CUET UG Biology Booster Test 3 Mendelian Foundations -

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CUET UG Biology Booster Test 3 Mendelian Foundations

⏱️ 30 Minutes

❓ 20 Questions

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

CUET UG Biology Booster Test 3 Mendelian Foundations

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QUESTION 1 OF 20

Analyze the relationship between inheritance and variation. Which statement best represents their connection?

Answer Review

1 Analyze the relationship between inheritance and variation. Which statement best represents their connection?

A Inheritance creates identity, while variation creates the degree of difference among progeny.

B Variation is the process of passing traits, while inheritance is the degree of difference.

C They are unrelated branches of biology studied independently by Mendel.

D Inheritance only applies to plants, while variation only applies to animals.

💡 Short Explanation

Inheritance ensures species continuity (offspring resemble parents). Variation introduces diversity (offspring differ from parents). Both are fundamental to the study of genetics.

✅ Correct Answer Explanation

Inheritance is the basis of heredity, ensuring that offspring share the fundamental characteristics of their species (identity). Variation is the degree to which progeny differ from their parents and each other. Option A accurately captures this duality, which forms the core of genetics.

❓ Why Other Options Are Incorrect

Option B → Reverses the definitions of inheritance and variation.
Option C → Mendel's work explicitly integrated both concepts.
Option D → Both phenomena apply to all sexually reproducing organisms, not specific kingdoms.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Match definitions with their conceptual roles in genetics.

Final Logic: Inheritance defines the "same-ness," while variation defines the "differences."

🧠 Memory Trick

Inherit = Identity; Variation = Variety.

📚 Class XII – Biology – Chapter: Principles of Inheritance and Variation – Topic: Introduction –

2 Why is sexual reproduction considered the hidden "cause" of variation in early human history?

A Because it prevents the blending of traits.

B Because it involves the segregation and recombination of factors.

C Because it was only discovered by Watson and Crick.

D Because it leads only to identical twins.

💡 Short Explanation

Sexual reproduction mixes parental genetic material. Segregation and recombination create new allelic combinations. These processes inherently lead to phenotypic differences.

✅ Correct Answer Explanation

Ancient humans linked sexual reproduction to variation because they observed that offspring from sexual matings consistently showed differences compared to their parents. Mechanistically, this is explained by the segregation of alleles during meiosis and the recombination of these alleles during fertilization, creating unique genotypes.

❓ Why Other Options Are Incorrect

Option A → Sexual reproduction does not prevent blending; Mendel proved that factors do not blend.
Option C → The link between sexual reproduction and variation was understood long before the DNA structure was discovered.
Option D → Sexual reproduction leads to genetic diversity, not identical clones (like identical twins).

🎯 Strategy

Used: Elimination

Application: Eliminate options that refer to modern discoveries (C) or scientifically inaccurate claims (A, D).

Final Logic: The biological basis of variation in sexual reproduction is the shuffling of alleles (recombination).

🧠 Memory Trick

Sex = Segregation + recombination = Variation.

📚 Class XII – Biology – Chapter: Principles of Inheritance and Variation – Topic: Introduction –

3 Match the aspect of Mendel's methodology with its scientific purpose:

List I	List II
1. Seven years of study	a. Verified general rules rather than unsubstantiated ideas
2. Large sampling size	b. Allowed for a basic framework of rules
3. Successive generations	c. Ensured reliability and persistence of patterns
4. Two opposing traits	d. Provided credibility to collected data

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

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

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

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

💡 Short Explanation

7 years = reliability of patterns (1-c). Large samples = statistical credibility (2-d). Successive generations = verification of rules (3-a). Opposing traits = framework for comparison (4-b).

✅ Correct Answer Explanation

Mendel's meticulous approach involved working for seven years (1856-1863) to ensure consistency (c). His large sample size provided the mathematical credibility required to minimize chance (d). Testing successive generations (F1, F2, F3) verified his proposed rules (a), and using contrasting trait pairs established the basic comparative framework for his experiments (b).

❓ Why Other Options Are Incorrect

Options B, C, and D misalign the purposes with the corresponding methodological steps.

🎯 Strategy

Used: Substitution

Application: Link "Large sampling" with "credibility" (2-d) and "7 years" with "reliability/persistence" (1-c) to isolate the correct combination.

Final Logic: The pairings in A correctly correlate experimental rigor with scientific outcomes.

🧠 Memory Trick

Large sample = Credible data.

