Q.169 Zoology ⭐ 360° Option Elimination Active

NEET 2023 Zoology Question 169 Solution

Topic: Molecular Basis of Inheritance · Official NTA Booklet Code G5

Question

Match List I with List II. List I: A. Gene 'a'; B. Gene 'y'; C. Gene 'i'; D. Gene 'z'. List II: I. β-galactosidase; II. Transacetylase; III. Permease; IV. Repressor protein. Choose the correct answer from the options given below:

✓

Verified Against NTA Final Answer Key

Option (3) : A-II, B-III, C-IV, D-I

📚 Molecular Basis of Inheritance Easy

📋 Given Parameters & Problem Setup

Operon System Lac Operon (Lactose Operon in E. coli)

Genes Gene a, Gene y, Gene i, Gene z

⚡

The 30-Second Exam Hall Shortcut: ⚡ Lac Operon "Z-Y-A" + "i" Code

⏱️ Save ~20 seconds

Remember the order: Gene i = Repressor protein (IV). Gene z = β-galactosidase (I). Gene y = Permease (III). Gene a = Transacetylase (II). Match Option (3)!

1 Gene i (inhibitor): Codes for the lac repressor protein -> C-IV.

2 Gene z: Codes for beta-galactosidase (hydrolyzes lactose) -> D-I.

3 Gene y: Codes for permease (increases cell permeability to beta-galactosides) -> B-III.

4 Gene a: Codes for transacetylase -> A-II.

5 Match combination: A-II, B-III, C-IV, D-I -> Option (3).

🛡️

Why You Can 100% Trust This Shortcut: Canonical NCERT Molecular Genetics Jacob-Monod lac operon structural gene inventory.

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Organization of the Lac Operon Genes

The lactose operon of $\textit{E. coli}$ consists of one regulatory gene and three polycistronic structural genes:

\begin{aligned} \text{\textbf{Gene } } \mathbf{i}\textbf{ (Inhibitor):} & \quad \text{Synthesizes the active } \mathbf{\text{Repressor protein}} \implies \mathbf{\text{IV}} \\[4pt] \text{\textbf{Gene } } \mathbf{z}\textbf{:} & \quad \text{Codes for } \mathbf{\beta\text{\textbf{-galactosidase}}} \text{ (hydrolyzes lactose to glucose + galactose)} \implies \mathbf{\text{I}} \\[4pt] \text{\textbf{Gene } } \mathbf{y}\textbf{:} & \quad \text{Codes for } \mathbf{\text{Permease}} \text{ (facilitates lactose entry)} \implies \mathbf{\text{III}} \\[4pt] \text{\textbf{Gene } } \mathbf{a}\textbf{:} & \quad \text{Codes for } \mathbf{\text{Transacetylase}} \implies \mathbf{\text{II}} \end{aligned}

Step 2

Verbatim NCERT Reference

NCERT states verbatim: "The z gene codes for beta-galactosidase... The y gene codes for permease... The a gene encodes a transacetylase... The i gene codes for the repressor of the lac operon."

Step 3

Option Elimination

Matching C-IV and D-I immediately narrows to Option (3), completely ruling out Options 1, 2, and 4.

⭐

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 1

✗ Incorrect

Verdict & Scientific Reason:

Mismatches Gene a with permease and Gene z with transacetylase.

⚠️

Student Fallacy (Why candidates pick this trap): Scrambling structural gene enzymatic products.

2 2

✗ Incorrect

Verdict & Scientific Reason:

Mismatches Gene y with β-galactosidase and Gene z with permease.

⚠️

Student Fallacy (Why candidates pick this trap): Inverting gene z and gene y products.

3 3

✓ 100% Correct

Verdict & Scientific Reason:

Exact match with the canonical NCERT gene-product associations for the lac operon.

💡

Why this is airtight: None; textbook verbatim match.

4 4

✗ Incorrect

Verdict & Scientific Reason:

Mismatches Gene i with β-galactosidase.

⚠️

Student Fallacy (Why candidates pick this trap): Mistaking the "i" gene for an inducer rather than the repressor inhibitor.

⚠️

NTA Trap Alert: Gene "i" = Inhibitor (Repressor), NOT Inducer!

Students frequently think the letter "i" in gene i stands for "inducer". The inducer is lactose/allolactose. The letter "i" stands for "inhibitor", which produces the repressor protein.

🛡️ How to avoid the -1 mark: Remember: Gene i = Inhibitor (codes for Repressor). Inducer = Allolactose (metabolite, not a gene).

📖

Core NEET Syllabus Standard

NCERT Biology · Molecular Basis of Inheritance Standard Benchmark

Core Scientific Principle Tested:

"In lac operon, z gene codes for beta-galactosidase, y gene codes for permease, a gene codes for transacetylase, and i gene codes for repressor."

Syllabus Focus: The Lac Operon

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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NEET 2023 Zoology Question 169 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Lac Operon "Z-Y-A" + "i" Code

Step-by-Step Rigorous Workflow & Mathematical Proof

Organization of the Lac Operon Genes

Verbatim NCERT Reference

Option Elimination

360° Option Elimination Engine Key Feature

NTA Trap Alert: Gene "i" = Inhibitor (Repressor), NOT Inducer!

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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