Deck 8: Evolution in Finite Populations

Question 1

Consider a population with a constant size,Nₑ = 5000,that experiences a mutation rate of 0.00005,with an initial F value of 0.15.What is the probability that two alleles selected at random from the offspring of this population will be identical by descent?

A)0
B)0.15
C)0.30
D)0.40
E)None of the above

Answer 1

B

Question 2

In a diploid population,the threshold at which selection is likely to outweigh drift is when s (the selective advantage in this case)is

A)> 1/2Ne.
B)> Ne.
C)> 2Ne.
D)> 4Ne.
E)> Ne/4.

Answer 2

A

Question 3

The neutral theory of molecular variation posits that most

A)mutations are neutral.
B)substitutions are neutral.
C)mutations are deleterious.
D)B and C
E)All of the above

Answer 3

B

Question 4

The ancestor to the Hawaiian crickets in the genus Laupala originally colonized the oldest of the islands in the Hawaiian archipelago.As new islands were formed,crickets from the older island would colonize the younger island.Because members of this genus are flightless,these migration events were likely to be extremely rare and would include a small number of migrants.Nonselective differences in allele frequencies in this genus are likely due to

A)differences in mutation rate.
B)a founder event.
C)genetic drift subsequent to colonization.
D)A and C
E)B and C

Question 5

One consequence of genetic drift is

A)increasing heterozygosity in the population.
B)the maintenance of multiple alleles across long periods of time.
C)that populations diverge in terms of their allele frequencies.
D)that populations maintain the same set of alleles through time.
E)All of the above

Question 6

Consider a collection of 50 distinct alleles,each at equal frequency in a population.The time before the first coalescent event will be shortest if

A)Ne = 100
C)Ne = 100,000,000
B)Ne = 100,000
D)Ne = 1,000,000,000

Question 7

If two randomly selected gene copies are sampled from a population of oak trees at a locus for which there is no selection,assortative mating,or migration,how many mutations would we expect these alleles to differ by?

A)2k
B)4k
C)2Ne
D)4Ne
E)4Nem

Question 8

The inbreeding effective population size is often lower than the census size of a population because of

A)inbreeding depression.
B)fluctuating population size.
C)uneven sex ratios.
D)B and C
E)All of the above

Question 9

If it takes many generations for a collection of gene copies to coalesce to a single gene copy,we can infer that

A)Ne is small.
B)Ne is large.
C)there are few alleles in the population.
D)Ho will be small.
E)None of the above

Question 10

The figure above illustrates the

A)increase in homozygosity with time.
B)the effect of over-fishing on heterozygosity.
C)the decline of heterozygosity with time.
D)B and C
E)All of the above

Question 11

Refer to the figure above to answer the following question.Which of the following mutations to a codon is most likely to be selectively neutral?

A)UUG ® CUG
B)AUA ® AUG
C)AAC ® AAA
D)UGC ® UGA
E)AGC ® AGA

Question 12

The figure above demonstrates the

A)effects of genetic drift in small populations.
B)relationship between population size and the effects of selection.
C)relationship between population size and the effects of mutation.
D)relationship between population size and effective population size.
E)relationship between population size and the effects of migration.

Question 13

Population bottlenecks occur when

A)a large number of genetically diverse individuals found a new population.
B)population size dramatically increases.
C)a consistently large population experiences a brief period of small size.
D)drift in consistently small populations become fixed for a single allele.
E)inbreeding is high.

Question 14

Consider a population with an effective size of 4000 and 32 segregating alleles.On average,how many generations would it take for all 32 alleles to coalesce to a single,ancestral allele?

A)32
B)128
C)1000
D)16000
E)Coalescence of all 32 alleles will never occur.

Question 15

A rancher genotypes all of her 150 head of cattle.In her herd,25 are A₁A₁,75 are A₁A₂,and 50 are A₂A₂.Assuming there is random mating,no selection,no mutation,and no new cattle are introduced into the population,what is the probability that the A₁ allele will be fixed?

A)0
B)0.0127
C)0.4167
D)0.6588
E)1

Question 16

The variable F is

A)the probability of two alleles being identical by descent.
B)a measurement used to quantify the loss of variation due to drift over time.
C)a measure of the degree of inbreeding.
D)A and B
E)All of the above

Question 17

A researcher examines a microsatellite locus in a wild population of D.melanogaster.He finds that in a sample of 50 individuals,20 different alleles are segregating.The best explanation for the presence of all of these alleles is

A)balancing selection.
B)mutation.
C)the neutral theory.
D)overdominance.
E)the law of large numbers.

