AP Biology Quiz: Introduction To Natural Selection

20 questions · exam conditions

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Introduction To Natural SelectionQuestion 1 of 20

In a bird population, beak depth varies and is heritable, influenced by alleles D (deeper beak) and d (shallower beak). A shift in available seeds occurs: most remaining seeds are large and hard, and birds with shallower beaks crack them less efficiently and produce fewer offspring. Birds with deeper beaks more often obtain enough food to reproduce. The population continues to interbreed in the same region, with minimal immigration. Which outcome is most likely after several generations?

Allele d increases because birds with shallow beaks can learn new feeding behaviors and pass them on genetically.

Allele frequencies remain constant because food type changes do not affect reproductive output.

Allele D increases because birds with deeper beaks leave more offspring when hard seeds dominate.

Both alleles disappear because the population will stop reproducing until softer seeds return.

Birds with shallow beaks develop deeper beaks during life and transmit that trait to offspring.

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AP Biology Quiz

AP Biology Quiz: Introduction To Natural Selection

Practice Introduction To Natural Selection in AP Biology with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Introduction To Natural Selection, giving you a quick way to practice the rules, question types, and explanations that matter most for AP Biology.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

Allele d increases because birds with shallow beaks can learn new feeding behaviors and pass them on genetically.
Allele frequencies remain constant because food type changes do not affect reproductive output.
Allele D increases because birds with deeper beaks leave more offspring when hard seeds dominate. (correct answer)
Both alleles disappear because the population will stop reproducing until softer seeds return.
Birds with shallow beaks develop deeper beaks during life and transmit that trait to offspring.

Explanation: This question tests understanding of natural selection, the process where heritable traits that improve survival and reproduction become more common in a population over generations. The shift to hard seeds disadvantages birds with shallower beaks (allele d), who feed less efficiently and produce fewer offspring, while deeper-beaked birds (allele D) succeed and reproduce more. Consequently, the frequency of allele D increases, as deeper-beaked birds pass on the trait to more descendants. This change happens at the population level through differential reproductive success under the new food availability pressure. A tempting distractor is choice E, which wrongly suggests shallow-beaked birds develop deeper beaks and transmit them, reflecting the misconception of inheritance of acquired traits. For natural selection questions, always identify the environmental pressure, the heritable variation it acts on, and how it leads to changes in allele frequencies through differential reproduction.

Question 2

In a bird population, beak depth varies and is heritable. After several years of drought, only hard, large seeds remain abundant. Birds with deeper beaks crack these seeds more efficiently and produce more offspring than birds with shallower beaks. Both beak depths continue to occur among nestlings. Which outcome is most likely over generations?

Shallow-beak alleles will increase because shallow-beaked birds avoid competition for large seeds.
Deeper-beak alleles will increase in frequency because birds with deeper beaks leave more offspring. (correct answer)
Birds will develop deeper beaks from cracking seeds, and offspring will inherit the acquired depth.
Allele frequencies will not change because drought is a temporary environmental condition.
The population will lose beak-depth variation because natural selection prevents genetic variation from arising.

Explanation: This question tests understanding of natural selection, the process where heritable traits that enhance survival and reproduction become more common in a population over generations. Drought leaves only hard, large seeds, which deeper-beaked birds crack more efficiently and use to produce more offspring. As a result, deeper-beaked birds contribute more to subsequent generations, increasing deeper-beak alleles in the population. This adaptation occurs through selection for effective foraging, with both beak depths persisting among nestlings. A tempting distractor is choice C, which incorrectly assumes birds develop deeper beaks from use and pass this on, representing the misconception of inheritance of acquired traits. For natural selection questions, always identify the selective pressure, the heritable trait, and how it affects reproductive success at the population level.

Question 3

A freshwater fish population contains heritable variation in tolerance to low dissolved oxygen, influenced by alleles O (higher tolerance) and o (lower tolerance). During summer, algal blooms repeatedly reduce dissolved oxygen for several weeks, and fish with lower tolerance die at higher rates before spawning. Survivors reproduce within the same lake, and offspring oxygen tolerance resembles parental genotypes. Migration into the lake is rare. Which outcome is most likely after several bloom seasons?

