Deck 6: The Ways of Change: Drift and Selection

Question 1

Inbreeding

A) increases heterozygosity in populations.
B) creates deleterious recessive alleles.
C) increases homozygosity in populations.
D) all of the above
E) b and c

Answer 1

C

Question 2

Over the same landscape, populations may differ in degree of subdivision depending on their movement. Which of the following is/are true?

A) Species that move widely across a landscape will show increased genetic divergence with increasing geographic distance.
B) Species that move widely across a landscape will have minimal genetic divergence.
C) Species that do not move widely across a landscape have minimal genetic divergence.
D) a and c
E) b and c

Answer 2

B

Question 3

In the Hardy-Weinberg equation, what does 2pq refer to?

A) the frequency of heterozygotes in a population
B) the frequency of both alleles in a population
C) the frequency of homozygotes in a population
D) none of the above

Answer 3

A

Question 4

A mosquito that has the genotype Ester¹Ester¹ is considered ____ and is ____ at the esterase locus.

A) homozygous dominant; diploid
B) heterozygous; haploid
C) homozygous; diploid
D) heterozygous; diploid

Question 5

The probability of an allele being lost during a genetic bottleneck depends on

A) the beginning frequency of that allele in the population.
B) the severity of the bottleneck.
C) the size of the population before the bottlenecking event.
D) a and b
E) a, b, and c

Question 6

Many plant species are hermaphroditic and run the risk of self-mating. Some species carry self-incompatibility alleles that can prevent this from occurring. If a pollen grain with self-incompatibility allele S₁ lands on a stigma that also carries the S₁ allele, the pollen will not germinate and fertilization does not occur. Thus, this mechanism not only prevents selfing, but also has the unfortunate effect of preventing mating with any other plant that carries the same allele. However, if the pollen lands on a stigma of a plant with a different allele, fertilization occurs. Imagine a population of plants in which the allele frequency of S₁ = 0.9 and the allele frequency of S₂ = 0.1. All other things being equal, individuals with the ____ allele will have higher fitness on average. This is an example of ______.

A) S₁; positive selection
B) S₂; positive selection
C) S₁; negative frequency-dependent selection
D) S_2; negative frequency-dependent selection

Question 7

Which of the following is not an assumption of the Hardy-Weinberg theorem?

A) The population is infinitely large.
B) There is no selection in the population.
C) There is no immigration, but individuals can emigrate out of a population.
D) There are no mutations.

Question 8

If p = 0.8, what is the frequency of heterozygotes in a population, assuming Hardy-Weinberg equilibrium?

A) 0.2
B) 0.64
C) 0.16
D) 0.32
E) none of the above

Question 9

How is a null hypothesis useful in studying how allele frequencies change?

A) It serves as a baseline for change.
B) It explains what happens when there is no change.
C) It explains what happens when there is change.
D) a and b
E) a and c

Question 10

Assuming that a deleterious allele is maintained in a population by mutation-selection balance, which scenario below describes the case where you would expect the equilibrium frequency of the allele to be highest?

A) The mutation rate is low; the allele is highly deleterious.
B) The mutation rate is low; the allele is slightly deleterious.
C) The mutation rate is high; the allele is highly deleterious.
D) The mutation rate is high; the allele is slightly deleterious.

Question 11

Which of the following is not true about a fixed genetic locus?

A) All members of a population carry the same allele for that locus.
B) There is no genetic variation for that locus.
C) All alternative alleles for that locus have disappeared.
D) all of the above
E) none of the above

Question 12

In comparison with genetic drift, evolution by natural selection is

A) random.
B) adaptive.
C) random and adaptive.
D) nonrandom and adaptive.

Question 13

Tasmanian devils once inhabited most of present-day Australia, but only an isolated population on the island of Tasmania has survived to the present day. Which of the following processes has likely affected Tasmanian devils as a result of this history?

A) a higher mutation rate
B) stronger natural selection
C) a genetic bottleneck
D) gene flow

Question 14

Which of the following is an example of the founder effect?