Question 18

Population bottlenecks can lead to the fixation or loss of alleles in otherwise large populations because the bottleneck

A)selectively eliminates or fixes alleles.
B)reduces the effective population size to close to the size of the bottleneck.
C)allows migrant alleles to overwhelm native alleles.
D)A and B
E)All of the above

Question 19

Consider a population of size Nₑ with a new mutation that confers a fitness advantage of 1 + s.This new allele will be more likely to go to fixation due to selection if

A)Ne is large.
B)Ne is small.
C)s is small.
D)s is large.
E)A and D

Question 20

A founder event changes allele frequencies because

A)only a subset of genes in the original population are observed in the founder population.
B)of random sampling of alleles from the original population.
C)of the coalescent process.
D)A and B
E)All of the above

Question 21

If neutral mutations occur at the rate of 0.5 per individual per generation,the rate of neutral substitutions per generation in that population will equal

A)2Ne × 0.5.
B)(1/2Ne) × 0.5.
C)2Nekn × 0.5.
D)0.5.
E)None of the above

Question 22

How do the data in the following table support the neutral theory?

Question 23

The nearly neutral theory

A)relaxes assumptions concerning the selective neutrality of alleles.
B)can be used to explain the fact that substitution rate is approximately independent of generation time.
C)suggests that mildly deleterious mutations can become fixed more readily in smaller populations due to drift.
D)A and C
E)All of the above

Question 24

A population of fruit flies is maintained at 4000 individuals for 10 generations.During the 11ᵗʰ generation,the professor in charge of the flies forgot to buy fly food and only 100 flies survived.Estimate the effective population size of this population over the first 11 generations.

Question 25

In which of the demographic patterns in the figure below would you expect the final coalescent event to be most recent? Explain your answer.

Question 26

Consider a population of 10,000 pigeons founded by a population in which no alleles were identical by descent.After 30 generations in this Wright-Fisher population,what will the expected identity by descent be?

Question 27

The figure below presents the genotypes of individuals in several island populations at three points in time (t = 0,t = 4,t = 32).What effect of genetic drift does this figure demonstrate?

Question 28

The substitution rate is expressed in terms of substitutions per generation; however,molecular clock estimates show that substitutions accumulate annually regardless of the generation time.What explanation for this discrepancy is illustrated in the figure below?

Question 29

The molecular clock has limited usefulness for estimating divergence times among species because of

A)the saturation of DNA sequences.
B)the variation in substitution rate between lineages and loci.
C)small population sizes.
D)A and B
E)All of the above

Question 30

What are the observed and expected heterozygosities in a population that has three genotypes with the following occurrences: f(A₁A₁)= 100,f(A₁A₂)= 25,f(A₂A₂)= 100.

Question 31

Explain why the probability of fixation of a new beneficial allele is independent of population size in Haldane's model of selection and drift.

Question 32

It's well known that different lineages experience different mutation rates,even at the same locus.Consider two species,1 and 2,that experience mutations rates of m₁ < m₂,with populations sizes of Nₑ₁ < Nₑ₂.Which species would you expect to have a lower frequency of heterozygotes at a neutral locus? Explain your reasoning.

Question 33

Which of the following graphs depicts the group with the largest populations? Explain your reasoning.

Question 34

How are the neutral theory of molecular evolution and the Hardy-Weinberg equilibrium similar?

Question 35

Imagine that,of three species,it is known that species 1 and 3 were separated 10 million years ago,based on geologic measurements.Genetic analysis at a neutral locus indicates that these species differ by 100 substitutions.If there are 10 substitutions separating species 1 and 2,approximately how long ago did these species diverge?

A)0.1 million years ago
B)1 million years ago
C)10 million years ago
D)100 million years ago
E)Cannot be determined based on the information provided

Question 36

Greater prairie chickens,large birds related to grouse,once maintained population sizes of hundreds of thousands on the North American Great Plains.As more and more of the native grassland was converted to farms,the number of greater prairie chickens declined,and the species nearly went extinct due to loss of habitat.Assume that a locus segregating for two alleles,A and a,each with a frequency of 0.5,existed in greater prairie chickens before the reduction of habitat.Further,assume that this species was fragmented into genetically isolated populations,containing very limited numbers of individuals.What effect on allele frequencies would one expect to find in the greater prairie chicken populations after the losses and fragmentation of habitat?

Question 37

Please describe the allele substitution rate in terms of the effective population size (Nₑ),the number of neutral loci in the population (k)and mutation rate (n).Please show all of your work.

Question 38

At how many generations back do all of the alleles in the current population coalesce to a single allele?