The o allele increases because low oxygen causes fish to switch on genes that create lower tolerance.
The frequency of allele O increases because more O-bearing fish survive to reproduce during low oxygen. (correct answer)
Allele frequencies stay constant because the bloom affects all fish equally regardless of genotype.
All fish become highly tolerant within one generation because exposure changes their DNA permanently.
Both alleles disappear because environmental stress prevents inheritance of oxygen tolerance.

Explanation: This question tests understanding of natural selection, the process where heritable traits that improve survival and reproduction become more common in a population over generations. Repeated algal blooms reduce oxygen, causing higher mortality in fish with low-tolerance allele o before spawning, while high-tolerance fish with allele O survive and reproduce more often. This differential survival leads to an increase in the frequency of allele O, as surviving fish pass on the trait to a larger share of the next generation. At the population level, the heritable variation in oxygen tolerance drives this change under the consistent selective pressure of low oxygen. A tempting distractor is choice D, which incorrectly states that exposure permanently changes DNA in all fish, reflecting the misconception that environments directly alter genes within a generation. For natural selection questions, always identify the environmental pressure, the heritable variation it acts on, and how it leads to changes in allele frequencies through differential reproduction.

Question 4

A population of flowering plants shows heritable variation in flowering time controlled by alleles F (early) and f (late). A new mowing schedule cuts the field in mid-season each year, removing many late-flowering plants before they set seed, while early-flowering plants often produce seeds before mowing. Plants cross-pollinate within the same field, and offspring flowering time resembles parental genotypes. Other environmental factors remain similar across years. Which outcome is most likely over time?

Allele f increases because late flowering allows plants to avoid competition and always increases seed production.
Allele F increases because early-flowering plants contribute more seeds to the next generation under mowing. (correct answer)
Allele frequencies remain unchanged because mowing affects only adult plants, not the next generation.
Late-flowering plants begin flowering earlier after mowing and pass that acquired timing to offspring.
Both alleles become equally frequent because mowing creates a balanced advantage for both flowering times.

Explanation: This question tests understanding of natural selection, the process where heritable traits that improve survival and reproduction become more common in a population over generations. Mowing removes late-flowering plants with allele f before seeding, while early-flowering plants with allele F produce seeds beforehand and contribute more to the next generation. This selective pressure increases the frequency of allele F, as early-flowering individuals pass on the trait more often. At the population level, the heritable variation in flowering time drives evolution under consistent mowing. A tempting distractor is choice D, which claims late-flowering plants change timing and inherit it, illustrating the misconception of Lamarckian evolution. For natural selection questions, always identify the environmental pressure, the heritable variation it acts on, and how it leads to changes in allele frequencies through differential reproduction.

Question 5

In a grass population, plants vary in height due to a heritable gene with alleles H (tall) and h (short). A herd of grazing mammals feeds by clipping vegetation at a consistent height, removing a larger fraction of tall plants before they produce seeds. Short plants are less likely to be clipped and more often set seed. All plants release pollen and seeds within the same field, and no new alleles enter the population. Which outcome is most likely after many generations of grazing?

Allele H increases because tall plants capture more sunlight and always outcompete short plants.
Allele frequencies remain unchanged because grazing affects only plant size, not reproduction.
Allele h increases because short plants contribute more seeds to the next generation than tall plants. (correct answer)
Individual tall plants become short after being clipped and pass that new height to offspring.
Both alleles become equally frequent because grazing creates new mutations at the height gene.

