlight other drivers of evolution.
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25. Evolution requires _____ in order to occur.
a large population
heritable variation
nonrandom, differential reproductive success
a long time
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26. What is the ultimate source of new heritable variation in populations?
sexual reproduction (e.g., independent assortment, recombination, random mating)
gene flow (e.g., immigration/emigration)
selection (e.g., for favorable traits, against deleterious traits)
mutation (e.g., new alleles from errors in replication/recombination)
Answer: D. A, B, and C can all “stir the pot,” but new variation comes from mutation.
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27. What is the ultimate source of new heritable variation in populations?
sexual reproduction (e.g., independent assortment, recombination, random mating)
gene flow (e.g., immigration/emigration)
selection (e.g., for favorable traits, against deleterious traits)
mutation (e.g., new alleles from errors in replication/recombination)
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28. Which of the following is not an example of heritable genetic variation?
a protein translated incorrectly from an mRNA
a base-pair substitution in an exon
a 100-base-pair duplication in an intron
a 3-base-pair deletion in a promoter
Answer: A. This occurs, but is not heritable.
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29. Which of the following is not an example of heritable genetic variation?
a protein translated incorrectly from an mRNA
a base-pair substitution in an exon
a 100-base-pair duplication in an intron
a 3-base-pair deletion in a promoter
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30. Below are listed genotypic frequencies for four populations at the H locus. Which population(s), if any, are at Hardy-Weinberg equilibrium?
Population HH Hh hh A B C D
Answer: D. Although for all populations p = q = 0.5, only population D satisfies f(HH) = p2, f(Hh) = 2pq, and f(hh) = q2. A very useful follow-up exercise is to ask and then demonstrate how long it would take each population to go to HWE given random mating (answer: one generation for any of the populations).
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31. Below are listed genotypic frequencies for four populations at the H locus. Which population(s), if any, are at Hardy-Weinberg equilibrium?
Population HH Hh hh A B C D
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32. Below are listed genotypic frequencies for four populations at the W locus. Which population(s), if any, are at Hardy-Weinberg equilibrium?
Population WW Ww ww A B C D
Answer: A, B, C, D. Although each population has different values for p and q, in each case, the relationships f(WW) = p2, f(Ww) = 2pq, and f(ww) = q2 are satisfied. This question is useful for driving home the point that HWE is independent of any particular values of p and q. Students often have the misconception that these values tend toward 0.5.
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33. Below are listed genotypic frequencies for four populations at the W locus. Which population(s), if any, are at Hardy-Weinberg equilibrium?
Population WW Ww ww A B C D
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34. Allele frequencies for the ABO blood type among North Americans are estimated at f(IA) = 0.27; f(IB) = 0.06; f(i) = Assuming HWE conditions for this locus, what is the expected frequency of blood type O?
0.67
0.134
0.449
1.0
Answer: C. Blood type O = genotype ii. Thus f(ii) = Students may need to be reminded of blood type genetics if this has not been covered recently. Another good question is asking if HW conditions can reasonably apply here.
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35. Allele frequencies for the ABO blood type among North Americans are estimated at f(IA) = 0.27; f(IB) = 0.06; f(i) = Assuming HWE conditions for this locus, what is the expected frequency of blood type O?
0.67
0.134
0.449
1.0
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36. Allele frequencies for the ABO blood type among North Americans are estimated at f(IA) = 0.27; f(IB) = 0.06; f(i) = Assuming HWE conditions for this locus, what is the expected frequency of blood type A?
0.27
0.073
0.362
0.435
Answer: D. Blood type A is IAIA OR IAi. Thus one must ADD and 2 × 0.27 × This is a good exercise for teaching that “and” means multiplying and “or” means adding.
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37. Allele frequencies for the ABO blood type among North Americans are estimated at f(IA) = 0.27; f(IB) = 0.06; f(i) = Assuming HWE conditions for this locus, what is the expected frequency of blood type A?
0.27
0.073
0.362
0.435
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38. In some regions where malaria is endemic, the frequency of the sickle-cell allele is maintained as high as 10% due to heterozygous advantage. If modern technology were to completely eradicate malaria but not alleviate sickle-cell disease, what would be expected to happen to the sickle-cell allele frequency in subsequent generations?
remain near 10%
gradually drop toward zero
drop slightly, then restabilize
rise slightly, then restabilize
Answer: B. The heterozygous advantage is removed, leaving only strong selection against the allele. Eventually, the frequency would be balanced out only by new mutation (at a very low level).
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39. In some regions where malaria is endemic, the frequency of the sickle-cell allele is maintained as high as 10% due to heterozygous advantage. If modern technology were to completely eradicate malaria but not alleviate sickle-cell disease, what would be expected to happen to the sickle-cell allele frequency in subsequent generations?
remain near 10%
gradually drop toward zero
drop slightly, then restabilize
rise slightly, then restabilize
© 2017 Pearson Education, Ltd.