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NEET 2023 Botany Question 120 Solution

Topic: Principles of Inheritance and Variation · Official NTA Booklet Code G5

Question

The phenomenon of pleiotropism refers to

(1)more than two genes affecting a single character.
(2)presence of several alleles of a single gene controlling a single crossover.
(3)presence of two alleles, each of the two genes controlling a single trait.
(4)a single gene affecting multiple phenotypic expression.

✓

Verified Against NTA Final Answer Key

Option (4) : a single gene affecting multiple phenotypic expression.

📚 Principles of Inheritance and Variation Easy

📋 Given Parameters & Problem Setup

Genetic Phenomenon Pleiotropism / Pleiotropy

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The 30-Second Exam Hall Shortcut: ⚡ Pleiotropy vs. Polygenic Inheritance Anchor

⏱️ Save ~20 seconds

Contrast the opposites: Polygenic = Many genes control 1 phenotype (e.g., human skin color). Pleiotropy = 1 single gene controls multiple phenotypes (e.g., phenylketonuria, starch grain size & seed shape in pea)!

1 Multiple alleles: More than two alleles governing a single character (e.g., ABO blood group).

2 Polygenic inheritance: Several genes collectively affecting a single continuous character.

3 Pleiotropy: A single gene product affecting multiple distinct phenotypic traits simultaneously.

4 Match Option (4) a single gene affecting multiple phenotypic expression.

🛡️

Why You Can 100% Trust This Shortcut: Canonical NCERT Genetics definitions of non-Mendelian inheritance patterns.

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Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Definition of Pleiotropy

Pleiotropy is the phenomenon wherein a single gene influences multiple unrelated phenotypic traits:

\text{\textbf{Pleiotropic Gene}} \longrightarrow \begin{cases} \text{Phenotypic Trait } 1 \\[2pt] \text{Phenotypic Trait } 2 \\[2pt] \text{Phenotypic Trait } 3 \end{cases}

Step 2

Biochemical Basis and Canonical Examples

The underlying mechanism in most cases is the effect of the gene product on a central metabolic pathway that contributes to different development systems:

\begin{aligned} \text{\textbf{Phenylketonuria (PKU):}} & \quad \text{Mutation in PAH gene } \longrightarrow \begin{cases} \text{Mental retardation} \\[2pt] \text{Reduction in hair} \\[2pt] \text{Skin pigmentation changes} \end{cases} \\[4pt] \text{\textbf{Pea Starch Branching (B/b):}} & \quad \text{Controls both starch synthesis (size) AND seed shape (round/wrinkled)} \end{aligned}

Step 3

Verbatim NCERT Definition

NCERT defines pleiotropy: "There are instances where a single gene can exhibit multiple phenotypic expressions. Such a gene is called a pleiotropic gene."

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4-Option Deep Scan

1 1

✗ Incorrect

Verdict & Scientific Reason:

This describes polygenic inheritance (quantitative inheritance), not pleiotropy.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing polygenic inheritance with pleiotropy.

2 2

✗ Incorrect

Verdict & Scientific Reason:

Nonsensical biological statement; multiple alleles govern traits, not crossover events.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing multiple allelism with pleiotropy.

3 3

✗ Incorrect

Verdict & Scientific Reason:

Describes standard dihybrid or two-gene interaction (epistasis/complementary genes).

⚠️

Student Fallacy (Why candidates pick this trap): Confusing intergenic interactions with pleiotropy.

4 4

✓ 100% Correct

Verdict & Scientific Reason:

Accurate and verbatim NCERT definition of pleiotropism.

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Why this is airtight: None; textbook verbatim.

⚠️

NTA Trap Alert: Pleiotropy vs. Polygenic Inverse Trap

Pleiotropy and polygenic inheritance are exact inverses: Polygenic = Many genes → One trait; Pleiotropy = One gene → Many traits.

🛡️ How to avoid the -1 mark: Remember: "Plei-" means more (effects) from one gene. "Poly-" means many genes for one effect.

📖

Core NEET Syllabus Standard

NCERT Biology · Principles of Inheritance and Variation Standard Benchmark

Core Scientific Principle Tested:

"A single gene can exhibit multiple phenotypic expressions. Such a gene is called a pleiotropic gene."

Syllabus Focus: Pleiotropy

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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NEET 2023 Botany Question 120 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Pleiotropy vs. Polygenic Inheritance Anchor

Step-by-Step Rigorous Workflow & Mathematical Proof

Definition of Pleiotropy

Biochemical Basis and Canonical Examples

Verbatim NCERT Definition

360° Option Elimination Engine Key Feature

NTA Trap Alert: Pleiotropy vs. Polygenic Inverse Trap

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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