Explanation: This question tests understanding of natural selection, the process where heritable traits that improve survival and reproduction become more common in a population over generations. Grazing mammals clip tall plants with allele H more often before they seed, while short plants with allele h are less affected and produce more seeds, leading to higher reproductive success for short plants. Consequently, the frequency of allele h increases in the population as short plants contribute more offspring that inherit the short height trait. This evolutionary shift happens at the population level due to the selective pressure of grazing favoring the short stature. A tempting distractor is choice D, which erroneously claims that clipped plants change height and pass it on, representing the misconception of Lamarckian evolution. For natural selection questions, always identify the environmental pressure, the heritable variation it acts on, and how it leads to changes in allele frequencies through differential reproduction.

Question 6

A rabbit population varies in fur density due to heritable alleles C (denser coat) and c (less dense coat). Following several unusually cold winters, rabbits with less dense coats experience lower survival before breeding, while rabbits with denser coats more often survive to reproduce. The population remains in the same region with continued interbreeding and little migration. No additional selective pressures are described. Which outcome is most likely after multiple cold winters?

Allele C decreases because dense fur requires more energy and therefore reduces survival in winter.
Allele frequencies remain constant because winter temperatures do not affect reproductive success.
Allele c increases because rabbits with less dense coats can acclimate to cold and pass that to offspring.
The frequency of allele C increases because denser-coated rabbits leave more offspring after surviving winters. (correct answer)
Both alleles disappear because cold winters prevent inheritance of fur density.

Explanation: This question tests understanding of natural selection, the process where heritable traits that improve survival and reproduction become more common in a population over generations. Cold winters reduce survival of rabbits with less dense coats (allele c) before breeding, while denser-coated rabbits (allele C) survive better and reproduce more. This leads to an increase in the frequency of allele C, as denser-coated individuals contribute more offspring inheriting the trait. The population-level shift results from the selective pressure of cold favoring the insulating fur density. A tempting distractor is choice C, which incorrectly states rabbits acclimate to cold and pass it on, representing the misconception of acquired trait inheritance. For natural selection questions, always identify the environmental pressure, the heritable variation it acts on, and how it leads to changes in allele frequencies through differential reproduction.

Question 7

A mouse population has variation in coat color, and the trait is heritable. After snowfall becomes rare, the ground remains dark for most winters. Owls capture light-colored mice more often than dark-colored mice, reducing reproduction of light-colored mice. Which outcome is most likely over generations as dark winters persist?

Light-colored mice will darken their coats in response to winter conditions, preventing allele changes.
Alleles for dark coat color will increase because dark-coated mice contribute more offspring. (correct answer)
Alleles for light coat color will increase because owls remove dark mice that compete for food.
Coat-color alleles will change because the population must match the dark ground to persist.
Allele frequencies will not change because predation changes only appearance, not heredity.

Explanation: This question tests understanding of natural selection through predation on a mouse population. The correct answer is B because natural selection operates when individuals with certain heritable traits (dark coat color) have higher reproductive success due to environmental pressures (owl predation on visible light-colored mice). The stimulus indicates that owls capture light-colored mice more often on dark ground, reducing their reproduction, which means dark-colored mice contribute proportionally more offspring to future generations. Over multiple generations, this differential reproduction causes dark coat color alleles to increase in frequency in the population. Answer A incorrectly suggests that individual mice can change their coat color in response to environmental conditions (acquired characteristics), which would not change allele frequencies since the genetic makeup remains unchanged. When analyzing natural selection, focus on differential reproduction based on heritable traits, not on what individuals might do to survive.

Question 8

In a coastal plant population, leaf waxiness varies due to heritable alleles W (high wax) and w (low wax). During frequent salt-spray events, plants with low wax lose more water and produce fewer seeds. Salt spray intensity remains high for decades. Which explanation best accounts for the expected change in allele frequencies?

Allele w will rise because low-wax plants compensate by producing more seeds after exposure.
Allele W will rise because high-wax plants contribute a larger share of the next generation. (correct answer)
Allele frequencies will stay constant because waxiness is determined only by salt conditions.
Allele W will rise because salt spray directly changes w alleles into W alleles in leaves.
Allele w will be preserved because the population benefits from maintaining low waxiness.