📚 Class XII – Biology – Chapter: Principles of Inheritance and Variation – Topic: Mendel's Laws of Inheritance –

4 Which was NOT a reason for the initial scientific rejection of Mendel's approach?

A His concept of discrete factors contradicted the continuous variation seen in nature.

B The use of mathematics to explain biology was new and unacceptable.

C He failed to provide physical proof of the existence of factors.

D He used garden peas, which were known to be sterile.

💡 Short Explanation

Mendel's peas were fertile and perfect for hybridization. Rejection was due to mathematical complexity and lack of physical evidence. Option D is factually incorrect.

✅ Correct Answer Explanation

Mendel's use of garden peas was one of his greatest strengths because they were fertile, easy to cross-pollinate, and showed discrete traits. He was rejected because scientists did not understand his statistical approach, and he could not provide physical evidence (like microscopic observation) for his "factors."

❓ Why Other Options Are Incorrect

Option A → Scientists at the time believed only in continuous variation (e.g., Darwinism).
Option B → Mathematics was considered foreign in 19th-century biological studies.
Option C → The absence of cytological proof was a valid critique at the time.

🎯 Strategy

Used: Elimination

Application: Identify the clearly false statement regarding his experimental materials.

Final Logic: Pea plants are the model organism precisely because they are highly fertile and exhibit clear traits.

🧠 Memory Trick

Peas = Perfect, not sterile.

📚 Class XII – Biology – Chapter: Principles of Inheritance and Variation – Topic: Mendel's Laws of Inheritance –

5 How does continuous self-pollination result in a "true-breeding" line?

A It increases the frequency of heterozygous gene pairs.

B It ensures stable trait inheritance by maintaining homozygous allelic pairs.

C It causes the factors to blend more effectively.

D It allows the recessive traits to be masked indefinitely.

💡 Short Explanation

Selfing reduces heterozygosity. It purifies the line toward homozygosity. Homozygous lines are stable (true-breeding).

✅ Correct Answer Explanation

In a heterozygous individual (Tt), self-pollination results in a distribution of genotypes (TT, Tt, tt). Over successive generations of selfing, the frequency of heterozygotes (Tt) decreases by half each generation, while homozygotes (TT and tt) increase. This leads to the establishment of homozygous, "true-breeding" lines that pass traits faithfully.

❓ Why Other Options Are Incorrect

Option A → Selfing actually decreases heterozygosity.
Option C → Factors do not blend; blending is not a mechanism of stability.
Option D → True-breeding does not necessarily involve masking; it involves genetic purity.

🎯 Strategy

Used: Substitution

Application: Recall that homozygosity is the genetic state required for "true-breeding."

Final Logic: Selfing forces homozygosity; therefore, it purifies the trait inheritance.

🧠 Memory Trick

Selfing = Stability = Homozygosity.

📚 Class XII – Biology – Chapter: Principles of Inheritance and Variation – Topic: Mendel's Laws of Inheritance –

6 Mendel's selection of 14 varieties as "pairs" was analytical because:

A It allowed him to study the inheritance of one character with two contrasting traits.

B It proved that all traits are dominant.

C It was the only way to perform statistical analysis.

D It ensured that the F1 generation would show blending.

💡 Short Explanation

Mendel's rule: One character at a time. Contrasting traits allow for comparison. This is essential for observing dominant/recessive patterns.

✅ Correct Answer Explanation

Mendel's experimental success was largely due to his analytical approach of studying one character at a time. By selecting 14 true-breeding varieties as pairs of contrasting traits (e.g., tall/dwarf, round/wrinkled), he could isolate the inheritance pattern of each character without the interference of other traits.

❓ Why Other Options Are Incorrect

Option B → Not all traits are dominant; he identified recessive ones too.
Option C → Statistical analysis could be performed on single varieties, but "pairs" were needed for comparison.
Option D → He specifically rejected the blending hypothesis.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Recognize the definition of his "one character at a time" methodology.

Final Logic: Pairs permit the study of trait transmission between parents and offspring.

🧠 Memory Trick

Pairs = Contrasts = Clarity.

📚 Class XII – Biology – Chapter: Principles of Inheritance and Variation – Topic: Mendel's Laws of Inheritance –

7 Evaluate these pairs of contrasting traits:
I. Round seed is dominant over wrinkled seed.
II. Green pod color is dominant over yellow pod color.
III. Yellow seed color is dominant over green seed color.

