Ch 10 Genetic Drift

Front 1

A great deal of evolutionary change happens “by chance alone” and serves absolutely no purpose.
A. true B. false

Back 1

A. true

Front 2

Scientists use the concept of randomness to do which of these?
A. predict sex ratios
B. predict allele frequencies in future generations
C. predict phenotype frequencies in future generations
D. calculate expected frequencies
E. all of these

Back 2

E. all of these

Front 3

Random fluctuations in allele frequencies through time can be the result of simple sampling error in producing offspring genotypes.
A. true B. false

Back 3

A. true

Front 4

Which of these population sizes would be most strongly influenced by genetic drift?
A. 10 B. 20 C. 100 D. 200 E. 500

Back 4

A. 10

Front 5

Which of these population sizes would be least strongly influenced by genetic drift?
A. 10 B. 20 C. 100 D. 200 E. 500

Back 5

E. 500

Front 6

The idea that all current gene copies in a population can be traced back in time to a single ancestor is called which of these?
A. genetic drift
B. Natural Selection
C. coalescence theory
D. neutral evolution
E. Markov chain simulation

Back 6

C. coalescence theory

Front 7

How many gene copies for gene A are present in a current population consists of 100 randomly mating diploid individuals?
A. 100 B. 200 C. 1 D. 2 E. 500

Back 7

B. 200

Front 8

One individual in the population of the previous question (individual #26) has two A alleles A1 and A2. What is the chance that the A1 allele from #26 becomes the only copy in a future generation due to chance alone?
A. 0.5 B. 0 C. 1 D. 1/100 E. 1/200

Back 8

E. 1/200

Front 9

Which of these is a semi-isolated subpopulation of any organism?
A. population
B. metapopulation
C. synod
D. deme
E. none of these

Back 9

D. deme

Front 10

Which of these is the sum total of all semi-isolated subpopulations?
A. population
B. metapopulation
C. synod
D. deme
E. none of these

Back 10

B. metapopulation

Front 11

What is the average number of generations required for fixation of a newly arisen mutant allele in a population of N individuals?
A. N B. 2N C. 3N D. 4N E. N!

Back 11

D. 4N

Front 12

The data presented in the figure above refer to the fates of 107 small populations (N=16) started with P=5 for the bw75 allele. Early generations of this experiment revealed which of these with respect to this allele and the starting population?
A. Frequency of bw75 alleles became much more variable.
B. Frequency of bw75 alleles became much less variable.
C. Frequency of bw75 alleles became constant.
D. Allele bw75 alleles became fixed in all populations.
E. Allele bw75 alleles were lost in all populations.

Back 12

A. Frequency of bw75 alleles became much more variable.

Front 13

How many populations became fixed for a single allele by the 19th generation of the experiment illustrated above?
A. none B. all C. 30 D. 28 E. 58

Back 13

E. 58

Front 14

If this experiment were continued for many generations, how many populations would become fixed for a single allele?
A. all B. none C. 50% D. 25% E. 75%

Back 14

A. all

Front 15

What is the only evolutionary phenomenon involved in this experiment?
A. natural selection
B. genetic drift
C. gene flow
D. sexual selection
E. kin selection

Back 15

B. genetic drift

Front 16

Doubling the population size in this experiment would have what effect on the outcome?
A. Decrease number of populations fixed for a single allele.
B. Increase number of populations fixed for a single allele.
C. Decrease frequency of bw75
D. Increase frequency of bw75
E. none of these

Back 16

A. Decrease number of populations fixed for a single allele.

Front 17

The data presented above indicate which of these?
A. Genetic fixation in small populations
B. Increasing heterozygosity (H) as population size increases.
C. Decreasing homozygosity (H) as population size increases.
D. considerable variation among populations
E. all of these

Back 17

E. all of these

Front 18

How many trial populations in the experiment shown in the figure above became fixed for the dominant allele? A. 6 B. 7 C. 5 D. 8 E. 0

Back 18

B. 7

Front 19

How many trial populations in the experiment shown in the figure above became fixed for the recessive allele? A. 6 B. 7 C. 5 D. 8 E. 0

Back 19

C. 5

Front 20

How many trial populations in the experiment shown in the figure remained polymorphic for these alleles? A. 6 B. 7 C. 5 D. 8 E. 0

Back 20

D. 8

Front 21

If this experiment were repeated (replicated) many times, some experimental populations would become fixed for each allele in almost every replicate.
A. true B. false

Back 21

A. true

Front 22

If this experiment were replicated 100 times with an average of 12 fixations, what is the BEST estimate of the number that will be fixed in trial 101?
A. 0 B. 12 C. 22 D. 4 E. all

Back 22

B. 12

Front 23

A novel mutation which occurs in a population of 100 randomly breeding diploid individuals has what chance of becoming fixed in the population through time?
A. 0.5 B. 0 C. 1 D. 1/100 E. 1/200

Back 23

E. 1/200

Front 24

What is the average time for fixation for every mutation which does become fixed in the previous populations?
A. 100 generations
B. 200 generations
C. 400 generations
D. 1000 generations
E. 4 generations