Explanation: This question tests natural selection through differential reproduction based on water retention. The correct answer is B because plants with the W allele (high wax) lose less water during salt spray events and therefore produce more seeds than plants with the w allele. Since seed production directly determines reproductive success, high-wax plants contribute a larger proportion of offspring to the next generation, causing the W allele frequency to increase over time. Answer D incorrectly suggests that environmental conditions can directly change one allele into another, which confuses mutation with selection. Natural selection changes allele frequencies by differential reproduction, not by transforming existing alleles.

Question 9

A frog population has heritable variation in skin peptide composition: allele P produces peptides that inhibit a fungal pathogen, while allele p produces peptides with weaker inhibition. During repeated fungal outbreaks, frogs with weaker inhibition have lower survival to reproduction. If outbreaks continue for many generations, which outcome is most likely?

Allele P will increase because frogs with stronger inhibition leave more offspring after outbreaks. (correct answer)
Allele p will increase because infected frogs develop stronger peptides during their lifetimes.
Allele frequencies will remain stable because pathogens do not influence reproductive success.
Allele P will decrease because selection always favors alleles that were common before outbreaks.
Both alleles will change equally because fungal exposure causes random changes in peptide genes.

Explanation: This question demonstrates natural selection acting on disease resistance. The correct answer is A because frogs with the P allele produce peptides that better inhibit the fungal pathogen, leading to higher survival rates and more offspring compared to frogs with the p allele. During repeated outbreaks over many generations, this reproductive advantage causes the P allele to increase in frequency. Answer B incorrectly suggests that infected frogs can develop stronger peptides during their lifetime and pass this trait on, confusing acquired characteristics with inherited ones. Natural selection acts only on heritable variation that affects reproductive success.

Question 10

A fish population shows heritable variation in body coloration controlled by alleles G (green) and S (silver). In a lake that becomes covered by dense green algae, predatory birds capture silver fish more often than green fish, reducing silver fish reproductive output. If algae cover persists, which outcome is most likely over generations?

Allele S will increase because silver fish learn to hide better in algae during their lives.
Allele frequencies will not change because predation removes individuals randomly from the gene pool.
Allele G will increase because green fish contribute more offspring under sustained bird predation. (correct answer)
Allele G will increase because algae exposure causes fish to switch from S to G alleles.
The population will become greener because fish coloration changes to match algae when needed.

Explanation: This question demonstrates natural selection through camouflage and predation pressure. The correct answer is C because green fish blend with the algae-covered environment, making them less visible to predatory birds and allowing them to survive and reproduce at higher rates than silver fish. Over generations, this differential reproductive success causes the G allele frequency to increase in the population. Answer A incorrectly suggests that individual fish can learn to hide better, confusing behavioral changes within a lifetime with heritable traits. To solve natural selection problems, identify which heritable variant has higher reproductive success in the given environment.

Question 11

In a bird population, beak depth varies due to heritable alleles D (deeper beak) and d (shallower beak). After a drought, mostly large, hard seeds remain; birds with shallow beaks crack fewer seeds and produce fewer fledglings. Drought conditions recur frequently over many generations. Which outcome is most likely?

Allele d will increase because shallow-beaked birds practice cracking hard seeds and improve.
Allele D will increase in frequency because deeper-beaked birds contribute more offspring when hard seeds dominate. (correct answer)
Allele frequencies will not change because seed size affects feeding behavior rather than reproduction.
Allele D will appear in more birds because drought directly alters d alleles into D alleles.
The population will shift to deeper beaks because birds need to crack large seeds to survive.

Explanation: This question tests natural selection through resource utilization efficiency. The correct answer is B because birds with deeper beaks (D allele) can crack large, hard seeds more effectively, allowing them to obtain more food and produce more fledglings than shallow-beaked birds during drought conditions. Over many generations of recurring droughts, this reproductive advantage causes the D allele frequency to increase in the population. Answer E incorrectly uses teleological reasoning by suggesting the population shifts because birds need deeper beaks, rather than recognizing that differential reproduction drives the change. Focus on which variants leave more offspring rather than what the population needs.