A I and II are correct.

B II and III are correct.

C I, II, and III are correct.

D Only I is correct.

💡 Short Explanation

I: Round > Wrinkled (Correct). II: Green pod > Yellow pod (Correct). III: Yellow seed > Green seed (Correct).

✅ Correct Answer Explanation

All three statements accurately reflect Mendel's findings. Seed shape (Round) is dominant to Wrinkled; Pod color (Green) is dominant to Yellow; Seed color (Yellow) is dominant to Green. These are standard Mendelian findings documented in the NCERT table.

❓ Why Other Options Are Incorrect

Options A, B, and D exclude correct facts documented in Mendel's studies.

🎯 Strategy

Used: Elimination

Application: Review the NCERT table of traits to confirm dominance relationships.

Final Logic: All three listed relationships align perfectly with Mendel's experimental records.

🧠 Memory Trick

Remember: Green Pod = Dominant; Green Seed = Recessive.

📚 Class XII – Biology – Chapter: Principles of Inheritance and Variation – Topic: Mendel's Laws of Inheritance – (Table 5.1)

8 Which of the following character pairings studied by Mendel is NOT correctly matched with its dominant/recessive traits?

A Stem height: Tall (D) / Dwarf (R).

B Flower color: Violet (D) / White (R).

C Pod shape: Constricted (D) / Inflated (R).

D Seed shape: Round (D) / Wrinkled (R).

💡 Short Explanation

Inflated pod is dominant. Constricted pod is recessive. This option reverses the correct relationship.

✅ Correct Answer Explanation

In Mendel's experiments, the "Inflated" pod shape was dominant, and the "Constricted" pod shape was recessive. Therefore, pairing Constricted as dominant and Inflated as recessive is factually incorrect.

❓ Why Other Options Are Incorrect

Option A → Tall is indeed dominant to Dwarf.
Option B → Violet is indeed dominant to White.
Option D → Round is indeed dominant to Wrinkled.

🎯 Strategy

Used: Elimination

Application: Identify the reversed dominance relationship in the provided list.

Final Logic: Pod shape is the only mislabeled relationship here.

🧠 Memory Trick

Inflated (Full) = Dominant.

📚 Class XII – Biology – Chapter: Principles of Inheritance and Variation – Topic: Mendel's Laws of Inheritance –

9 Arrange these outcomes of a monohybrid cross by the frequency of their phenotypes in the F2 generation, from most frequent to least frequent:
1. Plants resembling the F1 parent.
2. Plants resembling the recessive parent.

A 1 (3/4), then 2 (1/4)

B 2 (3/4), then 1 (1/4)

C (option not parsed — please edit)

D (option not parsed — please edit)

💡 Short Explanation

F1 (Tall) is dominant. Dominant phenotype (F1-like) is 3/4. Recessive phenotype is 1/4.

✅ Correct Answer Explanation

In the F2 generation of a monohybrid cross, the phenotype that matches the F1 (dominant) appears in 75% (3/4) of the progeny, while the recessive phenotype appears in 25% (1/4). Thus, the order of frequency is 3/4 followed by 1/4.

❓ Why Other Options Are Incorrect

Option B → Incorrectly assigns higher frequency to the recessive trait.

🎯 Strategy

Used: Dimensional/Unit Analysis

Application: Use the 3:1 phenotypic ratio to assign numerical values.

Final Logic: 3/4 > 1/4.

🧠 Memory Trick

3 parts Tall, 1 part Dwarf.

📚 Class XII – Biology – Chapter: Principles of Inheritance and Variation – Topic: Inheritance of One Gene –

10 The lack of "in-between height" in the F1 and F2 generations analytically disproved which common contemporary idea?

A The Law of Segregation.

B The concept of factors as discrete units.

C The theory of blending inheritance.

D The use of Punnett Squares.

💡 Short Explanation

Blending theory suggested intermediates. Mendel observed only distinct parents. This failure to see intermediates falsified blending.

✅ Correct Answer Explanation

"Blending inheritance" was a widespread 19th-century theory suggesting that traits mix (like paint) to create an intermediate phenotype. Mendel's observation that F1 and F2 plants were either "tall" or "dwarf"—with no intermediate heights—provided the crucial evidence to disprove this theory.

❓ Why Other Options Are Incorrect

Option A → This is a law Mendel proposed, not disproved.
Option B → This is a concept he supported.
Option D → Punnett squares are a tool for calculation, not a theory that was disproved.

