Self-Assessment Questions

Question 2

“Standing genetic variation”
a. exists before selection acts on a trait.
b. appears after selection has begun to act.
c. helps humans to walk upright.

Answer 2

a

Question 3

A genetic correlation can occur when
a. the same alleles at a locus are favored in different populations.
b. loci are close together on the same chromosome.
c. an allele at one locus is found together with an allele at a second locus more often than by chance.

Answer 3

c

Question 4

Adaptation from “standing genetic variation” involves
a. previously neutral or deleterious alleles becoming advantageous.
b. newly arising alleles sweeping to fixation.
c. selection for an increase in genetic variation.

Answer 4

a

Question 5

True or False? For a neutral allele to spread by hitchhiking with a beneficial allele at another locus, the two loci must be in linkage disequilibrium.
a. True
b. False

Answer 5

a. True

Question 6

Balancing selection
a. occurs when selection coefficients do not change over time.
b. decreases genetic variation.
c. maintains genetic variation.

Answer 6

c. maintains genetic variation.

Question 7

The relative fitnesses of the three genotypes A1A1, A1A2, and A2A2 are W11 = 0.85, W12 = 1, and W22 = 0.65, respectively. How do you expect the population to evolve?
a. The population will become fixed for the A1 allele.
b. The population will become fixed for the A2 allele.
c. The population will evolve to a polymorphic equilibrium at which the frequency of the A2 allele is p = 0.3.

Answer 7

c. The population will evolve to a polymorphic equilibrium at which the frequency of the A2 allele is p = 0.3.

Question 8

If the fitnesses of A1A1, A1A2, and A2A2 are W11 = 1.1, W12 = 1.0, and W22 = 1.5, respectively. We expect that
a. the A1 allele will spread to fixation.
b. the A2 allele will spread to fixation.
c. the A1 allele will spread to fixation if it is common, but the A2 allele will spread to fixation if it is common.
d. The population will evolve to a polymorphic equilibrium at which the frequency of the A2 allele is p = 0.3.

Answer 8

c. the A1 allele will spread to fixation if it is common, but the A2 allele will spread to fixation if it is common.

Question 9

True or False? Positive frequency-dependent selection eliminates genetic variation.
a. True
b. False

Answer 9

a. True

Question 10

In the adaptive landscape, the y-axis shows
a. the allele frequency p.
b. the number of generations for a mutation to spread through the population.
c. the population’s mean fitness (y-axis).

Answer 10

c. the population’s mean fitness (y-axis).

Question 11

According to Fisher’s fundamental theorem,
a. heterozygotes have highest fitness.
b. linkage disequilibrium will evolve towards zero.
c. selection tends to cause a population’s mean fitness to increase.

Answer 11

c. selection tends to cause a population’s mean fitness to increase.

Question 12

True or False? The mean fitness of a population is expected to increase if selection coefficients are constant in time.
a. True
b. False

Answer 12

a. True

Question 13

Mutation load is
a. the weight of new mutations.
b. a heavy metal band.
c. the decrease in a population’s mean fitness caused by deleterious mutations.

Answer 13

c. the decrease in a population’s mean fitness caused by deleterious mutations.

Question 14

A deleterious allele will have higher frequency if
a. the selection coefficient is larger.
b. if the mutation rate is larger.
c. it causes musicians to die at a relatively young age.

Answer 14

b. if the mutation rate is larger.

Question 15

True or False? An allele can only spread in a population if it increases fitness.
a. True
b. False

Answer 15

b. False

Question 16

True or False? In a single generation of random genetic drift, a rare allele will usually become even more rare.
a. True
b. False

Answer 16

b. False

Question 17

True or False? If drift is the only evolutionary force at work, a locus that is variable now will eventually become fixed for one allele or the other.
a. True
b. False

Answer 17

a. True

Question 18

Which of the following situations will cause the nucleotide diversity to decrease in time?
a. The population experiences a sharp decrease in size.
b. The population is growing.
c. The mutation rate increases.

Answer 18

a. The population experiences a sharp decrease in size.

Question 19

True or False? Heterozygosity is on average higher in the native people living in Brazil than those in Ethiopia.
a. True
b. False

Answer 19

b. False

Question 20

A gene tree
a. shows the evolutionary history of a sample of gene copies at a locus.
b. shows how a gene affects a species of tree.
c. is smaller on average when Ne is large.
d. drops its leaves in the fall.

Answer 20

a. shows the evolutionary history of a sample of gene copies at a locus.

Question 21

True or False? The “mitochondrial Eve” was the first human alive on Earth.
a. True
b. False

Answer 21

b. False

Question 22

Genes that experience stronger purifying selection
a. tend to have less genetic variation.
b. are more valuable because they have fewer impurities.
c. evolve more rapidly.