Question 12

In a snail population, shell thickness varies and is heritable: allele T produces thicker shells than allele t. A crab predator is introduced and more easily crushes thin-shelled snails, reducing their reproductive output. Crab predation remains high for many generations. Which outcome is most likely in the population?

Allele t will increase because crushed snails stimulate thicker shell growth in surviving snails.
Allele T will increase in frequency because thicker-shelled snails contribute more offspring under predation. (correct answer)
Allele frequencies will not change because predation is unrelated to which snails reproduce.
Allele T will increase because crabs cause t alleles to mutate into T alleles when shells are crushed.
The population will produce thicker shells because snails benefit from resisting crabs.

Explanation: This question tests natural selection through predator-prey interactions. The correct answer is B because snails with thicker shells (T allele) resist crab predation better, allowing them to survive and reproduce at higher rates than thin-shelled snails. Over many generations of high crab predation, this differential reproductive success causes the T allele frequency to increase in the population. Answer D incorrectly suggests that predation can cause one allele to mutate into another, confusing the source of variation with the process of selection. Remember that natural selection sorts among existing heritable variants based on their reproductive success.

Question 13

A grass population includes heritable variation in flowering time: allele E causes earlier flowering than allele e. A mowing schedule removes most plants that have not yet produced seeds by mid-season; earlier-flowering plants set seed before mowing more often. The mowing schedule stays the same for many years. Which outcome is most likely over generations?

Allele e will increase because later-flowering plants grow faster after mowing and catch up reproductively.
Allele frequencies will remain constant because mowing changes plant size but not seed production.
Allele E will increase in frequency because earlier-flowering plants contribute more seeds before mowing. (correct answer)
Allele E will increase because mowing directly converts e alleles into E alleles in surviving plants.
The population will flower earlier because grasses must match the mowing schedule to persist.

Explanation: This question examines natural selection through timing of reproduction. The correct answer is C because plants with the E allele flower earlier and successfully produce seeds before mowing, while later-flowering plants (e allele) are often mowed before setting seed. This difference in reproductive success causes earlier-flowering plants to contribute more offspring to subsequent generations, increasing the E allele frequency over time. Answer A incorrectly suggests that later-flowering plants can compensate after mowing, but the key is that they miss their reproductive opportunity entirely. When analyzing selection scenarios, focus on which variants successfully reproduce under the environmental conditions.

Question 14

A beetle population includes heritable variation in enzyme activity: allele H produces a heat-stable enzyme, while allele h produces a heat-sensitive enzyme. After a regional heat wave each summer, beetles with heat-sensitive enzymes survive to reproduce at lower rates. If heat waves continue for many generations, which outcome is most likely in the population?

Allele h will increase because surviving beetles will acquire heat tolerance during their lifetimes.
Allele H will increase in frequency because carriers contribute more offspring after heat waves. (correct answer)
Both alleles will remain at the same frequency because temperature does not affect reproduction.
Allele H will disappear because selection always removes rare alleles from populations.
The population will produce heat-stable enzymes because beetles are exposed to higher temperatures.

Explanation: This question examines natural selection acting on enzyme function under environmental stress. The correct answer is B because beetles with the H allele (heat-stable enzyme) survive heat waves at higher rates and therefore reproduce more successfully than beetles with the h allele. Over many generations of heat waves, the H allele will increase in frequency as its carriers contribute disproportionately more offspring to each subsequent generation. Answer A incorrectly suggests that individual beetles can acquire heat tolerance during their lifetime and pass it on, which confuses learned traits with inherited ones. When analyzing natural selection problems, focus on which heritable variants leave more offspring under the given environmental conditions.

Question 15

In a fish population, some individuals have a heritable allele that produces a larger tail fin, while others have smaller fins. A new predator is introduced that more easily catches fish with larger fins, and small-finned fish survive and reproduce more often. Tail-fin size variation persists among juveniles. Which outcome is most likely after many generations?

