CUET UG Biology Booster Test 3 Adaptive Radiation and Population Genetics -

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CUET UG Biology Booster Test 3 Adaptive Radiation and Population Genetics

⏱️ 30 Minutes

❓ 20 Questions

📌 Answers are locked once submitted — results and explanations appear at the end.

CUET UG Biology Booster Test 3 Adaptive Radiation and Population Genetics

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QUESTION 1 OF 20

Match the evolutionary concept with its corresponding role:

List I	List II
1. Built-in variation	a. Enabled finches to radiate into vegetarian and insectivorous forms
2. Adaptive radiation	b. Formed the basis for varying characteristics within a population
3. Common ancestor	c. Gave rise to multiple species adapted to different ecological niches
4. Natural selection	d. Favoured individuals best suited to their environment

Answer Review

1 Match the evolutionary concept with its corresponding role:

List I	List II
1. Built-in variation	a. Enabled finches to radiate into vegetarian and insectivorous forms
2. Adaptive radiation	b. Formed the basis for varying characteristics within a population
3. Common ancestor	c. Gave rise to multiple species adapted to different ecological niches
4. Natural selection	d. Favoured individuals best suited to their environment

A 1-b, 2-a, 3-c, 4-d

B 1-a, 2-b, 3-d, 4-c

C 1-c, 2-d, 3-a, 4-b

D 1-d, 2-c, 3-b, 4-a

💡 Short Explanation

Built-in variation provides the raw material for evolution. Adaptive radiation results in diversification into different ecological niches. A common ancestor gives rise to related species. Natural selection favours individuals with advantageous traits.

✅ Correct Answer Explanation

The correct matching is: According to NCERT, built-in variation among individuals provides the raw material on which evolution acts. Adaptive radiation is the evolution of different species from a common ancestor to occupy diverse ecological niches, as seen in Darwin's finches on the Galápagos Islands. These finches evolved different beak types suited to various food sources such as seeds, insects, and vegetation. Natural selection preserves favourable variations, leading to the survival and reproduction of the fittest individuals. Therefore, the correct matching is 1-b, 2-a, 3-c, 4-d.

❓ Why Other Options Are Incorrect

Option B → Incorrectly reverses the roles of built-in variation and adaptive radiation.
Option C → Incorrectly matches common ancestor and natural selection.
Option D → Misaligns all the evolutionary concepts with their functions.

🎯 Strategy

Used: Concept Matching

Application: Associate each evolutionary concept with its specific role in Darwin's explanation of adaptive radiation.

Final Logic:

Variation → Raw material
Adaptive radiation → Diversification
Common ancestor → Origin of related species
Natural selection → Survival of the fittest

🧠 Memory Trick

"Variation Begins, Radiation Branches, Ancestor Starts, Selection Sustains."

📚 Class XII – Biology – Chapter: Evolution – Topic: Adaptive Radiation and Natural Selection

2 The rapid evolution of multiple beak types in Darwin's finches starting from a single seed-eating ancestor is the evolutionary consequence of which Darwinian principle?

A Saltation

B Better resource utilization leading to higher reproductive fitness

C The spontaneous generation of forms

D Intentional mutation by the organism

💡 Short Explanation

Natural selection favors individuals who utilize resources efficiently. Resource competition drives niche specialization (beak types). Fitness increases in new niches, leading to speciation.

✅ Correct Answer Explanation

Darwin's theory of natural selection is centered on competition. When finches faced competition for seeds, those with beak variations capable of exploiting other resources (insects, fruits) had better survival and reproductive success. This is a classic example of adaptive radiation driven by competitive exclusion and resource partitioning.

❓ Why Other Options Are Incorrect

Option A → Saltation is De Vries' theory of single-step large mutations, not gradual adaptive radiation.
Option C → Spontaneous generation is a disproven theory of life's origin, not evolution.
Option D → Mutations are random, not "intentional" acts by the organism.

🎯 Strategy

Used: Elimination

Application: Options A, C, and D are scientifically incorrect or irrelevant to Darwinian natural selection principles.