Back 24

A. 100 generations

Front 25

What is the value for average time to fixation for any population size N?
A. N B. 2N C. 4N D. N2 E. no way to know

Back 25

C. 4N

Front 26

Allele frequencies will change because of genetic drift most rapidly in which of these populations?
A. 10 B. 20 C. 100 D. 200 E. 500

Back 26

A. 10

Front 27

Allele frequencies will change because of genetic drift most slowly in which of these populations?
A. 10 B. 20 C. 100 D. 200 E. 500

Back 27

E. 500

Front 28

Which sex contributes the most genes to successive generations in the northern elephant seal, Mirounga angustirostris?
A. males B. females C. neither

Back 28

C. neither

Front 29

Which of these describe the effective populations size (Ne) of northern elephant seal, Mirounga angustirostris relative to census counts for a population (N)?
A. Ne =N B. Ne>N C. Ne>>N D. N> Ne E. N>> Ne

Back 29

E. N>> Ne

Front 30

Which of these is most appropriate for estimating Ne if population sizes varies considerably from generations to generation?
A. average or mean of the N’s
B. harmonic mean of N’s
C. minimal N
D. maximal N
E. none of these

Back 30

B. harmonic mean of N’s

Front 31

For the 65 different populations reported in the figure above, the median (= halfway point in the distribution) for the ratio Ne /N is at which of these values?
A. 0.05 B. 0.10 C. 0.15 D. 0.20 E. 0.25

Back 31

C. 0.15

Front 32

What is the average value of Ne /N for these 65 populations?
A. 0.05-0.10 B. 0.10-0.15 C. 0.15-0.20 D. 0.20-0.25 E. 0

Back 32

B. 0.10-0.15

Front 33

Atlantic codfish used to supply most of the fish sticks to the world; but they are now commercially extinct in the North Atlantic fishery. Each adult female can produce several million eggs per season, but the surviving populations seem to be suffering the negative effects of genetic drift. Which of these is probably the better estimate of Ne for the Atlantic codfish?
A. total number of fish, regardless of age
B. total number of fish after the planktonic larval stage
C. total number of adult fish
D. number of adult females only
E. 42

Back 33

C. total number of adult fish

Front 34

High reproductive rate decreases the time necessary for recovery from a bottleneck event.
A. true B. false

Back 34

B. false

Front 35

Genetic drift in small populations results in reduced genetic diversity and heterozygosity.
A. true B. false

Back 35

A. true

Front 36

Two alleles (A and B) segregate at a locus. Assuming that no stabilizing forces exist, the A allele will eventually be
a. fixed.
b. lost or found.
c. preserved.
d. fixed or broken.
e. either lost or fixed.

Back 36

e. either lost or fixed.

Front 37

Refer to the figure below. A set of 107 experimental populations of Drosophila melanogaster were maintained at a population size of 16 individuals for multiple generations. In each population, the initial frequencies of bw75 and bw alleles were equal. After 19 generations, the bw75 was fixed in 28 populations and lost in 30 populations. These results suggest that
a. both alleles are neutral, and fixation events were due to genetic drift.
b. the bw75 allele has a higher fitness than the bw allele, and fixation events were due to genetic drift.
c. the bw75 allele has a higher fitness than the bw allele, and fixation events were due to natural selection.
d. both alleles are neutral, and fixation events were due to natural selection.
e. a population size of 16 individuals is too small to display the effects of genetic drift.

Back 37

a. both alleles are neutral, and fixation events were due to genetic drift.

Front 38

Refer to the figure below. Rates of synonymous and nonsynonymous substitutions differ for different mammalian lineages. How does this difference affect the relative validity of the neutral theory (as opposed to selectionist explanations)?
a. The data can be understood only in terms of neutral evolution.
b. The data can be understood only in terms of natural selection.
c. Both lineage-specific patterns of natural selection and lineage-specific differences in effective population size can produce the observed patterns (the net effect being equivocal).
d. Natural selection seems to affect only synonymous changes.
e. The neutral theory is applicable only to the primate lineage.

Back 38

c. Both lineage-specific patterns of natural selection and lineage-specific differences in effective population size can produce the observed patterns (the net effect being equivocal).

Front 39

In the late eighteenth century a typhoon swept through the Pacific atoll of Pingelap, leaving approximately 20 survivors. A large percentage of the present-day inhabitants of Pingelap are color blind. The population in question went through a
a. coalescence.
b. speciation event.
c. selective sweep.
d. bottleneck.
e. mutation.

Back 39

d. bottleneck.

Front 40

FST is a measure of population differentiation. An equation exists for the equilibrium FST when the forces of drift and mutation counteract each other. Which of the following statements is false?
a. If rates of migration are high, then at equilibrium FST will be low.
b. Gene flow causes demes to differ, while genetic drift causes demes to be similar.
c. FST levels can be used to estimate migration rates.
d. If rates of migration are low, then at equilibrium FST will be high.
e. If population sizes are large, FST will be low.