The allele for smaller fins will increase in frequency because those fish leave more offspring. (correct answer)
Fish with large fins will learn to avoid predators, so large-fin alleles will increase.
Allele frequencies will not change because predators remove fish regardless of genotype.
The population will gain the small-fin allele because predators induce mutations in survivors.
Large-fin alleles will increase because fewer large-finned fish survive, reducing intraspecific competition.

Explanation: This question tests understanding of natural selection, the process where heritable traits that enhance survival and reproduction become more common in a population over generations. The new predator catches large-finned fish more easily, allowing small-finned fish to survive and reproduce more often. Consequently, small-finned fish pass on more alleles for smaller fins, increasing their frequency in the population over generations. This occurs through differential survival and reproduction favoring the small-fin trait, with variation persisting among juveniles. A tempting distractor is choice B, which incorrectly assumes fish learn to avoid predators and pass this behavior genetically, confusing learned behaviors with heritable traits. For natural selection questions, always identify the selective pressure, the heritable trait, and how it affects reproductive success at the population level.

Question 16

A population of flowering plants shows heritable variation in nectar volume: high-nectar and low-nectar. In a region where a pollinator species becomes more abundant, plants with higher nectar volume receive more visits and set more seeds than low-nectar plants. Both nectar types still occur among seedlings. Which outcome is most likely over generations in this region?

Low-nectar alleles will increase because low-nectar plants conserve resources and reproduce more.
High-nectar plants will increase nectar production during their lives, raising high-nectar alleles.
High-nectar alleles will increase because plants with that trait contribute more seeds to the next generation. (correct answer)
Allele frequencies will remain constant because pollinator abundance does not affect plant reproduction.
The population will stop showing nectar variation because increased pollination prevents recombination.

Explanation: This question tests understanding of natural selection, the process where heritable traits that enhance survival and reproduction become more common in a population over generations. With more abundant pollinators, high-nectar plants receive more visits and set more seeds, giving them a reproductive edge over low-nectar plants. As a result, high-nectar plants contribute more offspring, leading to an increase in high-nectar alleles at the population level. This selection favors attractive traits in the pollinator-rich environment, even though both types appear among seedlings. A tempting distractor is choice B, which wrongly claims plants increase nectar production individually and inheritably, reflecting the misconception of Lamarckian inheritance. For natural selection questions, always identify the selective pressure, the heritable trait, and how it affects reproductive success at the population level.

Question 17

A population of mice has heritable variation in coat pattern: spotted or solid. In a habitat where snow cover decreases, the background becomes mostly dark soil, and predators capture spotted mice more often than solid mice. Solid-pattern mice survive and reproduce at higher rates, though both patterns still appear among pups. Which outcome is most likely over time?

Spotted-pattern alleles will increase because predation removes spotted mice and reduces competition.
Mice will change to solid coats within their lifetimes, so solid alleles will spread rapidly.
Solid-pattern alleles will increase in frequency because solid mice contribute more offspring. (correct answer)
Allele frequencies will remain constant because both coat patterns continue to appear each generation.
Spotted-pattern alleles will become fixed because spotted mice are more visible and thus more likely to mate.

Explanation: This question tests understanding of natural selection, the process where heritable traits that enhance survival and reproduction become more common in a population over generations. Decreased snow cover exposes dark soil, making spotted mice more visible to predators, while solid-pattern mice blend in and reproduce more. Consequently, solid-pattern mice pass on more alleles for solid coats, increasing their frequency in the population over time. This camouflage-driven selection favors the solid trait, even as both patterns appear among pups. A tempting distractor is choice B, which wrongly suggests mice change coats individually and inheritably, illustrating the misconception of Lamarckian evolution. For natural selection questions, always identify the selective pressure, the heritable trait, and how it affects reproductive success at the population level.

Question 18

In a lizard population, some individuals have a heritable allele for longer hind limbs, while others have shorter limbs. After a hurricane increases open sandy habitat, longer-limbed lizards run faster on sand and produce more offspring than shorter-limbed lizards. Limb-length variation remains among hatchlings. Which outcome is most likely over time in this population?

