QUIZ : Lecture I

Question 1

Which of the following BEST defines evolution?
A) The process by which individuals become more complex over time
B) The accumulation of mutations that always increase fitness
C) The change in allele frequencies or heritable gene expression across generations
D) The ability of individuals to change their traits within a lifetime

Answer 1

C) The change in allele frequencies or heritable gene expression across generations

Question 2

A population of interbreeding organisms undergoes a shift in allele frequencies over multiple generations. Which mechanism could NOT be responsible for this change?
A) Genetic drift
B) Natural selection
C) Epigenetic inheritance
D) Somatic mutations in non-reproductive cells

Answer 2

D) Somatic mutations in non-reproductive cells

Question 3

Which of the following evolutionary mechanisms is entirely random?
A) Natural selection
B) Mutation
C) Genetic drift
D) Epigenetic inheritance

Answer 3

C) Genetic drift

Question 4

Why is mutation essential for evolution?
A) It generates new genetic variation that other mechanisms act upon
B) It always leads to beneficial adaptations
C) It increases the complexity of organisms over time
D) It ensures the survival of a population

Answer 4

A) It generates new genetic variation that other mechanisms act upon

Question 5

A scientist observes that environmental stress leads to heritable changes in gene expression without altering DNA sequences. Which mechanism is most likely responsible?
A) Genetic drift
B) Epigenetic inheritance
C) Migration
D) Natural selection

Answer 5

B) Epigenetic inheritance

Question 6

A population of lizards is separated by a river, preventing gene flow. Over time, the two groups develop distinct allele frequencies. This is an example of:
A) Migration
B) Genetic drift
C) Epigenetic inheritance
D) Natural selection

Answer 6

B) Genetic drift

Question 7

Why can’t natural selection occur without genetic or epigenetic variation?
A) There would be no differences for selection to act upon
B) Populations would always become more fit over time
C) Mutation rates would increase instead
D) Allele frequencies would remain static forever

Answer 7

A) There would be no differences for selection to act upon

Question 8

Which of the following best describes natural selection?
A) A random process that changes allele frequencies
B) A process that only removes individuals from a population
C) A non-random process that increases the frequency of advantageous alleles
D) A mechanism that eliminates all genetic variation over time

Answer 8

C) A non-random process that increases the frequency of advantageous alleles

Question 9

A small group of birds migrates to an island and starts a new population with a different allele composition than the mainland population. This is an example of:
A) Founder effect
B) Bottleneck effect
C) Epigenetic inheritance
D) Natural selection

Answer 9

A) Founder effect

Question 10

A severe drought reduces a fish population to only a few individuals, drastically changing allele frequencies. This is an example of:
A) Founder effect
B) Mutation
C) Bottleneck effect
D) Epigenetic inheritance

Answer 10

C) Bottleneck effect

Question 11

How does migration influence evolution?
A) It introduces new alleles into a population
B) It always decreases genetic variation
C) It prevents natural selection from occurring
D) It only affects small populations

Answer 11

A) It introduces new alleles into a population

Question 12

Which of the following is NOT a major mechanism of evolution?
A) Mutation
B) Genetic drift
C) Epigenetic inheritance
D) Acclimatization

Answer 12

D) Acclimatization

Question 13

Why does HIV evolve resistance to antiviral drugs like AZT so quickly?
A) HIV can directly modify its own genome to counteract the drug
B) HIV has an exceptionally high mutation rate, leading to rapid evolution
C) The human immune system actively repairs mutations in HIV
D) HIV does not mutate, but instead acquires resistance through horizontal gene transfer

Answer 13

B) HIV has an exceptionally high mutation rate, leading to rapid evolution

Question 14

Which of the following best describes how AZT works against HIV?
A) It blocks viral entry into the host cell
B) It prevents the formation of new viral proteins
C) It mimics thymidine and disrupts reverse transcription
D) It attacks the HIV capsid, preventing replication

Answer 14

C) It mimics thymidine and disrupts reverse transcription

Question 15

How does natural selection act on HIV in the presence of AZT?
A) The drug kills all HIV particles equally, making selection irrelevant
B) Mutant HIV strains that can still replicate in the presence of AZT survive and proliferate
C) The immune system eliminates all HIV strains regardless of AZT resistance
D) AZT increases the mutation rate of HIV, creating more resistant strains

Answer 15

B) Mutant HIV strains that can still replicate in the presence of AZT survive and proliferate

Question 16

Why is it difficult to develop a universal vaccine for HIV?
A) HIV evolves too slowly for vaccines to be effective
B) HIV mutates faster than human immune responses and drug development can keep up
C) The human immune system completely clears HIV infections before vaccines can act
D) HIV does not generate an immune response in infected individuals

