D4.1 Natural selection

By the end of the 19^th century in England, the dark form of the moth Biston betularia formed up to 98% of the total population in industrial areas. From 1970, the percentage of dark forms decreased significantly. What is an explanation for the decrease?

A. An increase in environmental pollution killed the dark forms more than the light forms.

B. Reduction of pollution resulted in greater camouflage for light forms of the moth.

C. Dark forms could no longer find mates.

D. Light forms had superior feeding mechanisms.

Answer: B

A. Incorrect. Pollution had already caused dark forms to dominate in the 19^th century; the question states the decrease happened after 1970 when pollution decreased.

B. Correct. As air quality improved, trees became cleaner and lighter in color. This favored the survival of light-colored moths due to natural selection. They had better camouflage from predators.

C. Incorrect. There is no evidence that mating behavior changed; the main factor was predation and camouflage.

D. Incorrect. The change in population was due to predation and camouflage, not feeding ability.

Which is an example of natural selection?

A. A giraffe stretching its neck to reach higher leaves

B. A juvenile bird learning to sing

C. Development of antibiotic resistance in bacteria

D. Selective breeding of tail-less cats

Answer: C

A. Incorrect. This is an example of individual behavior, not a heritable change in population over generations.

B. Incorrect. Learning is acquired, not inherited, so it is not natural selection.

C. Correct. Bacteria with genetic mutations that confer resistance survive and reproduce, showing natural selection in action.

D. Incorrect. This is artificial selection, controlled by humans, not natural selection.

What is required for natural selection to occur?

I. Acquired characteristics

II. Advantageous characteristics

III. Genetic variation

A. I only

B. I and III only

C. II and III only

D. I, II and III

Answer: C

A. Incorrect. Characteristics acquired (I) during an organism lifetime like muscle growth from exercise cannot be inherited, so they do not contribute to natural selection. 

B. Incorrect. Characteristics acquired (I) during an organism lifetime like muscle growth from exercise cannot be inherited, so they do not contribute to natural selection. Genetic variation (III) within a population is required for natural selection to act upon. Without variation, all individuals are equally affected by selection pressures.

C. Correct. Traits that increase organism survival or reproductive success are favored and more likely to be passed on (II). Genetic variation (III) within a population is required for natural selection to act upon. Without variation, all individuals are equally affected by selection pressures.

D. Incorrect. Characteristics acquired (I) during an organism lifetime like muscle growth from exercise cannot be inherited, so they do not contribute to natural selection. Traits that increase organism survival or reproductive success are favored and more likely to be passed on (II).  Genetic variation (III) within a population is required for natural selection to act upon. Without variation, all individuals are equally affected by selection pressures.

Which process results in decreased variation?

A. Meiosis

B. Mutation

C. Sexual reproduction

D. Natural selection

Answer: D

A. Incorrect. Meiosis increases variation through independent assortment and crossing over.

B. Incorrect. Mutations introduce new genetic variation.

C. Incorrect. Sexual reproduction shuffles alleles, increasing variation among offspring.

D. Correct. Natural selection favors certain traits and removes less advantageous alleles from the population, reducing variation over time.

Some strains of the pathogenic bacterium Staphylococcus aureus have developed mechanisms that protect them against foreign DNA. What effect does this have on the evolution of antibiotic resistance in these strains of S. aureus?

A. Slower evolution, as bacteria with the antibiotic resistance gene will not reproduce

B. Slower evolution, as the antibiotic resistance gene from other species will not be accepted

C. Faster evolution, as mutations within a population are less likely to occur

D. Faster evolution, as antibiotic resistance genes can only be passed to individuals of the same species

Answer: B

A. Incorrect. Antibiotic resistance does not cause the bacteria not to reproduce.

B. Correct. If the bacteria block foreign DNA, they cannot acquire new resistance genes via horizontal gene transfer, slowing the spread of antibiotic resistance.

C. Incorrect. Preventing foreign DNA does not increase mutation rates.

D. Incorrect. Limiting gene transfer to the same species does not speed up evolution. It restricts the acquisition of new traits from other species.

Natural selection can operate in different ways. What is the effect of disruptive selection?