Final Logic: Natural selection is driven by survival and reproductive fitness based on niche exploitation.

🧠 Memory Trick

"Darwin = Survival of the fittest" through "Resource utilization."

📚 Class XII – Biology – Chapter: Evolution – Topic: Adaptive Radiation

3 Which of the following statements does NOT correctly describe the geographical necessity for adaptive radiation?

A It requires a starting point from which radiation occurs.

B It depends on the migration of an organism across globally connected mega-continents.

C It involves radiating into different habitats within a given geographic area.

D It can occur multiple times in an isolated geographical area.

💡 Short Explanation

Adaptive radiation usually requires isolation or distinct niches, not necessarily migration across "connected mega-continents." Continental connection usually leads to homogenization, not radiation. Radiation is most successful in isolated areas (e.g., Galapagos, Australia).

✅ Correct Answer Explanation

Adaptive radiation is the development of many species from a common ancestor in a specific geographic area (like an island). Migration across connected continents would likely lead to competition or interbreeding, not the specific habitat-driven radiation seen in isolated environments.

❓ Why Other Options Are Incorrect

Option A → A starting point (ancestor) is essential for radiation.
Option C → Occupying different habitats is the definition of the process.
Option D → Repeated radiations can occur in isolated clusters.

🎯 Strategy

Used: Extreme Word Filter

Application: The phrase "globally connected mega-continents" contrasts sharply with the "isolated" or "niche-specific" nature of radiation.

Final Logic: Isolation is the primary driver; connection is the opposite of isolation.

🧠 Memory Trick

"Radiation needs Isolation": Keep them apart to evolve apart.

📚 Class XII – Biology – Chapter: Evolution – Topic: Adaptive Radiation

4 Analytically speaking, if two distinct ancestral lines undergo adaptive radiation in the same isolated geography but occupy similar ecological niches, the end result is termed:

A Genetic equilibrium

B Branching descent

C Convergent evolution

D Founder effect

💡 Short Explanation

Different ancestors (distinct lines). Same environment/niche. Similar adaptations = Convergent evolution.

✅ Correct Answer Explanation

When different species (from different ancestors) evolve similar traits to suit the same ecological niche, it is known as convergent evolution. This is distinct from adaptive radiation, which describes how one ancestor becomes many species.

❓ Why Other Options Are Incorrect

Option A → Genetic equilibrium refers to Hardy-Weinberg stability.
Option B → Branching descent is the result of adaptive radiation from one ancestor.
Option D → Founder effect refers to the loss of genetic variation in a new, small population.

🎯 Strategy

Used: Substitution

Application: Substitute "distinct ancestral lines" + "same niche" with the classic example: "Placental and Marsupial mammals." This equates to convergent evolution.

Final Logic: Convergent evolution is defined by different origins + similar end-points.

🧠 Memory Trick

"Convergent = Coming together" in form, despite starting apart.

📚 Class XII – Biology – Chapter: Evolution – Topic: Convergent Evolution

5 Arrange the factors that sequentially led to the modern diversity of Australian marsupials:
I. Separation of the Australian landmass (Continental drift).
II. Adaptive radiation within different habitats.
III. Survival and divergence due to lack of placental mammal competition.
IV. Presence of a single ancestral marsupial stock.

A IV → I → III → II

B I → IV → II → III

C IV → I → II → III

D I → III → IV → II

💡 Short Explanation

Step 1: Start with the ancestor (IV). Step 2: Isolate the area via drift (I). Step 3: Lack of competition allows survival (III). Step 4: Diversify into niches (II).

✅ Correct Answer Explanation

First, you must have an ancestral stock (IV). Then, the separation of Australia (I) acts as the catalyst for isolation. In this isolation, because placental mammals are absent (III), the marsupials are free to fill all ecological niches, leading to adaptive radiation (II).

❓ Why Other Options Are Incorrect

Options B, C, D → Misorder the causal flow of the evolutionary process.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Logically order the evolutionary narrative: Ancestor -> Barrier -> Niche freedom -> Diversification.

Final Logic: Evolution requires an ancestor, a barrier, and then a mechanism for diversification.

