1. The Evolution of Populations21
The Evolution of Populations
Questions prepared by
Fleur Ferro, Community College of Denver
William Wischusen, Louisiana State University
Ronald Balsamo, Villanova University

2. stability in the face of environmental change
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

3. stability in the face of environmental change
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 3

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 4

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. 5

6. random mating occurring no selection
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. 6

7. random mating occurring no selection
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 7

8. random mating occurring no selection
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. 8

9. random mating occurring no selection
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 9

10. random mating occurring no selection
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 to mate with one another, whereas they were isolated before.
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 happen, this can reduce differences between the populations. 10

11. random mating occurring no selection
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 to mate with one another, whereas they were isolated before.
large population size
no mutation
no gene flow
random mating occurring
no selection 11

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. 12

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 13

14. directional selection disruptive selection stabilizing selection
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. 14

15. directional selection disruptive selection stabilizing selection
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 15

16. directional selection disruptive selection stabilizing selection
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 during the drought.
directional selection
disruptive selection
stabilizing selection
Answer: B
The extremes are being favored in this example, and the intermediates are not being favored. 16

17. directional selection disruptive selection stabilizing selection
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 during the drought.
directional selection
disruptive selection
stabilizing selection 17

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. 18

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. 19

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. 20

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% 21

22. Before treatment with 3TC, did 3TC-resistant viruses exist in these patients?
Answer: A
This question explores the origin of hereditary variation and the dynamics of evolutionary change in populations as a result of selection.
yes no
no way to tell 22

23. Before treatment with 3TC, did 3TC-resistant viruses exist in these patients?
yes no
no way to tell 23

24. directional selection for extra toes
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. 24

25. directional selection for extra toes
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 25