A. It eliminates individuals with intermediate forms of a characteristic.

B. It eliminates individuals at random regardless of their characteristics.

C. It favors individuals with intermediate forms of a characteristic.

D. It favors individuals at one extreme of the range of variation in a characteristic.

Answer: A

A. Correct. Disruptive selection favors individuals at both extremes of a trait and selects against intermediates.

B. Incorrect. Natural selection is not random. It depends on the trait and its effect on fitness.

C. Incorrect. This describes stabilizing selection, not disruptive selection.

D. Incorrect. This describes directional selection, not disruptive selection.

The table shows the estimated total number of genes in several organisms.

What can be deduced from the information in this table?

A. Throughout evolution, the number of genes increases.

B. The domestic dog is more closely genetically related to the fruit fly than to the human.

C. The number of genes does not determine evolutionary success.

D. Humans produce about half as many proteins as rice.

Answer: C

A. Incorrect. The table shows no consistent increase. Some simpler organisms (rice) can have more genes than more complex ones (human).

B. Incorrect. Gene counts alone does not indicate genetic relatedness.

C. Correct. Complexity or evolutionary success is not strictly correlated with total gene number.

D. Incorrect. Gene numbers are not equivalent to protein numbers. Alternative splicing means humans can produce many more proteins than the number of genes suggests.

Explain the consequence of overpopulation on the survival and reproduction of better adapted individuals within a population. [3]

Three of the following: 

a. better adapted tend to survive more 

b. better adapted reproduce/produce more offspring 

c. pass on characteristics to their offspring when they reproduce

d. their frequency increases within the population due to natural selection 

e. leading to evolution 

Sample answer:

When overpopulation occurs, individuals that are better adapted tend to survive more successfully [1]. These better-adapted individuals reproduce and produce more offspring [1]. They pass on their advantageous characteristics to their offspring [1]. As a result, the frequency of these traits increases within the population due to natural selection [1]. Over time, this process can lead to evolution of the population [1].

Explain how natural selection can cause mate selection behavior patterns to develop in a species such as eastern bluebirds. [3]

Three of the following:

a. natural selection favours specific types of mate selection/behaviour

b. behaviour/mate selection increases the chances of survival/reproduction

c. chosen organisms/males will leave more offspring

d. pass on genes for behavior to offspring

e. behaviour/allele will become more prevalent/frequent in a population

Sample answer:

Natural selection can favor specific types of mate selection or behavior in eastern bluebirds [1]. These behaviors increase the chances of survival and reproduction of individuals displaying them [1]. The chosen organisms, usually males, leave more offspring [1]. The genes for these behaviors are passed on to the offspring [1]. Over generations, the behaviors or alleles become more prevalent or frequent in the population [1].

Explain how natural selection can cause traits such as drought resistance to develop in wild plants. [7]

Seven of the following: 

a. natural selection occurs if there is variation in degree of drought resistance among members of a population/same species

b. variation is caused by mutations when changes occur in the DNA/nucleic bases/chromosomes

c. variation during meiosis occurs with separation of chromosomes

d. variation occurs during sexual reproduction as different alleles combine

e. some variations make some plants more drought-resistant

f. example of variations: deeper roots/more storage tissue for water/thicker cuticles/less opening of stomata/other verifiable variations

g. these variations let some survive and reproduce better/have more offspring OR these variations confer selective advantage

h. these variations/characteristics are passed onto offspring which survive better

i. natural selection increases the frequency of these characteristics

j. eventually leads to changes/evolution in the species / more drought-resistant plants

Sample answer: 

Natural selection can cause traits such as drought resistance to develop in wild plants because there is variation in the degree of drought resistance among members of a population or the same species [1]. This variation is caused by mutations in DNA, nucleotides, or chromosomes [1]. Variation also arises during meiosis, through the separation of chromosomes, and during sexual reproduction as different alleles combine [1]. Some of these variations make certain plants more drought resistant [1]. Examples of such variations include deeper roots, more storage tissue for water, thicker cuticles, or less opening of stomata [1]. These advantageous variations allow some plants to survive and reproduce better, producing more offspring [1]. Over generations, natural selection increases the frequency of these drought-resistant characteristics, eventually leading to evolutionary changes in the species [1].