Answer 22

a. tend to have less genetic variation.

Question 23

True or False? Regions of a chromosome that have less recombination tend to have less genetic variation.
a. True
b. False

Answer 23

a. True

Question 24

If one species has much more genetic variation than a second species at the same locus, then the first species
a. is experiencing a selective sweep.
b. has a smaller gene tree.
c. probably has a much larger population size.

Answer 24

c. probably has a much larger population size.

Question 25

The inbreeding load a. is greater in large animals than small animals. b. can cause a population's fitness to decrease to the point that it becomes extinct. c. usually occurs in species with large effective population sizes.

Answer 25

b. can cause a population's fitness to decrease to the point that it becomes extinct.

Question 26

An allele that increases fitness by s = 0.01 is at a frequency of p = 0.5 in a population whose effective size is Ne = 10,000. This allele a. probably spread to its current frequency by drift. b. is going through a peak shift. c. probably will increase in frequency to p = 1.

Answer 26

c. probably will increase in frequency to p = 1.

Question 27

A peak shift can happen when a. underdominant selection is acting. b. the adaptive landscape has a peak at p = 0.5. c. an allele has no effect on fitness.

Answer 27

a. underdominant selection is acting.

Question 28

Would you expect that the biggest differences in the DNA sequence for a hemoglobin gene will be between a. a shark and a whale. b. a mouse and a human. c. a chicken and a sparrow.

Answer 28

a. a shark and a whale.

Question 29

True or False? Pseudogenes are parts of the genome that have no effect on fitness. We therefore expect them to evolve very slowly. a. True b. False

Answer 29

b. False

Question 30

If two species have more nonsynonymous differences than synonymous differences in a particular gene, then that gene a. has different definitions in the two species. b. is under stabilizing selection. c. probably evolved by positive selection.

Answer 30

c. probably evolved by positive selection.

Question 31

If two populations differ much more at one gene than anywhere else in the genome, then that gene a. is evolving as predicted by the neutral theory of molecular evolution. b. may be locally adapted. c. probably has a very high mutation rate.

Answer 31

b. may be locally adapted.

Question 32

True or False? Quantitative traits cannot evolve beyond their original range of variation. a. True b. False

Answer 32

b. False

Question 33

True or False? A trait that is affected by only a single locus with two alleles cannot have a smooth bell-shaped distribution. a. True b. False

Answer 33

b. False

Question 34

A fitness function a. is used to measure muscle tone. b. always has a positive slope. c. shows the average fitness for individuals with different values of a trait.

Answer 34

c. shows the average fitness for individuals with different values of a trait.

Question 35

A selection gradient a. measures the strength of directional selection. b. describes the shape of the adaptive landscape. c. is steeper on the sides than on the tops of mountains.

Answer 35

a. measures the strength of directional selection.

Question 36

Traits evolve more quickly when a. they have more additive genetic variance. b. they have more phenotypic variance. c. they are affected by fewer genes.

Answer 36

a. they have more additive genetic variance.

Question 37

True or False? We expect that most or even all species will be able to avoid extinction by adapting to climate change. a. True b. False

Answer 37

b. False

Question 38

True or False? Overdominance contributes to additive genetic variance. a. True b. False

Answer 38

b. False

Question 39

Compared with small populations, experiments show that when selection acts on larger populations, they tend to evolve a. slower. b. at the same speed. c. faster.

Answer 39

c. faster.

Question 40

The two causes of genetic correlations are (Select all that apply.) a. pleiotropy. b. heritability. c. trade-offs. d. linkage disequilibrium.

Answer 40

b. heritability. d. linkage disequilibrium.

Question 41

For a trait to evolve as an indirect response to selection, which two of these conditions must be met? Select all that apply. a. Selection acts on another trait. b. the selection gradient is negative. c. the trait has a genetic covariance with another trait. d. the trait has either dominance variance or epistatic variance.

Answer 41

a. Selection acts on another trait. c. the trait has a genetic covariance with another trait.

Question 42

True or false? Phenotypic plasticity requires genetic variation. a. True b. False

Answer 42

b. False

Question 43

True or False? All reaction norms are adaptations that increase fitness. a. True b. False

Answer 43

b. False

Question 44

True or False? QTL mapping is not possible in humans because they cannot be bred together in an experiment. a. True b. False

Answer 44

b. False

Question 45

True or false? The loci responsible for genetic variation within a species and for differences between species are usually the same. a. True b. False

Answer 45

b. False

Question 46

A value of FST = 0 means that a. there is no genetic variation in the populations. b. there is no genetic drift in the populations. c. there are no differences in allele frequencies between the populations.

Answer 46

c. there are no differences in allele frequencies between the populations.