A) Northern elephant seals were hunted to near extinction, but populations later rebounded.
B) A plant seed established a new population after hitching a ride on a migratory bird.
C) A late frost killed 95% of a local population of spring ephemeral plants.
D) all of the above
E) none of the above

Question 15

Alleles are

A) found at genetic loci.
B) always dominant or recessive.
C) alternative forms of a phenotype.
D) a and b
E) a, b, and c

Question 16

The graph below shows the change in allele frequency for a beneficial allele over time (the x axis shows generations). Based on the shape of the curve, this allele is most likely

A) homozygous.
B) dominant.
C) recessive.
D) heterozygous.
E) additive.

Question 17

Why was Charles II of Spain, of the Hapsburg dynasty, called el hechizado, the "hexed"?

A) He could never win a war.
B) It was believed that his ill health was a product of sorcery.
C) He was the offspring of inbreeding.
D) all of the above

Question 18

A genetic bottleneck occurs when

A) there is a temporary dip in population size.
B) a population is very small.
C) a few individuals begin a new isolated population.
D) a and b
E) all of the above

Question 19

Although the Ester¹ allele confers a selective advantage to mosquitoes exposed to DDT on the coast of France, carriers of Ester¹ in inland populations are more likely to be caught by spiders and other predators. This is an example of

A) positive selection.
B) antagonistic pleiotropy.
C) genetic drift.
D) average excess of fitness.
E) none of the above

Question 20

In a population of butterflies that has two alleles at a locus for spots, no spots (N) and spots (S), there are 20 individuals with the NN genotype, 40 with the NS genotype, and 40 with the SS genotype. What is the frequency of N in the population?

A) 0.4
B) 0.2
C) 0.6
D) 0.8
E) none of the above

Question 21

If a population is in Hardy-Weinberg equilibrium and the frequency of homozygous recessive individuals is 0.49, what is the frequency of the recessive allele?

A) 0.51
B) 0.49
C) 0.7
D) 0.3
E) none of the above

Question 22

Lively and Dybdahl studied parasite infection rates in a population of asexual clonal snails. The graph below shows relative infection rates for the four most common clone genotypes and for several rare genotypes (all lumped together). Based on these data, they hypothesized that parasites adapted to infecting the most common clone genotypes in the population, and thus these genotypes had lower fitness. This is consistent with ________ operating in the population. Further evidence would be provided if ________.

A) genetic drift; heterozygosity declined over time in the population
B) genetic drift; rare clones were lost from the population frequency-dependent selection
C) negative frequency-dependent selection; rare clones became common in the next generation but then declined in frequency in the following generation
D) negative frequency-dependent selection; rare clones became more common until they completely replaced the clones that were originally common

Question 23

The sickle-cell anemia allele, S, experiences strong negative selection because of its deleterious effect on homozygotes, yet the allele is maintained at frequencies higher than expected because having only one copy can increase survival in areas where malaria is prevalent. This is an example of

A) heterozygote advantage.
B) antagonistic pleiotropy.
C) balancing selection.
D) a and c
E) a, b, and c

Question 24

In the Hardy-Weinberg equation, p² is

A) an allele frequency.
B) the frequency of heterozygotes.
C) the frequency of dominant alleles.
D) a and c
E) none of the above

Question 25

The effectiveness of selection on an allele depends in part on

A) the frequency of the allele.
B) the magnitude of average excess fitness.
C) the average fitness of the population.
D) all of the above
E) none of the above

Question 26

In the founder effect,

A) allele frequencies always deviate from the parental population.
B) drift only acts on the founding population when it breaks off from the parental population.
C) drift may continue to act on a fledgling population.
D) a and b
E) a and c

Question 27

Genetic drift

A) will always lead to higher fitness of individuals in the population.
B) reduces genetic variation within a population.
C) can lead to divergence between populations.
D) b and c
E) a, b, and c

Question 28

How did Buri's experiments illustrate populations deviating from the assumptions of Hardy-Weinberg equilibrium?