🎯 Strategy

Used: Elimination

Application: Identify which contemporary theory Mendel's results directly contradicted.

Final Logic: No intermediate phenotype = No blending.

🧠 Memory Trick

Tall or Dwarf = No Blending.

📚 Class XII – Biology – Chapter: Principles of Inheritance and Variation – Topic: Inheritance of One Gene –

11 Analyze the transmission of "factors":
I. They are passed down through gametes.
II. They remain unchanged over successive generations.
III. They contain the specific information required for trait expression.

A I and II are correct.

B II and III are correct.

C I, II, and III are correct.

D None are correct.

💡 Short Explanation

Factors move via gametes (I). They are stable/unchanging (II). They act as information units (III).

✅ Correct Answer Explanation

All three statements describe Mendel's concept of factors. They are the discrete units passed via gametes (sperm/egg) from parents to offspring (I), they remain distinct and do not blend (II), and they function as the blueprints for specific phenotypic traits (III).

❓ Why Other Options Are Incorrect

A, B, and D omit one or more valid properties of Mendelian factors.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Assess each claim against Mendel's particulate theory.

Final Logic: All three attributes define Mendelian factors.

🧠 Memory Trick

Factors = Gametic, Stable, Informative.

📚 Class XII – Biology – Chapter: Principles of Inheritance and Variation – Topic: Inheritance of One Gene –

12 In light of the Chromosomal Theory of Inheritance, which statement is NOT an analytical extension of Mendel's factors?

A Factors (genes) occur in pairs.

B Factors are located on homologous sites on homologous chromosomes.

C Factors segregate independently of chromosomes during meiosis.

D The behavior of chromosomes is parallel to the behavior of genes.

💡 Short Explanation

Factors ARE on chromosomes. Their segregation is tied to chromosome movement. They don't segregate "independently" of them.

✅ Correct Answer Explanation

The Chromosomal Theory of Inheritance states that genes (factors) are located on chromosomes and follow their movement during meiosis. Therefore, factors cannot segregate independently of chromosomes; they segregate because the homologous chromosomes segregate.

❓ Why Other Options Are Incorrect

Option A → Both chromosomes and genes occur in pairs.
Option B → This is a foundational concept of the chromosomal theory.
Option D → This parallelism was the primary evidence for the theory.

🎯 Strategy

Used: Elimination

Application: Use knowledge of the Chromosomal Theory of Inheritance.

Final Logic: If factors are on chromosomes, their movement is linked, not independent.

🧠 Memory Trick

Factors reside on chromosomes.

📚 Class XII – Biology – Chapter: Principles of Inheritance and Variation – Topic: Chromosomal Theory of Inheritance –

📄 Passage

From the observation that the recessive parental trait is expressed without any blending in the F2 generation, we can infer that the alleles segregate during meiosis. This segregation of alleles is a random process and so there is a 50 per cent chance of a gamete containing either allele. During fertilisation, the two alleles from the parents are united to produce zygotes. The 1/4 : 1/2 : 1/4 ratio of TT: Tt: tt is mathematically condensable to the form of the binomial expression (ax +by)^2.

Based on the binomial expansion (1/2T + 1/2t)^2 provided in the passage, what is the frequency of the Tt genotype?

A 1/4.

B 1/2.

C 3/4.

D 1/16.

💡 Short Explanation

Expand: (1/2T + 1/2t)^2. Result: 1/4TT + 2/4Tt + 1/4tt. 2/4 reduces to 1/2.

✅ Correct Answer Explanation

The expansion (1/2T + 1/2t)^2 results in: 1/4TT + 2/4Tt + 1/4tt. The Tt term (2/4Tt) simplifies to 1/2. Thus, the frequency of the Tt genotype is 1/2.

❓ Why Other Options Are Incorrect

Option A → This is the frequency of TT or tt.
Option C → 3/4 is the frequency of the tall phenotype (TT+Tt).
Option D → This is incorrect mathematically.

🎯 Strategy

Used: Dimensional/Unit Analysis

Application: Apply algebraic expansion rules to the binomial expression.

Final Logic: The middle term of a squared binomial (a+b)^2 = a^2 + 2ab + b^2 is 2ab, which here is 2(1/2)(1/2) = 1/2.

🧠 Memory Trick

Binomial expansion mirrors the 1:2:1 ratio.

