Q.172 Zoology ⭐ 360° Option Elimination Active

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NEET 2023 Zoology Question 172 Solution

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

Question

Broad palm with single palm crease is visible in a person suffering from-

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Verified Against NTA Final Answer Key

Option (2) : Down’s syndrome

📚 Principles of Inheritance and Variation Easy

📋 Given Parameters & Problem Setup

Phenotypic Marker Broad palm with single palm crease (Simian crease)

Etiology Chromosomal aneuploidy (Trisomy 21)

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The 30-Second Exam Hall Shortcut: ⚡ Broad Palm with Single Crease = Down's Syndrome

⏱️ Save ~20 seconds

Verbatim NCERT clinical description of Down's syndrome (Trisomy 21): "The affected individual is short statured with small round head, furrowed tongue and partially open mouth. Palm is broad with characteristic palm crease!" Instant 5-second recall!

1 Thalassemia: Mendelian microcytic hypochromic hemolytic anemia.

2 Turner's syndrome (45, X0): Sterile female with webbed neck and rudimentary ovaries.

3 Klinefelter's syndrome (47, XXY): Sterile male with gynaecomastia.

4 Down's syndrome (Trisomy 21): Broad palm with single horizontal palmar crease (Simian crease).

5 Match Option (2) Down's syndrome.

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Why You Can 100% Trust This Shortcut: Canonical NCERT Genetics Down's syndrome morphological hallmarks.

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Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Cytogenetics of Down's Syndrome

First described by Langdon Down in 1866, Down's syndrome is an autosomal aneuploidy caused by nondisjunction resulting in trisomy of chromosome 21 ( $2n + 1 = 47$ ):

\text{Karyotype: } 45\text{ Autosomes} + \text{XX / XY} = \mathbf{47\text{ Chromosomes (Trisomy 21)}}

Step 2

Verbatim NCERT Phenotypic Features

NCERT provides four unmistakable physical signs: 1. Short statured with small round head. 2. Furrowed tongue and partially open mouth. 3. Palm is broad with characteristic palm crease (Simian crease). 4. Physical, psychomotor, and mental development is retarded.

Step 3

Elimination of Other Genetic Disorders

Thalassemia affects globin chain synthesis. Turner's syndrome ( $45, XO$ ) presents with short stature and webbed neck. Klinefelter's ( $47, XXY$ ) presents with tall stature and gynaecomastia.

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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:

Thalassemia is an autosomal recessive hemoglobinopathy causing severe hemolytic anemia, without palm crease anomalies.

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Student Fallacy (Why candidates pick this trap): Confusing single-gene blood disorders with chromosomal syndromes.

2 2

✓ 100% Correct

Verdict & Scientific Reason:

Verbatim NCERT diagnostic symptom: broad palm with single transverse palmar crease characterizes Down's syndrome.

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Why this is airtight: None; textbook verbatim recall.

3 3

✗ Incorrect

Verdict & Scientific Reason:

Turner's syndrome is characterized by sterile female phenotype, webbed neck, and shield chest, not broad palm crease.

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Student Fallacy (Why candidates pick this trap): Confusing Turner's short stature with Down's palmar signs.

4 4

✗ Incorrect

Verdict & Scientific Reason:

Klinefelter's syndrome is characterized by tall stature, feminine fat distribution, and gynaecomastia.

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Student Fallacy (Why candidates pick this trap): Confusing aneuploidy phenotypes.

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NTA Trap Alert: Palm Crease vs. Webbed Neck Distinction Trap

Students frequently mix up the physical hallmarks of Down's syndrome (broad palm with single crease, furrowed tongue) with Turner's syndrome (webbed neck, rudimentary ovaries).

🛡️ How to avoid the -1 mark: Broad palm with single crease = Down's syndrome. Webbed neck = Turner's syndrome.

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Core NEET Syllabus Standard

NCERT Biology · Principles of Inheritance and Variation Standard Benchmark

Core Scientific Principle Tested:

"In Down's syndrome, the palm is broad with characteristic palm crease, along with a furrowed tongue and partially open mouth."

Syllabus Focus: Chromosomal Disorders (Down's Syndrome)

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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NEET 2023 Zoology Question 172 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Broad Palm with Single Crease = Down's Syndrome

Step-by-Step Rigorous Workflow & Mathematical Proof

Cytogenetics of Down's Syndrome

Verbatim NCERT Phenotypic Features

Elimination of Other Genetic Disorders

360° Option Elimination Engine Key Feature

NTA Trap Alert: Palm Crease vs. Webbed Neck Distinction Trap

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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