Question 47

True or False? Migration between two populations is measured using the migration variance. a. True b. False

Answer 47

b. False

Question 48

True or False? Migration of individuals into a population results in fewer heterozygotes than expected at Hardy-Weinberg equilibrium. a. True b. False

Answer 48

a. True

Question 49

We say that "gene swamping" occurs when a. an adaptive landscape sinks below sea level. b. gene flow is so strong that locally adapted alleles are lost. c. a cline is very steep.

Answer 49

b. gene flow is so strong that locally adapted alleles are lost.

Question 50

Increasing gene flow causes a cline to a. become less steep. b. become more steep. c. become locally adapted.

Answer 50

a. become less steep.

Question 51

True or False? Increasing the migration rate (m) will cause FST between two populations to increase. a. True b. False

Answer 51

b. False

Question 52

Isolation-by-distance is a. a pattern in which genetic differences between populations increases with the distance between them. b. an emotion felt when romantic partners are far from each other. c. a result of high linkage disequilibrium.

Answer 52

a. a pattern in which genetic differences between populations increases with the distance between them.

Question 53

Ecological competition between close relatives can a. favor the evolution of increased dispersal. b. cause individuals to be grumpy. c. cause the origin of a new species.

Answer 53

a. favor the evolution of increased dispersal.

Question 54

True or False? Although the global climate is now rapidly changing, most species are expected to avoid extinction by adapting to the new conditions. a. True b. False

Answer 54

b. False

Question 55

True or False? Some biologists oppose using the biological species concept because it is hard to tell if two kinds of organisms can produce fertile hybrids. a. True b. False

Answer 55

b. False

Question 56

Suppose you are studying malarial transmission. You collect a lot of mosquitoes at a camp site in the Amazonian rain forest, and bring them to a university lab, where you can sequence some DNA from each individual mosquito. What would be the best evidence that you have collected more than one species? a. Different individuals have some DNA differences. b. Individuals that have different DNA sequences of a pigmentation gene also differ in the sequence of some genes that encode various enzymes. c. You find that there are two common alleles of an olfactory receptor gene, and they are in Hardy-Weinberg equilibrium.+

Answer 56

b. Individuals that have different DNA sequences of a pigmentation gene also differ in the sequence of some genes that encode various enzymes.

Question 57

Suppose that a plant species flowers from early June to early July, and its sister species flowers from late July to late August. This is an example of a. prezygotic isolation. b. postzygotic isolation. c. Dobzhansky-Muller incompatibility.

Answer 57

a. prezygotic isolation.

Question 58

Which is an example of Haldane's rule? a. In first-generation hybrids between two species of pheasants, females are nearly sterile, while males are almost fully fertile. b. When Drosophila species A and B are confined together, A females are more willing to mate with B males than B females are to mate with A males. c. Prezygotic isolation between sister species of darter fish generally evolves faster than postzygotic isolation.

Answer 58

a. In first-generation hybrids between two species of pheasants, females are nearly sterile, while males are almost fully fertile.

Question 59

Although there are many species of finches in the many islands of the Galápagos archipelago, a small, remote island (Cocos Island) has only a single finch species, which is distinctly different from the other species. This fact is consistent with which statement? a. Sympatric speciation is unlikely to occur. b. Parapatric speciation is unlikely. c. Allopatric speciation is unlikely.

Answer 59

a. Sympatric speciation is unlikely to occur.

Question 60

Sympatric speciation would be most likely if reproductive isolation were due to differences a. at one locus. b. at a few loci. c. at many loci.

Answer 60

a. at one locus.

Question 61

True or False? The reason there are so many species is that natural selection favors speciation a. True b. False

Answer 61

b. False

Question 62

Ecological speciation means that a. allopatric populations of a species become adapted to different environments. b. reproductive isolation between populations evolves as a side effect of ecologically adaptive genetic divergence. c. speciation is sympatric rather than allopatric.

Answer 62

b. reproductive isolation between populations evolves as a side effect of ecologically adaptive genetic divergence.

Question 63

True or False? Many groups of organisms include groups of cryptic species that are very difficult to distinguish because they look alike. They are evidence that speciation can occur by genetic drift rather than selection. a. True b. False

Answer 63

b. False

Question 64

Genomic islands of speciation are a. allopatric populations that have limited gene flow with each other. b. regions of the genome that are strongly differentiated as the result of random genetic drift. c. regions of the genome where populations or species are strongly differentiated as the result of divergent selection.

Answer 64

c. regions of the genome where populations or species are strongly differentiated as the result of divergent selection.

Question 65

Populations that have evolved partial reproductive isolation may fail to become different species because a. gene flow increases and they merge. b. one of the populations becomes extinct. c. either gene flow increases and they merge or one population becomes extinct.

Answer 65

c. either gene flow increases and they merge or one population becomes extinct.