Question 1

Imagine two populations of snails that are polymorphic for sexual reproduction.In each of the two populations,several asexual lineages and a panmictic,sexually reproducing subpopulation of snails are living in the same environment.Several years ago,a new pathogen was detected in the first population.This pathogen is transmitted predominantly between parents and their offspring,but on occasion,it is also transmitted horizontally between unrelated individuals.The pathogen is now infecting both sexual and asexual individuals.Since the introduction of the pathogen,the formerly stable ratio of sexual to asexual snails has shifted significantly in favor of the sexually reproducing individuals.At the same time,the second population became infected with a pathogen that is almost always transmitted horizontally.In the second population,no shift in the ratio of sexuals to asexuals has been observed.Speculate on why the difference in transmission between the two pathogens may have shifted the proportion of sexual reproduction in the first but not in the second population.Limit your answer to one or two sentences.

Accepted Answer

Vertically transmitted pathogens are expected to adapt to their genetically identical lineage of asexual hosts.Sexual reproduction makes such adaptation more difficult.

Question 2

What two main factors are responsible for the asymmetry in the coevolutionary arms race between microbial pathogens and their multicellular hosts?

Accepted Answer

When compared to their multicellular hosts,microbial pathogens have much shorter generation times and much higher population numbers.

Question 3

Why is there no lifelong vaccine protection against flu as there is by a measles vaccine?

Accepted Answer

A)  The variety of flu strains is too great to be captured by a single vaccine.
B)  Flu can escape host immunity by evolving new variants that re-infect hosts.
C)  The flu is too virulent to effectively vaccinate against.
D)  The antigenic memory against flu has a short half-life. B

Question 4

Ask a question about fever at each of Tinbergen's four levels (1,2,3,and 4)of explanation.Limit your answer to one sentence for each level.

Accepted Answer

The answer of Ask a question about fever at each...

Question 5

Figures A and B show the effect of an early- and a late-acting mutation on the lifetime fitness of individuals.Based on the graphs,how would you determine which of the two mutations had a greater effect on lifetime fitness? Limit your answer to one sentence.

Accepted Answer

The answer of Figures A and B show the effect...

Question 6

What is the likely phylogenetic explanation for the crossing of food and air pathways in humans?

Accepted Answer

A)  A connection between the two previously separated pathways evolved to allow for an alternative air intake in case of a "stuffy nose."
B)  Lungs evolved from pouches in the digestive system.
C)  Access to odor receptors in the nose allowed for assessing food quality before swallowing.
D)  A connection between both pathways allowed for a more efficient swallowing mechanism.

Question 7

Patients with severe bacterial sepsis who develop a fever have higher survival rates than those who do not develop a fever.Does this observation provide causative evidence for the beneficial role of fever in fighting infections?

Accepted Answer

A)  Yes, patients who develop a fever will have a higher mean fitness.
B)  Yes, developing a fever is correlated with a strong immune system.
C)  No, the disease in nonfever patients may have been too severe to allow the body to develop a fever.
D)  No, fever has been shown by other studies to be inconsequential in fighting infections.

Question 8

Which of the two viral phylogenies below shows the signature of a recent,rapid population expansion? Justify your answer in one or two sentences.

Accepted Answer

The answer of Which of the two viral phylogenies below...

Question 9

The figure below shows the effect of an antagonistic pleiotropic mutation (A).What would be the effect of a mutation (B)that delayed the onset of reproduction without changing the survival curve?

Accepted Answer

A)  Genotypes carrying A and B would have a higher fitness than genotypes carrying A without B.
B)  Genotypes carrying A and B would have a lower fitness than genotypes carrying A without B.
C)  B would not have any effect on the fitness of individuals with A.
D)  We cannot determine the effect of B without the survival curve for individuals that are wild-type at the locus affected by A.

Question 10

.Ackermann and colleagues (2003)investigated senescence in bacteria.What do the following results demonstrate and why are they surprising given evolutionary theory on aging?

Accepted Answer

A)  Bacteria do not senesce. Every organism should show trade-offs between fitness and longevity.
B)  Bacteria do not senesce. Extrinsic mortality is not constant throughout the life of a bacterial cell.
C)  Bacteria do senesce. Pleiotropy is the rare exception in simple bacterial genomes.
D)  Bacteria do senesce. Cell propagation and reproduction are the same in bacteria.

Question 11

Which part of the immune system's "learning system" is responsible for maintaining life-long immunity against measles after a measles infection?

Accepted Answer

A)  Somatic recombination
B)  Affinity maturation
C)  Clonal expansion
D)  Retention of responding cells

Question 12

Which of the following are strategies with which vertebrate hosts counteract the asymmetries between most pathogens and their hosts?

Accepted Answer

A)  Somatic mutation and lateral gene transfer between immune system cells
B)  Somatic recombination and restriction endonucleases
C)  Somatic mutation and recombination
D)  Rapid population growth of host organisms and clonal expansion

Question 13

Name three methods that pathogens use to subvert their host's immune system.

Accepted Answer

The answer of Name three methods that pathogens use to...

Question 14

Under which of the following evolutionary explanations for disease does the antagonistic pleiotropy hypothesis for aging fall?

Accepted Answer

A)  Natural selection has not had time to catch up with environmental changes.
B)  Natural selection lacks foresight; we are stuck with historically contingent relics of the past.
C)  Natural selection favors reproductive success, even at the expense of vulnerability to disease.
D)  Some disease symptoms, though unpleasant, are actually beneficial.

Question 15

Which of the following hypothetical viruses would likely show a "cactus-shaped" population phylogeny?

Accepted Answer

A)  A mutualistic virus that is vertically transmitted
B)  A highly virulent virus, like Ebola, that kills its host before the build-up of any immunity
C)  A highly virulent virus that results in life-long immunity and that can only infect naïve individuals (e.g., young children)  that have never encountered any of the virus's strains
D)  A virus that can reinfect previously infected hosts via escape mutants

Question 16

Can you think of examples,similar to the crossing pathways of food and air,in human anatomy or physiology that represent an "imperfect design" due to evolutionary history?

Accepted Answer

The answer of Can you think of examples,similar to the...

Question 17

Under which hypothesis may pathogens ultimately be responsible for the evolution of sexual reproduction in multicellular organisms?

Accepted Answer

A)  Good genes hypothesis
B)  Red Queen hypothesis
C)  Mutation accumulation hypothesis
D)  Rate-of-living hypothesis

Question 18

Individuals of a certain tree species experience a markedly higher mortality rate at age 200 and beyond.Name two other changes you would expect in 200-year-old trees if this increase in mortality was accompanied by senescence.

Accepted Answer

The answer of Individuals of a certain tree species experience...

Question 19

Which of the following represents a similarity between the evolution of tumors and the vertebrate immune response?

Accepted Answer

A)  Both involve somatic mutations.
B)  Both involve sexual reproduction.
C)  Both can be examined using the Hardy-Weinberg principle.
D)  Genetic drift is negligible in both systems.

Question 20

Many wild mushrooms make delicious food,but some are highly toxic and can result in a fatal meal.Apply the principle of asymmetric harm to mushroom identification,and recommend a strategy for mushroom identifiers.

Accepted Answer

The answer of Many wild mushrooms make delicious food,but some...

Exam 20: Evolution and Medicine