Alleles for longer hind limbs will increase in frequency because those individuals contribute more offspring. (correct answer)
Short-limbed lizards will grow longer limbs from exercise, increasing long-limb allele frequency.
Allele frequencies will not change because running speed is an acquired trait, not genetic.
Short-limb alleles will increase because fewer short-limbed lizards survive, reducing competition.
The population will become entirely long-limbed in one generation because selection removes all short-limb alleles.

Explanation: This question tests understanding of natural selection, the process where heritable traits that enhance survival and reproduction become more common in a population over generations. The hurricane creates more open sandy habitat where longer-limbed lizards run faster and produce more offspring than shorter-limbed ones. Thus, longer-limbed lizards contribute more descendants, increasing the frequency of long-limb alleles in the population. This directional shift favors speed in the new habitat, with variation remaining among hatchlings. A tempting distractor is choice B, which incorrectly suggests short-limbed lizards grow longer limbs from exercise and pass this on, embodying the misconception of acquired characteristics being heritable. For natural selection questions, always identify the selective pressure, the heritable trait, and how it affects reproductive success at the population level.

Question 19

A grass population includes individuals with either high or low waxy leaf coating. The coating level is heritable. During a multi-year drought, plants with higher waxy coating lose less water and produce more seeds than plants with low coating. Seedlings each year show both coating types. Which outcome is most likely after several drought years?

Low-coating plants will increase wax production during drought, raising high-coating allele frequency.
High-coating alleles will become more common because plants with that trait contribute more seeds. (correct answer)
Allele frequencies will not change because drought affects all plants equally within a generation.
The grass population will stop showing variation in coating because drought eliminates mutation.
Low-coating alleles will increase because fewer low-coating plants survive, reducing density.

Explanation: This question tests understanding of natural selection, the process where heritable traits that enhance survival and reproduction become more common in a population over generations. During the drought, plants with higher waxy leaf coating lose less water and produce more seeds, giving them a reproductive advantage over low-coating plants. Consequently, high-coating plants contribute more offspring to subsequent generations, increasing the frequency of high-coating alleles in the population. This shift occurs because natural selection favors the trait that improves fitness under drought conditions, with variation persisting among seedlings. A tempting distractor is choice A, which wrongly implies that individual plants adapt by increasing wax production during their lifetimes and pass this on, embodying the misconception of inheritance of acquired characteristics. For natural selection questions, always identify the selective pressure, the heritable trait, and how it affects reproductive success at the population level.

Question 20

A beetle population varies in body color, a heritable trait controlled by alleles G (green) and g (brown). In a forest, birds preferentially capture green beetles when leaves are absent during a prolonged drought, because green beetles are more visible on brown branches and leaf litter. Brown beetles are less often captured and more frequently survive to reproduce. The population remains in the same area and continues interbreeding. Which outcome is most likely after several generations of drought?

Allele G increases because green beetles can photosynthesize and gain extra energy for reproduction.
Allele frequencies remain unchanged because predation does not affect which beetles reproduce.
Allele g increases because brown beetles leave more offspring than green beetles under drought conditions. (correct answer)
Individual green beetles become brown during the drought and pass that color change to offspring.
Both alleles become equally common because visibility differences cause random mating among colors.

Explanation: This question tests understanding of natural selection, the process where heritable traits that improve survival and reproduction become more common in a population over generations. During drought, green beetles with allele G are more visible and captured by birds more often, while brown beetles with allele g are camouflaged, survive better, and reproduce more. This results in an increase in the frequency of allele g, as brown beetles contribute more offspring inheriting the brown color. The population-level shift occurs because the selective pressure of predation favors the brown trait in the altered environment. A tempting distractor is choice D, which suggests individual beetles change color and pass it on, illustrating the misconception of acquired trait inheritance. For natural selection questions, always identify the environmental pressure, the heritable variation it acts on, and how it leads to changes in allele frequencies through differential reproduction.