Answer 16

B) HIV mutates faster than human immune responses and drug development can keep up

Question 17

What is the primary trade-off in HIV’s evolution when it develops AZT resistance?
A) The resistant strain becomes immune to all antiviral drugs but reproduces more slowly
B) The resistant strain’s reverse transcriptase enzyme becomes slower but more accurate
C) The resistant strain is stronger, but it loses the ability to infect T-cells
D) The resistant strain becomes weaker against other medications

Answer 17

B) The resistant strain’s reverse transcriptase enzyme becomes slower but more accurate

Question 18

How does the transmission rate influence HIV’s evolution?
A) Low transmission rates favor high virulence, while high transmission rates favor lower virulence
B) High transmission rates favor highly virulent strains, while low transmission rates favor less virulent strains
C) HIV transmission rate has no effect on virulence evolution
D) High transmission rates eliminate HIV’s ability to mutate

Answer 18

B) High transmission rates favor highly virulent strains, while low transmission rates favor less virulent strains

Question 19

Why does stopping AZT therapy sometimes result in a decrease in drug-resistant HIV strains?
A) The wild-type (non-resistant) HIV strain replicates faster in the absence of AZT
B) The immune system eliminates all drug-resistant strains
C) HIV permanently loses its ability to mutate after AZT removal
D) Drug-resistant strains die immediately after drug withdrawal

Answer 19

A) The wild-type (non-resistant) HIV strain replicates faster in the absence of AZT

Question 20

Why is HIV considered one of the fastest-evolving organisms on Earth?
A) It uses a DNA-based replication system with proofreading mechanisms
B) Its reverse transcriptase enzyme is highly error-prone, leading to frequent mutations
C) It evolves only in response to AZT and other drugs
D) It has a large genome that prevents genetic errors from accumulating

Answer 20

B) Its reverse transcriptase enzyme is highly error-prone, leading to frequent mutations

Question 21

What happens to the HIV population in the presence of AZT?
A) All HIV strains are equally affected, leading to a decrease in overall viral load
B) Mutants with a slow and careful reverse transcriptase enzyme are selected for, increasing AZT resistance
C) AZT completely eliminates HIV by preventing reverse transcription in all strains
D) HIV mutates to directly incorporate AZT into its replication process

Answer 21

B) Mutants with a slow and careful reverse transcriptase enzyme are selected for, increasing AZT resistance

Question 22

Why does high transmission rate favor high virulence in HIV?
A) Highly virulent strains kill the host quickly and always lead to extinction
B) High transmission rates allow fast-growing, highly virulent strains to spread before the host dies
C) Virulence and transmission rate are unrelated in virus evolution
D) Low virulence is always beneficial for viruses, even in high transmission environments

Answer 22

B) High transmission rates allow fast-growing, highly virulent strains to spread before the host dies

Question 23

Why does low transmission rate select for lower virulence in HIV?
A) More virulent strains would kill the host before spreading, leading to their elimination
B) The host’s immune system eliminates only highly virulent strains
C) The virus stops mutating in low transmission environments
D) The host actively selects for less virulent strains through behavioral changes

Answer 23

A) More virulent strains would kill the host before spreading, leading to their elimination

Question 24

How can lowering HIV transmission rates help combat the virus?
A) It reduces the likelihood of more fatal strains evolving
B) It prevents all mutations in the HIV genome
C) It forces the virus to evolve into a completely non-virulent form
D) It eliminates HIV completely by reducing its ability to replicate

Answer 24

A) It reduces the likelihood of more fatal strains evolving

Question 25

Which evolutionary tradeoff influences HIV’s response to AZT treatment? A) The virus must balance slow and careful replication with maintaining high mutation rates B) The virus must choose between integrating AZT into its genome or avoiding it C) The virus evolves to eliminate its dependence on host cells D) The virus must balance high transmission rates with reduced mutation rates

Answer 25

A) The virus must balance slow and careful replication with maintaining high mutation rates

Question 26

How does natural selection act on HIV’s transmission rate? A) When transmission is high, highly virulent strains dominate; when transmission is low, less virulent strains dominate B) Natural selection does not affect transmission rate, as it is controlled solely by human behavior C) HIV actively reduces its own virulence over time in all cases D) The transmission rate has no evolutionary consequences for HIV

Answer 26

A) When transmission is high, highly virulent strains dominate; when transmission is low, less virulent strains dominate

Question 27

Why is HIV considered an evolutionary “arms race” between the virus and the host? A) HIV and human hosts constantly co-evolve, with some humans developing resistance and the virus evolving new adaptations B) HIV mutates to become weaker over time, while the host’s immune system weakens as well C) Humans cannot evolve any resistance to HIV, making it a one-sided battle D) The virus and host do not influence each other’s evolution in any significant way