🧠 Memory Trick

"A-I-S-D" (Ancestor, Isolation, Survival, Diversification).

📚 Class XII – Biology – Chapter: Evolution – Topic: Adaptive Radiation

6 Consider the following statements regarding geographical isolation and evolution:
Statement I: The isolated geographical development of Australia prevented placental mammals from out-competing marsupials.
Statement II: Australian marsupials underwent adaptive radiation identically to placental mammals in South America.

A Statement I is correct, Statement II is incorrect.

B Statement I is incorrect, Statement II is correct.

C Both statements are correct.

D Both statements are incorrect.

💡 Short Explanation

Statement I: Correct, isolation is the reason marsupials exist today. Statement II: Incorrect, the radiation was parallel (convergent), but not "identical" (different groups).

✅ Correct Answer Explanation

Statement I is accurate: isolation provided a refuge. Statement II is incorrect because marsupials and placentals are different groups; while they show convergent evolution, their evolutionary pathways and developmental mechanisms are unique to their respective groups.

❓ Why Other Options Are Incorrect

Option B → Incorrectly labels Statement I as false.
Option C → Incorrectly assumes identical evolutionary pathways.
Option D → Incorrectly assumes both are false.

🎯 Strategy

Used: Elimination

Application: Statement I is a foundational evolutionary fact (True). Statement II claims "identically," which is a hallmark of false absolute statements in biology.

Final Logic: T + F = A.

🧠 Memory Trick

"Identical = Impossible in evolution."

📚 Class XII – Biology – Chapter: Evolution – Topic: Adaptive Radiation

7 Based on Figure, the parallel evolution of forms like the flying squirrel and the flying phalanger exemplifies:

A How genetic drift uniquely shapes un-related populations.

B How different evolutionary lines converge upon similar adaptations in similar habitats.

C The founder effect dominating island populations.

D The disruption of Hardy-Weinberg equilibrium by migration.

💡 Short Explanation

Flying squirrel (Placental) and Flying phalanger (Marsupial) are different lines. They share similar adaptations (gliding). This is the definition of convergent evolution.

✅ Correct Answer Explanation

This is the textbook example of convergent evolution. Two different subclasses of mammals (Placentals and Marsupials) evolved to solve the same ecological problem (getting around in trees) using the same solution (gliding), proving that similar selective pressures lead to similar morphologies.

❓ Why Other Options Are Incorrect

Option A → Genetic drift is a random change, not a selective adaptation.
Option C → Founder effect is about the genetic bottleneck at colonization.
Option D → Migration does not explain the convergent morphological similarity.

🎯 Strategy

Used: Substitution

Application: The "flying squirrel vs. phalanger" example is the standard visual aid for Convergent Evolution in NCERT.

Final Logic: Different lineages + Similar environment = Convergence.

🧠 Memory Trick

"Squirrel vs. Phalanger = Convergent Pair."

📚 Class XII – Biology – Chapter: Evolution – Topic: Convergent Evolution

8 According to Figure, the Tasmanian wolf (a marsupial) demonstrates morphological similarities to the placental wolf. This similarity indicates that they:

A Share an immediate common ancestor from the recent past.

B Frequently interbred prior to continental drift.

C Evolved analogous characteristics due to similar selective pressures.

D Resulted from a single point of origin radiating into different habitats.

💡 Short Explanation

Tasmanian wolf and placental wolf are not closely related (analogous). Similar niches create similar body shapes (selective pressure). This is the definition of analogy in convergent evolution.

✅ Correct Answer Explanation

These organisms are unrelated; their similarity is "analogous" (similar function/shape, different underlying structure). This occurs because they both function as predators in their respective environments, subjecting them to the same evolutionary "selective pressures."

❓ Why Other Options Are Incorrect

Option A → They are very distant relatives (Marsupials vs Placentals diverged long ago).
Option B → They were separated by continental drift.
Option D → Adaptive radiation from a single ancestor would mean they are related, which they are not.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: The term "analogous" is the key to identifying evolution in distant groups.

Final Logic: Analogous = Different origin, similar function (convergent).