📚 Class XII – Biology – Chapter: Principles of Inheritance and Variation – Topic: Inheritance of One Gene –

📄 Passage

The passage states allele segregation is a "random process." What is the analytical consequence of this for a heterozygous (Tt) plant?

A All its gametes will carry the T allele.

B It will produce two types of gametes in equal proportion (50% T and 50% t).

C It will only produce tall offspring during self-pollination.

D It will produce gametes that have both T and t together.

💡 Short Explanation

Heterozygote (Tt) gamete formation. Law of Segregation: Factors separate. 50% chance for T, 50% chance for t.

✅ Correct Answer Explanation

Segregation ensures that each gamete receives only one allele from the parent pair. Because T and t are equally likely to be segregated into a gamete, a Tt plant will produce 50% T gametes and 50% t gametes. This randomness ensures that the resulting zygotes reflect the Mendelian ratios.

❓ Why Other Options Are Incorrect

Option A → Segregation results in both alleles, not just T.
Option C → Self-pollination of Tt produces 25% recessive offspring (tt, dwarf).
Option D → Factors segregate away from each other; they do not stay together.

🎯 Strategy

Used: Substitution

Application: Apply the definition of the Law of Segregation to the Tt genotype.

Final Logic: Randomness + Segregation = 1:1 gametic ratio.

🧠 Memory Trick

Segregation = 50-50 split.

📚 Class XII – Biology – Chapter: Principles of Inheritance and Variation – Topic: Law of Segregation –

15 Match the genotypic symbol with its analytical identity:

List-I	List-II
1. Homozygous dominant	a. tt
2. Homozygous recessive	b. Tt
3. Heterozygote	c. TT
4. F₁ Hybrid	d. Tt (result of TT × tt)

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

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

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

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

💡 Short Explanation

TT = Homozygous dominant (1-c). tt = Homozygous recessive (2-a). Tt = Heterozygote (3-b). F1 hybrid = Tt (4-d).

✅ Correct Answer Explanation

The definitions are straightforward: Homozygous dominant (TT), Homozygous recessive (tt), and Heterozygote (Tt). The F1 hybrid resulting from a cross between TT and tt is also the Tt genotype, confirming the matches in option A.

❓ Why Other Options Are Incorrect

All other options incorrectly link the genotypes to the wrong identification terms.

🎯 Strategy

Used: Substitution

Application: Pair each genotype with its standard genetic term.

Final Logic: Standard notation confirms TT=Dom, tt=Rec, Tt=Het.

🧠 Memory Trick

TT = Top (Dominant); tt = Tiny (Recessive).

📚 Class XII – Biology – Chapter: Principles of Inheritance and Variation – Topic: Inheritance of One Gene –

16 Analytically, why does the use of the same letter (T/t) for a character facilitate genetic study?

A It confirms the alleles belong to different genes.

B It allows for the calculation of the 9:3:3:1 ratio.

C It helps remember that T and t are alleles of the same gene/character.

D It is required by the binomial expression (ax+by)^2.

💡 Short Explanation

Same letter = same gene. Case change = different allele. This logic is crucial for tracking trait transmission.

✅ Correct Answer Explanation

Genetic notation uses the same alphabet (e.g., T/t) to show that these versions belong to the same genetic locus (gene). This system is designed specifically to simplify the tracking of allelic variations of a single character, rather than implying the presence of multiple genes.

❓ Why Other Options Are Incorrect

Option A → Using the same letter indicates they are the same gene, not different.
Option B → The ratio depends on segregation, not the specific letter used.
Option D → The math works with any variables (e.g., A/a), not just specific letters.

🎯 Strategy

Used: Elimination

Application: Evaluate which choice explains the pedagogical and analytical purpose of the notation system.

Final Logic: Consistent notation highlights the allelic relationship.

🧠 Memory Trick

Same Letter = Same Locus.

📚 Class XII – Biology – Chapter: Principles of Inheritance and Variation – Topic: Inheritance of One Gene –

17 If Mendel self-pollinated a "tall F2 plant," and it only produced tall plants in the F3 and F4 generations, what would be its likely genotype?

A tt.

B Tt.

C TT.

D It could be TT or Tt.

💡 Short Explanation

Tt would produce some dwarf plants (tt). TT only produces Tall offspring. Stability over generations confirms homozygosity.

✅ Correct Answer Explanation

A Tt (heterozygous) plant would segregate and produce 25% dwarf (tt) offspring upon self-pollination. Since the plant only produced tall plants over multiple generations (F3, F4), it must be homozygous for the dominant allele (TT).