Back 40

b. Gene flow causes demes to differ, while genetic drift causes demes to be similar.

Front 41

Which of the following is not a reason that effective population size can be smaller than the actual population size?
a. Different numbers of males and females are present.
b. Every individual produces exactly two offspring.
c. Overlapping generations exist.
d. Natural selection occurs (high variance in the number of offspring).
e. Fluctuations in population size occur.

Back 41

b. Every individual produces exactly two offspring.

Front 42

Consider a hypothetical locus with two segregating alleles (A and B). Population size is small, mutation is absent, and neither of the two alleles has a selective advantage. After a long period of time (many generations), what will occur?
a. Allele frequencies will change over time, but both alleles will remain.
b. Allele frequencies will remain constant.
c. Balancing selection will maintain both alleles.
d. Allele frequencies will cycle over time.
e. The population will eventually become monomorphic for one of the two alleles.

Back 42

e. The population will eventually become monomorphic for one of the two alleles.

Front 43

What is the reasoning behind the McDonald-Kreitman test?
a. Synonymous sites are under greater constraint than nonsynonymous sites.
b. Mutation rates do not affect polymorphism levels.
c. If neutrality holds, there should be a positive correlation between the heterozygosity at a locus and its rate of evolution (rate of substitution).
d. If neutrality holds, polymorphism and substitution data should be uncorrelated.
e. Population size does not affect levels of polymorphism.

Back 43

c. If neutrality holds, there should be a positive correlation between the heterozygosity at a locus and its rate of evolution (rate of substitution).

Front 44

Very little genetic variation exists for populations of the northern elephant seal (Mirounga angustirostris). While 30,000 individuals exist today, in the 1890s hunting reduced the population size to about 20 individuals. What effect did this have?
a. Per nucleotide mutation rates were increased.
b. The effective population size is higher because hunting selected for clever seals.
c. The effective population size is low because of a population bottleneck.
d. Hunting did not affect the genetic diversity.
e. Per nucleotide mutation rates were decreased.

Back 44

c. The effective population size is low because of a population bottleneck.

Front 45

A striking conclusion of the neutral theory is that the rate of fixation of neutral mutations is equal to the mutation rate (u0). Why is this so?
a. Different allele copies have different probabilities of fixation.
b. Mutation rates are orders of magnitude larger than other parameters in evolutionary biology.
c. Genetic drift does not affect the probability of fixation.
d. The number of new mutations in a population per generation, multiplied by the probability that any one allele copy will be fixed, is equal to u0.
e. Functional constraints do not affect the rate of evolution.

Back 45

d. The number of new mutations in a population per generation, multiplied by the probability that any one allele copy will be fixed, is equal to u0.

Front 46

Which of the following ideas does not underlie Kimura’s neutral theory of molecular evolution?
a. High amounts of genetic variation segregate in natural populations.
b. Evolutionary changes at the molecular level occur at a relatively constant rate.
c. Advantageous mutations occur often, and many fixation events are due to positive selection.
d. Mutation rates affect rates of substitution.
e. Deleterious alleles are eliminated by means of (purifying) natural selection.

Back 46

c. Advantageous mutations occur often, and many fixation events are due to positive selection.

Front 47

A species of rodent has a population size of 100,000 individuals, and the per gene mutation rate is 10–6. The average heterozygosity of this species is 0.0909. Another species of rodent in the same genera has twice as many individuals (200,000). Assuming that mutation rates are the same for both species, what would you expect the average heterozygosity of the second species to be?
a. 0.1818
b. 0.1667
c. 0.0909
d. 0.0454
e. 0.9191

Back 47

b. 0.1667

Front 48

mtDNA lineages coalesced over a hundred thousand years ago (156 to 250 Kya) in a putative individual who has been dubbed “mitochondrial Eve.” What does this name actually mean?
a. The human population at the time had only one female.
b. The name “Eve” first appeared in the historical record over a hundred thousand years ago.
c. Genetic drift does not affect coalescent times.
d. There are many origins for modern Homo sapiens.
e. Other females lived at the time, but their mtDNA is absent from today’s population.

Back 48

e. Other females lived at the time, but their mtDNA is absent from today’s population.

Front 49

Which of the following statements about genetic drift is true?
a. Mildly disadvantageous alleles can sometimes increase in frequency due to genetic drift.
b. Evolution by random genetic drift proceeds faster in large populations.
c. Linkage disequilibrium cannot occur because of genetic drift.
d. New mutations that are neutral are less likely to be fixed in small populations.
e. Heterozygosity is unaffected by genetic drift.

Back 49

a. Mildly disadvantageous alleles can sometimes increase in frequency due to genetic drift.

Front 50

A small population of three-spined stickleback fish lives in an Alaskan lake. Two alleles segregate at a neutral locus (A and B). The allele frequency of the A allele is 0.78. Which of the following allele frequencies would most likely be found in the next generation?
a. 0.5
b. 0.51
c. 0.79
d. 0.9
e. 0.1

Back 50

c. 0.79