🧠 Memory Trick

"Analogous = Adapted" (by pressure, not by blood).

📚 Class XII – Biology – Chapter: Evolution – Topic: Convergent Evolution (Homology/Analogy)

9 Match the Hardy–Weinberg algebraic component with its biological representation in a diploid population.

List I	List II
1. p²	a. Homozygous recessive genotype (aa)
2. 2pq	b. Homozygous dominant genotype (AA)
3. q²	c. Heterozygous genotype (Aa)
4. p + q	d. Sum of allele frequencies

A 1-b, 2-c, 3-a, 4-d

B 1-c, 2-a, 3-d, 4-b

C 1-a, 2-d, 3-b, 4-c

D 1-b, 2-d, 3-c, 4-a

💡 Short Explanation

p² represents the frequency of homozygous dominant individuals. 2pq represents the frequency of heterozygotes. q² represents the frequency of homozygous recessive individuals. p + q = 1 represents the total allele frequency.

✅ Correct Answer Explanation

The Hardy–Weinberg principle states that in a large, randomly mating population with no mutation, migration, natural selection, or genetic drift, allele frequencies remain constant from generation to generation. The equilibrium is expressed as: (p + q)² = p² + 2pq + q² = 1

❓ Why Other Options Are Incorrect

Option B → Incorrectly assigns genotype frequencies to the wrong algebraic terms.
Option C → Incorrectly matches allele frequency and genotype frequency.
Option D → Incorrectly associates heterozygous and recessive genotype frequencies.

🎯 Strategy

Used: Formula Interpretation

Application: Interpret each term of the Hardy–Weinberg equation biologically.

Final Logic:

p² → AA
2pq → Aa
q² → aa
p + q → Total allele frequency

🧠 Memory Trick

p + q = Sum of Alleles

📚 Class XII – Biology – Chapter: Evolution – Topic: Hardy–Weinberg Principle

10 Which of the following is NOT a true implication if the allele frequencies in a population consistently equal 1 (i.e., (p^2 + 2pq + q^2 = 1)) and match expected values exactly?

A The population is in genetic equilibrium.

B Evolutionary change is actively taking place.

C The gene pool remains constant from generation to generation.

D Natural selection and genetic drift are not causing observable shifts.

💡 Short Explanation

Equilibrium means no change. If frequencies match expected values, no evolution is happening. Statement B claims change is happening, which contradicts equilibrium.

✅ Correct Answer Explanation

When Hardy-Weinberg conditions are met, the allele frequencies and genotype frequencies remain constant. If they remain constant, evolution is not occurring. Thus, claiming evolution is "actively taking place" is false.

❓ Why Other Options Are Incorrect

Option A → The math confirms the equilibrium.
Option C → "Constant gene pool" is the definition of H-W.
Option D → If natural selection/drift were active, the frequencies would shift, violating the equilibrium.

🎯 Strategy

Used: Elimination

Application: Look for the statement that contradicts the definition of equilibrium. B is the direct contradiction.

Final Logic: Equilibrium = Static = No Evolution.

🧠 Memory Trick

"H-W Equilibrium = No Evolution."

📚 Class XII – Biology – Chapter: Evolution – Topic: Hardy-Weinberg Principle

11 Arrange the steps used to deduce evolutionary change using Hardy-Weinberg algebraic foundations:
I. Calculate the expected genotypic frequencies using ((p+q)^2 = 1).
II. Measure the actual frequency of alleles and genotypes in the given population.
III. Interpret the difference (direction) between measured and expected values.
IV. Determine the extent of evolutionary change.

A I → II → III → IV

B II → I → III → IV

C II → III → I → IV

D I → III → II → IV

💡 Short Explanation

First, collect real-world data (II). Second, calculate the theoretical H-W expectation (I). Third, compare them (III). Fourth, conclude how much the population has evolved (IV).

✅ Correct Answer Explanation

To identify evolutionary change, you must first establish the "actual" (measured) state of the population (II). You then use the H-W model to calculate what the population would look like if it were in equilibrium (I). By comparing the difference between actual and expected (III), you can quantitatively determine the extent of the deviation, which equates to the magnitude of evolutionary change (IV).