Answer 27

A) HIV and human hosts constantly co-evolve, with some humans developing resistance and the virus evolving new adaptations

Question 28

How does the evolution of HIV impact the long-term effectiveness of drugs like AZT? A) Drug-resistant strains evolve, making AZT less effective over time B) AZT completely eliminates HIV within a few generations, preventing further evolution C) HIV eventually stops mutating in response to AZT D) AZT forces HIV to become more virulent and lethal in all cases

Answer 28

A) Drug-resistant strains evolve, making AZT less effective over time

Question 29

What would happen if a highly virulent strain of HIV emerged in a population with low transmission rates? A) The strain would die out because it kills the host before spreading B) The strain would immediately become the dominant form of HIV C) The strain would evolve to become even more virulent D) The strain would spread more rapidly in low-transmission populations

Answer 29

A) The strain would die out because it kills the host before spreading

Question 30

Why do some humans have resistance to HIV? A) Genetic mutations in certain populations have provided resistance to specific HIV strains B) Humans have universally evolved complete immunity to HIV over time C) HIV is unable to infect humans with strong immune systems D) HIV can only infect individuals who have been exposed to AZT

Answer 30

A) Genetic mutations in certain populations have provided resistance to specific HIV strains

Question 31

What is the main challenge in using gene therapy to fight HIV? A) HIV mutates rapidly, making it difficult to design a permanent genetic defense B) Gene therapy is ineffective against all viral infections C) Gene therapy eliminates HIV too quickly, causing it to mutate uncontrollably D) Gene therapy encourages HIV to evolve into a non-viral form

Answer 31

A) HIV mutates rapidly, making it difficult to design a permanent genetic defense

Question 32

Why do mutations in the HIV reverse transcriptase gene make the virus resistant to AZT? A) The mutations allow reverse transcriptase to recognize AZT and use it more efficiently B) The mutations prevent AZT from stopping reverse transcription, allowing the virus to replicate C) AZT forces the virus to stop using RNA, switching to a DNA genome instead D) The mutations enable HIV to completely eliminate AZT from the host’s system

Answer 32

B) The mutations prevent AZT from stopping reverse transcription, allowing the virus to replicate

Question 33

What happens to the HIV population when AZT therapy is discontinued? A) Drug-resistant mutants are permanently fixed in the population B) Back mutations that restore the original, faster reverse transcriptase enzyme are favored C) HIV loses its ability to replicate and becomes non-viable D) The HIV population remains unchanged because selection no longer acts on the virus

Answer 33

B) Back mutations that restore the original, faster reverse transcriptase enzyme are favored

Question 34

Why do back mutations that restore the original reverse transcriptase sequence get selected for when AZT therapy stops? A) The original form of reverse transcriptase replicates faster, allowing those mutants to outcompete the slower AZT-resistant strains B) The immune system eliminates AZT-resistant strains once the drug is removed C) The virus stops mutating once AZT is no longer present D) HIV cannot survive without reverting to its original form

Answer 34

A) The original form of reverse transcriptase replicates faster, allowing those mutants to outcompete the slower AZT-resistant strains

Question 35

What does the evolution of HIV in response to AZT therapy demonstrate? A) Natural selection acts on mutations that improve reproductive success B) Drug resistance in viruses is random and not influenced by selection C) HIV evolves to become weaker over time in all cases D) Viruses cannot adapt to changes in drug treatment

Answer 35

A) Natural selection acts on mutations that improve reproductive success

Question 36

If AZT therapy is stopped, why do fast and sloppy replicating strains of HIV eventually dominate? A) They outcompete slower strains by producing more viral copies in a shorter time B) They evolve complete immunity to all antiviral drugs C) They suppress the host’s immune system more effectively D) They become less virulent and more likely to establish long-term infections

Answer 36

A) They outcompete slower strains by producing more viral copies in a shorter time

Question 37

What is the consequence of stopping and restarting AZT therapy multiple times? A) It allows the HIV population to cycle between resistant and non-resistant strains B) It permanently fixes AZT-resistant strains in the population C) It eliminates HIV completely by confusing the virus D) It prevents the evolution of AZT resistance altogether

Answer 37

A) It allows the HIV population to cycle between resistant and non-resistant strains

Question 38

Which of the following best describes the relationship between AZT therapy and the evolution of HIV? A) Evolution is a dynamic process that changes based on the presence or absence of selective pressures like AZT B) Once HIV evolves resistance to AZT, it remains permanently drug-resistant C) HIV does not evolve in response to drug treatment because mutations are random D) AZT-resistant strains of HIV are always slower and never revert to faster replication rates

Answer 38

A) Evolution is a dynamic process that changes based on the presence or absence of selective pressures like AZT