Q.175 Zoology ⭐ 360° Option Elimination Active

NEET 2026 Zoology Question 175 Solution

Topic: Principles of Inheritance and Variation · Official NTA Booklet Code 50

Question

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R. Assertion A: In an experiment, Mendel observed that the F₁ progeny plants are all tall and none are dwarf. Reason R: Stem height is a contrasting trait, with tall being dominant and dwarf being recessive. In the light of the above statements, choose the most appropriate answer from the options given below:

✓

Verified Against NTA Final Answer Key

Option (1) : Both (A) and (R) are true and (R) is the correct explanation of (A)

📚 Principles of Inheritance and Variation Easy

📋 Given Parameters & Problem Setup

Cross True-breeding Tall (TT) × True-breeding Dwarf (tt)

Assertion (A) In a monohybrid cross between true-breeding tall and true-breeding dwarf pea plants, all F₁ progeny were tall.

Reason (R) The allele for tallness is dominant over the allele for dwarfness, expressing itself in heterozygous condition (Tt).

⚡

The 30-Second Exam Hall Shortcut: ⚡ Law of Dominance "Because" Check

⏱️ Save ~35 seconds

All F₁ are tall BECAUSE tall (T) dominates over dwarf (t) in heterozygotes!

1 Read Assertion (A): In cross TT × tt, all F₁ offspring are phenotypically tall -> TRUE (NCERT monohybrid cross).

2 Read Reason (R): Allele for tallness (T) is dominant over allele for dwarfness (t), expressing in heterozygous Tt -> TRUE (Mendel’s Law of Dominance).

3 Apply "BECAUSE": All F₁ progeny are tall BECAUSE the dominant tall allele masks the recessive dwarf allele in the heterozygous Tt genotype.

4 Reason (R) gives the exact genetic explanation for Assertion (A).

5 Pick Option (1) in under 15 seconds!

🛡️

Why You Can 100% Trust This Shortcut: NCERT Biology · Principles of Inheritance and Variation (Incomplete Dominance: Snapdragon Antirrhinum 1:2:1 red, pink, white ratio).

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Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Mendel’s Monohybrid Cross (F₁ Generation)

When Mendel crossed true-breeding tall pea plants (TT) with true-breeding dwarf pea plants (tt), each parent produced only one type of gamete: T and t respectively. Fusion of these gametes produced F₁ progeny with uniform heterozygous genotype Tt, all exhibiting the tall phenotype.

P_1 (TT) \times P_2 (tt) \implies \text{Gametes: } T \times t \implies F_1: Tt \quad (\text{100\% Tall})

• Assertion (A) is completely true.

Step 2

Law of Dominance as the Mechanism

According to Mendel’s Law of Dominance: (i) Characters are controlled by discrete units called factors (genes). (ii) Factors occur in pairs. (iii) In a dissimilar pair of factors, one member of the pair dominates (dominant) the other (recessive). Because T completely dominates t in Tt, the dwarf trait is masked in F₁, perfectly explaining Assertion (A).

T \text{ (Dominant)} > t \text{ (Recessive)} \implies Tt \text{ Phenotype} = \text{Tall} \implies (R) \text{ explains } (A)

• Recessive dwarf phenotype reappears only in F₂ in homozygous condition (tt).

⭐

360° Option Elimination Engine Key Feature

Diagnose every choice: Know exactly why the right option works and why distractors fail.

4-Option Deep Scan

1 A

✓ 100% Correct

Verdict & Scientific Reason:

100% correct. Dominance of the tall allele over the dwarf allele is the precise scientific explanation for the 100% tall F₁ generation.

💡

Why this is airtight: None; textbook Mendelian genetics.

2 B

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. (R) is the exact biological cause of the phenotype described in (A).

⚠️

Student Fallacy (Why candidates pick this trap): Failing to recognize the causal relationship.

3 C

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Reason (R) is the universally accepted definition of complete dominance.

⚠️

Student Fallacy (Why candidates pick this trap): Doubting the dominance of the tall allele.

4 D

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Assertion (A) is a historic empirical result.

⚠️

Student Fallacy (Why candidates pick this trap): Thinking dwarf plants appeared in F₁.

⚠️

NTA Trap Alert: F₁ vs. F₂ Generation Confusion

Do not confuse F₁ with F₂. In F₁, ALL plants are tall (100% tall, 0% dwarf). The 3:1 phenotypic ratio only appears in the F₂ generation after selfing F₁ plants.

🛡️ How to avoid the -1 mark: Double check whether the statement refers to F₁ or F₂.

📖

Core NEET Syllabus Standard

NEET Biology Core Syllabus · Principles of Inheritance and Variation Standard Benchmark

Core Scientific Principle Tested:

"In a monohybrid cross, only the dominant trait is expressed in the F₁ generation due to masking of the recessive allele."

Syllabus Focus: Law of Dominance

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

Dominant T hides recessive t: F₁ is 100% Tall!

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NEET 2026 Zoology Question 175 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Law of Dominance "Because" Check

Step-by-Step Rigorous Workflow & Mathematical Proof

Mendel’s Monohybrid Cross (F₁ Generation)

Law of Dominance as the Mechanism

360° Option Elimination Engine Key Feature

NTA Trap Alert: F₁ vs. F₂ Generation Confusion

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

🔗 Related Questions — Principles of Inheritance and Variation

Polygenic Inheritance Pattern (Quantitative Inheritance)

Mendelian Dihybrid Cross and F2 Phenotypic Ratio (9:3:3:1)

Pedigree Probability Calculation for X-Linked Recessive Carrier Offspring

Postulates of Mendel's Law of Dominance

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