❓ Why Other Options Are Incorrect

Option A → Starting with calculation (I) before having actual population data (II) is impossible.
Option C → Interpreting differences (III) before calculating the expectation (I) is illogical.
Option D → Again, places the theory (I) before the observation (II).

🎯 Strategy

Used: Substitution

Application: Follow the scientific method: Observation -> Model -> Comparison -> Conclusion.

Final Logic: Real-world observation (II) must precede theoretical calculation (I).

🧠 Memory Trick

"Observe -> Predict -> Compare -> Conclude."

📚 Class XII – Biology – Chapter: Evolution – Topic: Hardy-Weinberg Principle

12 If the frequency of allele A ((p)) is 0.6 and allele a ((q)) is 0.4, the mathematical difference between the expected frequency of the heterozygous genotype and the homozygous recessive genotype is: (Note: Application of (2pq) vs (q^2))

A 0.48 - 0.16 = 0.32

B 0.36 - 0.16 = 0.20

C 0.48 - 0.36 = 0.12

D 0.24 - 0.16 = 0.08

💡 Short Explanation

p = 0.6, q = 0.4. Heterozygous frequency (2pq) = 2 × 0.6 × 0.4 = 0.48. Homozygous recessive frequency (q²) = 0.4 × 0.4 = 0.16. Difference = 0.48 − 0.16 = 0.32.

✅ Correct Answer Explanation

Using the Hardy–Weinberg formula, 2pq = 2 × 0.6 × 0.4 = 0.48. The homozygous recessive genotype frequency is q² = 0.4 × 0.4 = 0.16. Therefore, the required difference is: 2pq − q² = 0.48 − 0.16 = 0.32.

❓ Why Other Options Are Incorrect

Option B, C, and D → Represent incorrect calculations of 2pq or q².

🎯 Strategy

Used: Dimensional/Unit Analysis

Application: Apply the algebra directly: p = 0.6 and q = 0.4. Then, 2(0.6)(0.4) = 0.48 and (0.4)² = 0.16. Subtracting gives 0.32.

Final Logic: Precise application of H-W values confirms A.

🧠 Memory Trick

"2pq = 0.48, q^2 = 0.16": Simple multiplication.

📚 Class XII – Biology – Chapter: Evolution – Topic: Hardy-Weinberg (Numerical application)

13 Consider the following statements about gene migration:
Statement I: Migration uniquely alters the allele frequency of the new population while maintaining the exact allele frequencies of the old population.
Statement II: If gene migration happens multiple times, it creates a constant gene flow between populations.

A Only Statement I is correct.

B Only Statement II is correct.

C Both Statement I and II are correct.

D Neither Statement I nor II are correct.

💡 Short Explanation

Statement I: False, migration changes allele frequencies in both the donor and recipient populations (gene pool shifts). Statement II: True, repeating migration equals continuous gene flow.

✅ Correct Answer Explanation

Statement I is incorrect because migration involves moving individuals (and their alleles) out of one group and into another. This loss in the old population must change its allele frequency. Statement II is correct: frequent migration between two populations is the literal definition of continuous gene flow.

❓ Why Other Options Are Incorrect

Option A → Incorrectly validates Statement I.
Option C → Incorrectly assumes migration doesn't affect the donor.
Option D → Fails to acknowledge the accuracy of Statement II.

🎯 Strategy

Used: Elimination

Application: Analyze Statement I: Does moving people out affect the source? Yes, it changes the ratio. Therefore I is false. Eliminate A and C.

Final Logic: If I is false and II is logically sound, B is the only path.

🧠 Memory Trick

"Migration = Change for both sides."

📚 Class XII – Biology – Chapter: Evolution – Topic: Gene Flow/Migration

14 Which of the following conditions is NOT associated with the continuous process of gene flow?

A Repeated migration of a section of a population.

B Gradual homogenization of gene frequencies between two populations.

C The strict isolation of the population leading to a highly static gene pool.