A) Each population started with only eight males and eight females.
B) Reproducing flies were chosen at random.
C) Populations of flies were kept isolated in their own vials.
D) all of the above
E) none of the above

Question 29

Bighorn sheep occupy a range that extends from Canada to Mexico; however, this range is not continuous because the sheep prefer steep rocky cliffs, which are often spatially isolated. This is an example of

A) population structure.
B) population genetics.
C) allopatry.
D) genetic distance.

Question 30

Inbreeding

A) changes allele frequencies in a population.
B) rearranges allele combinations in a population.
C) is a mechanism of evolution.
D) all of the above

Question 31

Which of the following is/are correct regarding the different types of alleles?

A) Additive alleles yield the same effect regardless of the number of alleles present.
B) Dominant alleles yield the same effect regardless of the number of alleles present.
C) Recessive alleles yield the same effect regardless of the number of alleles present.
D) a and c
E) a, b, and c

Question 32

Which of the following is true regarding the relative importance of drift and selection?

A) Populations are large and well mixed, so natural selection is more important.
B) Populations are networks of small groups that occasionally exchange alleles, so genetic drift is more important.
C) Most of the molecular variation in genomes does not influence phenotypes, so genetic drift is more important.
D) none of the above; scientists continue to debate the relative importance of drift and selection

Question 33

Which of the following is the best evidence for a genetic bottleneck in northern elephant seals?

A) They were nearly hunted to extinction.
B) They have low genetic variation within a mitochondrial DNA sequence that has a high mutation rate.
C) Their populations rebounded.
D) all of the above

Question 34

In the Hardy-Weinberg equation, q is

A) an allele frequency.
B) the frequency of heterozygotes.
C) the frequency of dominant alleles.
D) a and c
E) none of the above

Question 35

The study of allele frequencies and distributions is

A) population genetics.
B) community dynamics.
C) biogeography.
D) landscape ecology.

Question 36

Which of the following would be a useful proxy for fitness?

A) probability of survival to reproductive age
B) number of offspring produced by an individual during a specific season
C) probability of survival of offspring
D) a and b
E) a, b, and c

Question 37

The frequency of a slightly deleterious allele maintained at an equilibrium frequency by mutation-selection balance would be higher

A) if the mutation rate is high.
B) if the mutation rate is low.
C) if the selection coefficient is high.
D) if the population size is small.

Question 38

An example of a phenotype is _____, while a genotype would be _____.

A) homozygous; Ester¹Ester¹
B) heterozygous; EsterEster
C) esterase production; Ester¹Ester
D) esterase production; Ester¹

Question 39

In a population of infinite size, which statement accurately describes the eventual fate of a new beneficial allele?

A) If it is dominant, it will reach fixation; if it is recessive, it will rise to high frequency but not reach fixation.
B) If it is dominant it will rise to high frequency but will not reach fixation; if it is recessive, it will reach fixation.
C) Since it is advantageous, it will reach fixation regardless of whether it is dominant or recessive.
D) Regardless of whether it is dominant or recessive, it will rise to high frequency but not reach fixation.

Question 40

Which of the following scientific disciplines does not fall under the purview of landscape genetics?

A) landscape ecology
B) spatial statistics
C) population genetics
D) community dynamics

Question 41

How does "random mating" affect population genetics studies?

A) Random mating only relates to the locus of interest, so sexual selection often does not affect population genetics studies.
B) Individuals never have a strong mate preference, so they frequently mate with any "random" individual.
C) Individuals always have a strong mate preference, so population genetics studies are almost always biased.
D) none of the above

Question 42

Mutations in the GDF9 gene in sheep have been linked to changes in female fecundity. The following are the relative fitnesses of different genotypes in the population. Which statement below is correct?
Genotype Relative fitness
+/ -           1
+/ +           0.7
-/ -           0.1

A) This is an example of heterozygote advantage; genetic variation will be maintained over time.
B) This is an example of negative frequency-dependent selection; genetic variation will be maintained over time.
C) This is an example of heterozygote advantage; genetic variation will be lost over time.
D) This is an example of negative frequency-dependent selection; genetic variation will be lost over time.