❓ Why Other Options Are Incorrect

Option A → tt is dwarf; it cannot produce tall plants if selfed.
Option B → Tt would produce dwarf offspring.
Option D → Tt cannot be the answer because Tt would yield dwarf offspring.

🎯 Strategy

Used: Substitution

Application: Test the genotypes against the offspring phenotype. Only TT satisfies the "only tall" condition.

Final Logic: Consistent stability across generations implies homozygosity.

🧠 Memory Trick

Stable = Homozygous.

📚 Class XII – Biology – Chapter: Principles of Inheritance and Variation – Topic: Inheritance of One Gene –

18 Which of the following is NOT a possible result of the random union of gametes from a Tt x Tt cross?

A 25% homozygous dominant zygotes.

B 50% heterozygous zygotes.

C 25% homozygous recessive zygotes.

D 50% homozygous tall zygotes.

💡 Short Explanation

Punnett Square (Tt x Tt) gives: 1/4 TT, 1/2 Tt, 1/4 tt. TT is homozygous tall (25%). Option D says 50%, which is wrong.

✅ Correct Answer Explanation

The random union of gametes from Tt x Tt produces: 25% TT (homozygous dominant/tall), 50% Tt (heterozygous), and 25% tt (homozygous recessive). The claim that 50% are "homozygous tall" (TT) is mathematically false; only 25% are TT.

❓ Why Other Options Are Incorrect

Options A, B, and C are the correct expected frequencies in a Tt x Tt cross.

🎯 Strategy

Used: Dimensional/Unit Analysis

Application: Calculate frequencies from the Punnett Square: 1/4 (25%) TT, 1/2 (50%) Tt, 1/4 (25%) tt.

Final Logic: Option D contradicts the established 1/4 : 1/2 : 1/4 ratio.

🧠 Memory Trick

1-2-1 is the ratio, not 2-2-0.

📚 Class XII – Biology – Chapter: Principles of Inheritance and Variation – Topic: Inheritance of One Gene –

19 Arrange the following in order from "Directly Observed" to "Inferred through Testing":
1. Phenotype (e.g., Tallness).
2. Genotype (e.g., Tt or TT).

A 1 then 2

B 2 then 1

C (option not parsed — please edit)

D (option not parsed — please edit)

💡 Short Explanation

Phenotype is the observable appearance. Genotype is the hidden genetic code. We infer the genotype by testing phenotypes.

✅ Correct Answer Explanation

Phenotype (Tall/Dwarf) is directly observable (1). Genotype cannot be seen directly; it is inferred through breeding experiments like test crosses (2). Therefore, the correct order of observation to inference is Phenotype then Genotype.

❓ Why Other Options Are Incorrect

Option B → This reverses the analytical process.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Define the difference between an observable trait (phenotype) and a non-observable code (genotype).

Final Logic: Observable -> Inferred.

🧠 Memory Trick

See (Phenotype) then Search (Genotype).

📚 Class XII – Biology – Chapter: Principles of Inheritance and Variation – Topic: Inheritance of One Gene –

20 What analytical tool did Mendel use to determine the genotype of a tall F2 plant?

A Self-pollination only.

B A test cross with a dwarf plant.

C A monohybrid cross with an F1 plant.

D Analysis of leaf shape.

💡 Short Explanation

F2 Tall could be TT or Tt. Cross with tt (Test cross). If offspring = All Tall, parent was TT. If offspring = 1 Tall : 1 Dwarf, parent was Tt.

✅ Correct Answer Explanation

To distinguish between homozygous dominant (TT) and heterozygous (Tt) genotypes in the F2 generation, Mendel developed the "test cross." By crossing the unknown plant with a homozygous recessive plant (tt), he could look at the offspring: if all were tall, the parent was TT; if there were dwarf individuals, the parent was Tt.

❓ Why Other Options Are Incorrect

Option A → Selfing would take multiple generations to verify; a test cross is direct.
Option C → This does not provide a definitive result for a single F2 plant.
Option D → Leaf shape is irrelevant to the height trait.

🎯 Strategy

Used: Substitution

Application: Define the purpose of a test cross (to reveal unknown genotype).

Final Logic: Test cross = Discovery tool for genotypes.

🧠 Memory Trick

Test Cross = Truth detector.

📚 Class XII – Biology – Chapter: Principles of Inheritance and Variation – Topic: Test Cross –

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