D Addition of new genes/alleles to a receiving population over time.

💡 Short Explanation

Gene flow is the mixing of populations. Strict isolation is the prevention of gene flow. C describes the opposite of gene flow.

✅ Correct Answer Explanation

Gene flow acts to homogenize populations (make them more similar) by transferring alleles. Strict isolation prevents this transfer, keeping the gene pool static. Therefore, C is fundamentally incompatible with the concept of gene flow.

❓ Why Other Options Are Incorrect

Option A, B, D → These are all direct characteristics/consequences of gene flow.

🎯 Strategy

Used: Odd One Out

Application: A, B, and D all describe "moving/mixing" (flow). C describes "staying still" (isolation).

Final Logic: Isolation contradicts Flow.

🧠 Memory Trick

"Flow = Mixing; Isolation = Static."

📚 Class XII – Biology – Chapter: Evolution – Topic: Gene Flow

📄 Passage

"If the same change occurs by chance, it is called genetic drift. Sometimes the change in allele frequency is so different in the new sample of population that they become a different species. The original drifted population becomes founders and the effect is called founder effect."

According to the passage, the primary distinguishing mechanism of genetic drift compared to natural selection is that genetic drift:

A Is driven purely by chance rather than reproductive fitness.

B Only occurs in populations experiencing extreme gene flow.

C Always prevents the formation of a different species.

D Requires a highly specific habitat to function.

💡 Short Explanation

Natural selection = Adaptive, fitness-based. Genetic drift = Stochastic, chance-based. The passage defines drift as "happening by chance."

✅ Correct Answer Explanation

The passage explicitly states, "If the same change occurs by chance, it is called genetic drift." Natural selection, by contrast, is not random; it selects for traits that enhance survival and reproduction.

❓ Why Other Options Are Incorrect

Option B → Genetic drift is more common in small populations, often isolated, not necessarily high gene flow.
Option C → The passage states drift can lead to new species.
Option D → Genetic drift is habitat-independent.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Match the passage's definition ("by chance") with Option A.

Final Logic: Chance = Drift; Fitness = Selection.

🧠 Memory Trick

"Drift = Luck (Chance); Selection = Skill (Fitness)."

📚 Class XII – Biology – Chapter: Evolution – Topic: Genetic Drift

📄 Passage

Based on the passage, the classification of the original drifted population as "founders" implies that:

A They perfectly mirror the ancestral gene pool without deviation.

B The chance changes in their allele frequencies became the baseline for a new species.

C They interbred heavily with the original population.

D They stabilized the Hardy-Weinberg equilibrium.

💡 Short Explanation

Founder effect = A small group starts a new population. Their limited allele set becomes the "new normal." This facilitates speciation (as noted in the passage).

✅ Correct Answer Explanation

The passage states, "The original drifted population becomes founders... change in allele frequency is so different... they become a different species." This means the unique, chance-driven allele mix of this small group acts as the genetic foundation for the emerging species.

❓ Why Other Options Are Incorrect

Option A → Drift creates deviation, it does not mirror the original exactly.
Option C → Founders are usually geographically or reproductively isolated, preventing interbreeding.
Option D → Drift disrupts H-W equilibrium; it doesn't stabilize it.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Look at the passage's concluding sentence linking "founders" to "different species."

Final Logic: Founders create the baseline for the new group.

🧠 Memory Trick

"Founder = New Baseline."

📚 Class XII – Biology – Chapter: Evolution – Topic: Founder Effect

17 Analytically, stabilizing selection acts to restrict evolutionary change by:

A Continually shifting the population mean in response to environmental chance.

B Favoring individuals with the mean character value and selecting against peripheral variations.

C Disrupting the gene pool and promoting extreme variations.

D Eliminating the mean character value entirely.

💡 Short Explanation

Stabilizing selection = "Middle is best." It eliminates extremes (too big/too small). Result: Population stays at the mean.

✅ Correct Answer Explanation

Stabilizing selection is a mode of natural selection that reduces variation. It selects against the extremes (periphery) and supports the central phenotype (the mean), effectively preventing significant shifts in the population mean.