Question 43

A bowl of beads has 500 red and 500 white beads. In a random sample of two beads, you select two white beads; if you took a random sample of 100 beads, you would expect

A) mostly white beads again because it is obviously easier to draw white beads.
B) mostly red beads this time; it is actually easier to draw red beads.
C) approximately 50 red beads and 50 white beads because it is a larger sample.
D) none of the above; there is not enough information given to make a prediction.

Question 44

Genetic drift

A) reduces genetic variation within a population.
B) increases divergence (variation) between populations.
C) affects only neutral alleles.
D) a and b
E) a, b, and c

Question 45

Discuss the effectiveness of genetic drift and natural selection in small versus large populations. Please be sure to explain why each process is stronger or weaker depending on the population size.

Question 46

Inbreeding results in a higher frequency of ________ in a population. Inbreeding depression occurs because _______.

A) deleterious alleles; individuals with deleterious alleles have high mortality
B) heterozygosity; heterozygotes have lower fitness
C) homozygosity; deleterious recessive alleles are expressed more often
D) heterozygosity; deleterious dominant alleles are expressed more often

Question 47

Which of the following would likely increase the likelihood of fixing a beneficial allele in a population of finite size?

A) a higher starting frequency to decrease likelihood of drift
B) a larger excess fitness to increase selection for the beneficial allele
C) a larger population size because selection will be greater in a larger population
D) all of the above
E) none of the above

Question 48

How might population structure affect evolution?

A) increases the opportunity for selection to change allele frequencies
B) decreases the opportunity for selection to change allele frequencies
C) increases the opportunity for drift to change allele frequencies
D) decreases the opportunity for drift to change allele frequencies

Question 49

Which of the following statements is/are supported by the figure?

A) In 1973 the Ester¹ allele was less widespread than in 1975 or 1978.
B) The Ester¹ allele was fixed in coastal populations by 1975.
C) In 1973 the Ester¹ allele did not exist 21 km inland.
D) all of the above

Question 50

In which of the scenarios below is a population more likely to evolve?

A) a population that experiences no migration
B) a population that is large enough to not experience genetic drift
C) a population where there are no adaptive traits
D) a population that experiences a mutation in a gene necessary for survival

Question 51

Which of the following is/are true regarding genetic distance among populations?

A) Genetic distance increases as the time populations are separated increases.
B) Genetic distance increases faster in smaller populations.
C) Genetic distance increases faster in larger populations.
D) a and b
E) a and c

Question 52

How do gene frequencies behave in Hardy-Weinberg equilibrium?

A) Allele frequencies stay the same from generation to generation.
B) Genotype frequencies stay the same from generation to generation.
C) Genotype frequencies depart from expected frequencies.
D) a and b
E) a, b, and c

Question 53

Please describe two factors that would increase the likelihood of fixing a beneficial allele in a population of finite size.

Question 54

In a population of ground beetles, a genetic locus that codes for setae on the elytra has two variants: G is dominant and codes for setae on the elytra, and g is recessive and codes for glabrous elytra (no setae). If the frequency of beetles with glabrous elytra is 0.36, what is the frequency of the G allele, assuming the population is in Hardy-Weinberg equilibrium?

A) 0.6
B) 0.4
C) 0.64
D) 0.16
E) none of the above

Question 55

The graphs below show the results of simulations of the effect of selection on deleterious alleles. Population size is infinite in both simulations, and the starting frequency and the strength of selection are the same. (a) Based on the shape of the curves, why do the results of the simulations differ? Explain your answer.
(b) The allele in the second simulation is not eliminated entirely from the population. Would this change if the population was finite in size? Why or why not?

Question 56

The graph below depicts the change in frequency for an advantageous allele in two different populations, both of infinite size. The strength of selection is the same in both populations. (a) What type of allele is this? Explain how you know.
(b) Why does the frequency of the allele in one of the populations rise faster than the frequency in the other population?
(c) If given enough time, will the allele become fixed in each of these populations?

Question 57

You collect the following data on genotypes for a sunflower population: AA: 40, AB: 20, BB: 40. Based on Hardy-Weinberg predictions you expected the following numbers: AA: 25, AB: 50, BB: 25. Which of the following is a plausible explanation for the deviation?

