org. evolution - CH 20

Why can symptoms like fever or pain be beneficial rather than harmful?

Some disease symptoms are defenses, meaning they are evolved responses that help the body fight infection rather than signs of failure.

How can interactions with other organisms lead to disease?

Disease can result from conflicts with other organisms, where pathogens evolve to exploit hosts, causing harm as a byproduct of their survival and reproduction.

Why can traits that were once beneficial become harmful in modern humans?

Diseases can arise from novel environments (mismatch), where traits adapted to past environments no longer function well under current conditions.

Why might a harmful genetic condition persist in a population?

Some diseases are trade-offs, where a trait provides a fitness advantage in one context but causes harm in another.

Why can evolution produce imperfect or “poor” biological designs?

Diseases can result from constraints, where evolution is limited by historical pathways and cannot produce optimal solutions.

How does sickle-cell anemia illustrate an evolutionary trade-off?

The allele causes disease in homozygotes but provides a survival advantage against malaria in heterozygotes, so it is maintained by natural selection.

Why does natural selection not eliminate the sickle-cell allele?

Because the fitness benefit in malaria environments outweighs the cost, allowing the allele to persist despite its harmful effects.

What determines whether a trade-off trait is maintained in a population?

The balance between its beneficial and harmful effects on reproductive success (fitness) in a given environment.

Why is extremely high virulence not always favored by natural selection?

If a pathogen kills or incapacitates the host too quickly, it reduces opportunities for transmission to new hosts.

Why is extremely low virulence also not favored?

If the pathogen does not replicate enough, it may not reach levels necessary for transmission.

What level of virulence is typically favored by natural selection?

An intermediate level that balances replication and transmission without eliminating the host too quickly.

How do vectors (like mosquitoes) change the evolution of virulence?

When transmission does not depend on host mobility, pathogens can evolve higher virulence because the host’s condition no longer limits spread.

How can waterborne transmission influence virulence?

Because transmission does not require host mobility, it can favor higher virulence, similar to vector-based transmission.

How can human behavior influence the evolution of pathogen virulence?

Practices like sanitation, clean water, and hygiene reduce transmission, which can select for less virulent strains.

What is pleiotropy in the context of evolution?

A single gene affects multiple traits or life stages.

What is antagonistic pleiotropy?

A gene has beneficial effects early in life but harmful effects later in life.

Why can genes with harmful late-life effects persist in a population?

Because natural selection is stronger on traits that affect early-life reproduction, so early benefits outweigh later costs.

What is the key idea behind Williams’ explanation for aging?

Aging evolves because alleles that improve early-life fitness are favored, even if they cause decline later in life.

Why does natural selection weaken with age?

Because fewer individuals survive to older ages, so late-life traits have less impact on reproductive success.

Is a fever caused by the pathogen or the body in response to the pathogen?
A. Pathogen
B. Body

B

In some populations the frequency of the allele for sickle-cell anemia is as high as 0.17. Why would the allele for a fatal disease be so abundant?
A. Evolution hasn’t had time to eliminate it yet
B. Sickle cell anemia causes people to reproduce more
C. The allele results in other benefits

C

What best explains why Chile’s strain of cholera became more benign than other regions of South America?
A. Chile has better access to antibiotics
B. Chileans have alleles to fight infectious bacteria diseases
C. Chile has better water treatment practices
D. Chile has fewer people

C

Which nucleotide region is most likely to exhibit change via genetic drift?
A. Intron region
B. Coding region
C. Regulatory region
D. Non-coding RNA region

A

Two pregnant female parrots fly to a new island. Each female lays a clutch of 5 eggs per year. Linda has a genotype that results in a 1-year lifespan, and Barbara has a 2-year lifespan genotype. Assuming all else is equal, which female should produce the most offspring?
A. Linda
B. Barbara
C. They should produce about the same number of offspring

B

Is early senescence evolutionarily stable?
A. Yes
B. No
C. Not sure

B

Why should the effects of an allele matter more when expressed in youth than those that occur in older ages?
A. Children have less well-developed immune systems
B. Elderly individuals are past their reproductive phase
C. Children cannot yet fend for themselves
D. Elderly individuals have more support from their communities

B

Imagine a population of opossum introduced to a small island with few predators. According to the antagonistic pleiotropy theory, how should the timing of senescence change?
A. Senescence should begin sooner
B. Senescence should begin later
C. The timing of senescence should not change

B

Two pregnant female mice are brought to a new island. Each female produces a litter of 5 pups once a year. Brittany has a 1-year lifespan allele, and Christina has a 2-year lifespan allele. However, few mice live to 2 years due to predation. Assuming all else is equal, which female should produce more offspring?
A. Brittany
B. Christina
C. They should produce about the same number of offspring

A

Large animals tend to age more slowly than small animals. Can the antagonistic pleiotropy theory explain this pattern?
A. Yes
B. No

A

Can the lack of aging in birds compared to mammals be explained by antagonistic pleiotropy?
A. Yes
B. No

A