❓ Why Other Options Are Incorrect

Option A → Describes directional selection.
Option C → Describes disruptive selection.
Option D → Describes disruptive selection (selecting against the mean).

🎯 Strategy

Used: Substitution

Application: Substitute "Stabilizing" with "Average-supporting."

Final Logic: Stabilizing = Selecting the average.

🧠 Memory Trick

"Stabilizing = Sticking to the middle."

📚 Class XII – Biology – Chapter: Evolution – Topic: Natural Selection (Modes)

18 Which of the following is NOT true regarding disruptive selection?

A It splits the population into two major phenotypic groups.

B It results in more individuals acquiring peripheral character values.

C It occurs when individuals at both ends of the distribution curve are favored.

D It leads to the vast majority of the population converging strictly on the mean character value.

💡 Short Explanation

Disruptive selection = "Extremes are best." Mean is selected against. D describes stabilizing selection, not disruptive.

✅ Correct Answer Explanation

Disruptive selection favors both ends of the spectrum and selects against the mean. Therefore, saying it leads to convergence on the mean is the opposite of the truth.

❓ Why Other Options Are Incorrect

Option A, B, C → These are all true descriptions of the disruptive process.

🎯 Strategy

Used: Extreme Word Filter

Application: Disruptive selection disrupts the mean, so D is clearly the incorrect statement requested by the question.

Final Logic: Disruptive = Extremes; Stabilizing = Mean.

🧠 Memory Trick

"Disruptive = Split the middle."

📚 Class XII – Biology – Chapter: Evolution – Topic: Natural Selection (Modes)

19 While genetic recombination generates variations, how does natural selection ultimately interface with these variations to produce a seemingly "different population"?

A By ensuring all variations randomly survive.

B By systematically mutating all variations back to the mean.

C By coupling these variations with enhanced reproductive success.

D By migrating the variants to an isolated continent.

💡 Short Explanation

Recombination = Source of raw variety. Selection = Sieve that chooses variety. Selection works by promoting survival and reproduction of specific variants.

✅ Correct Answer Explanation

Natural selection acts as the filter. It works by identifying which variations (generated by recombination) provide a survival or reproductive advantage, effectively increasing the frequency of those specific variants in the next generation.

❓ Why Other Options Are Incorrect

Option A → Random survival is drift, not selection.
Option B → Mutations/recombination aren't "mutated back."
Option D → Migration is gene flow, not natural selection.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Select the option that defines Natural Selection (Differential reproductive success).

Final Logic: Variation + Reproductive Advantage = Selection.

🧠 Memory Trick

"Selection = Success."

📚 Class XII – Biology – Chapter: Evolution – Topic: Natural Selection

20 According to the perspectives of early 20th-century population genetics, why did Hugo deVries refer to mutation-driven speciation as "saltation"?

A Because he believed evolution was gradual and based on minor directional variations.

B Because he posited that a single step large mutation causes speciation randomly and directionlessly.

C Because mutations always lead directly to genetic equilibrium.

D Because mutations strictly rely on crossing over during gametogenesis.

💡 Short Explanation

De Vries' Mutation Theory = "Saltation" (Leaping). Evolution happens in big jumps (mutations), not small steps. These are random and large.

✅ Correct Answer Explanation

Hugo de Vries believed that evolution was not gradual. He coined "saltation" (meaning "jump" or "leap") to explain his view that a single, large-scale mutation could suddenly create a new species in one generation.

❓ Why Other Options Are Incorrect

Option A → Darwin proposed gradualism; De Vries opposed it.
Option C → Mutations disrupt, not create, equilibrium.
Option D → Crossing over is recombination; mutations are distinct events.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Recall the term "Saltation" = "Leaping/Jump" in evolutionary context.

Final Logic: Saltation = Large, sudden change.

🧠 Memory Trick

"Saltation = Saltare (Latin for 'to jump') = Mutation Leap."

📚 Class XII – Biology – Chapter: Evolution – Topic: Mutation Theory

CUET UG Biology Booster Test 3 Adaptive Radiation and Population Genetics

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