A) balancing selection
B) negative frequency-dependent selection
C) inbreeding
D) genetic drift

Question 58

When F_ST ≈ 0, a population

A) has little genetic structure.
B) has extensive spatial variation.
C) consists mostly of homozygotes.
D) a and b
E) a and c

Question 59

The graph below shows results of two simulations, both depicting the rise in frequency of a beneficial allele in a population of infinite size. The selection coefficient and the starting frequency are the same, but in one simulation the beneficial allele is dominant and in the other it is recessive. Neither allele is fixed by 500 generations. (a) Which simulation shows results for a dominant and which shows results for a recessive allele? How can you tell?
(b) Neither of the alleles reaches fixation by 500 generations. If given enough time, will both of these alleles reach fixation in the population? Why or why not?

Question 60

Some Drosophila melanogaster larvae use a "sitting" foraging strategy in which they feed more or less in the same location, while "rovers" wander around the substrate looking for more food sources. In the graph below, the dotted line corresponds to sitters and the solid line corresponds to rovers. This is an example of _______; over time we expect ________.

A) negative frequency-dependent selection; both strategies to persist in the population
B) pleiotropy; both strategies to persist in the population
C) frequency-dependent selection; the rover strategy to replace the sitter strategy because it has the highest fitness
D) pleiotropy; the rover strategy to replace the sitter strategy because it has the highest fitness

Question 61

A researcher performs an experiment on fruit flies to monitor the change in allele frequency of an allele called
A. She starts with 24 populations, each with an initial starting frequency for A of 0.5. Flies are maintained for ten generations by transferring the offspring from each generation to a new vial, where they produce the next generation. For half of the populations she randomly selects 20 flies to transfer, while for the other half she randomly selects 200 flies to transfer. After ten generations she collects the following allele frequency data:
​
Treatment 1: 0.55, 0.6, 0.2, 0.9, 0.45, 0.35, 0.1, 0.65, 0.65. 0.55, 0.75, 0.35
Treatment 2: 0.85, 0.8, 0.75, 0.8, 0.75, 1.0, 0.8, 0.85, 0.9, 0.8, 0.85, 0.8
​
What is a plausible explanation for the differences between the treatments? Please make sure to explain your logic.

Question 62

Contrast evolution by natural selection with evolution by genetic drift.

Question 63

Considering the principles of mutation, natural selection, and genetic drift, do you expect adaptive evolution to occur more rapidly in small or large populations? What about nonadaptive evolution? For each answer, please explain your reasoning.

Question 64

Explain how landscape genetics can influence the evolution of populations.

Question 65

Earth's biotic and abiotic environments are changing rapidly due, in part, to human activities. For example, the introduction of non-native invasive species into new habitats and climate change highlight two ways in which humans are altering the environment experienced by other species. Some species will probably adapt to these changes, while others may not. Considering the processes of mutation, natural selection, and genetic drift, comment on the likelihood of adaptation to environmental change for species that have small population sizes versus species with large population sizes. At a minimum, a fully correct answer will incorporate all three of these processes into the answer.

Question 66

You are studying a population of 100 flowers that has two alleles at a locus for flower color, blue (B) and green (G). There are 15 individuals with the BB genotype, 70 individuals with the BG genotype, and 15 individuals with the GG genotype.
(a) What are the allele frequencies of B and G in the starting population? Show your calculations.
(b) Is this population in Hardy-Weinberg equilibrium? Show your calculations.
(c) Given the results of part b and the distribution of genotypes, offer a hypothesis that could explain the results. Explain your reasoning.

Question 67

Below you see graphs that depict the change in frequency of a neutral allele in four populations that differ in size. Which population would you predict is the smallest?

Question 68

Why might an endangered species, whose population numbers are already low, be even more threatened to extinction because of inbreeding?

Question 69

Explain the four assumptions of the Hardy-Weinberg theorem.

Question 70

Compare two examples of genetic drift: the genetic bottleneck and the founder effect.

Question 71

The graph below depicts the rise in resistance to warfarin in a rat population. Notice that after reaching a peak of 100% resistance, resistance in the population declined. Please provide a plausible evolutionary explanation for this.