MyCompetitiveExams Logo MyCompetitiveExams
MyCompetitiveExams Logo MyCompetitiveExams
Search 1,140+ Questions
Chapters, formulas, speed tricks
→
⚡ Brahmastra NEET 2027
720 MARKS

Dynamic 180-question full-length simulator mixed dynamically from all 6 years for 2027 & 2026 aspirants.

Launch Brahmastra 2027 Test →
Start Practice →
100% Free · No Login Required
Q.104 Botany ⭐ 360° Option Elimination Active
Vault ↗

NEET 2021 Botany Question 104 Solution

Topic: Cell: The Unit of Life · Official NTA Booklet Code M1
NEET 2021 Botany Question 104: Classification of Chromosomes Based on Centromere Position

Question

When the centromere is situated in the middle of two equal arms of chromosomes, the chromosome is referred as:

  1. (1)Metacentric
  2. (2)Telocentric
  3. (3)Sub-metacentric
  4. (4)Acrocentric
✓
Verified Against NTA Final Answer Key
Option (1) : Metacentric
📚 Cell: The Unit of Life Easy
📋 Given Parameters & Problem Setup
Centromere Position Middle of two equal arms
Resulting Morphology Chromosome with two equal arms (V-shaped during anaphase)
⚡

The 30-Second Exam Hall Shortcut: ⚡ Centromere in the Middle = "Meta"centric (V-shaped)

⏱️ Save ~20 seconds

A chromosome having its centromere located exactly at the center between two equal-length arms is a metacentric chromosome (forming a V shape at anaphase). Sub-metacentric = unequal arms (L); Acrocentric = near end (J); Telocentric = terminal (I). Match Option (1)!

1 Metacentric: Centromere in middle   ⟹  \implies two equal arms (p=qp = q, V-shape).
2 Sub-metacentric: Centromere slightly away from middle   ⟹  \implies one shorter (pp) and one longer (qq) arm (L-shape).
3 Acrocentric: Centromere close to end   ⟹  \implies extremely short and very long arm (J-shape).
4 Telocentric: Centromere at terminal tip   ⟹  \implies single arm appearance (I-shape).
5 Match Option (1).
🛡️
Why You Can 100% Trust This Shortcut: Canonical NCERT Cell Biology taxonomy on Chromosome Types.
📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Morphological Classification of Chromosomes

Based on the relative position of the primary constriction (centromere), eukaryotic chromosomes are classified into four distinct types:

Metacentric:Centromere at median position   ⟹  Two equal arms (p=q)Sub-metacentric:Centromere sub-median   ⟹  One shorter (p) and one longer (q) armAcrocentric:Centromere sub-terminal   ⟹  One extremely short and one very long armTelocentric:Centromere terminal   ⟹  Centromere at the very tip\begin{aligned} \text{\textbf{Metacentric:}} & \quad \text{Centromere at median position } \implies \text{Two equal arms } (p = q) \\[4pt] \text{\textbf{Sub-metacentric:}} & \quad \text{Centromere sub-median } \implies \text{One shorter } (p) \text{ and one longer } (q) \text{ arm} \\[4pt] \text{\textbf{Acrocentric:}} & \quad \text{Centromere sub-terminal } \implies \text{One extremely short and one very long arm} \\[4pt] \text{\textbf{Telocentric:}} & \quad \text{Centromere terminal } \implies \text{Centromere at the very tip} \end{aligned}
Step 2

Anaphase Configuration Diagnostic

During anaphase separation, centromeric spindle attachment creates distinctive shapes: - Metacentric: V-shaped. - Sub-metacentric: L-shaped. - Acrocentric: J-shaped. - Telocentric: I-shaped. Since the question specifies two equal arms with a central centromere, it corresponds unequivocally to metacentric.

⭐

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
✓ 100% Correct
Verdict & Scientific Reason:

Metacentric chromosome has the centromere precisely in the middle forming two equal arms.

💡
Why this is airtight: None. Textbook definition.
2 2
✗ Incorrect
Verdict & Scientific Reason:

Telocentric chromosome has a terminal centromere situated at the very end of the chromosome arm.

⚠️
Student Fallacy (Why candidates pick this trap): Confusing terminal (telomeric) position with central (median) position.
3 3
✗ Incorrect
Verdict & Scientific Reason:

Sub-metacentric chromosome has the centromere located slightly away from the center, producing unequal arms.

⚠️
Student Fallacy (Why candidates pick this trap): Assuming sub-metacentric means "nearly equal" arms.
4 4
✗ Incorrect
Verdict & Scientific Reason:

Acrocentric chromosome has the centromere close to one end, giving one extremely short and one very long arm.

⚠️
Student Fallacy (Why candidates pick this trap): Overlooking the "equal arms" stipulation in the problem statement.
⚠️

NTA Trap Alert: Metacentric vs Sub-metacentric Arm Length Criterion

NTA specifies "two equal arms". Any displacement from the middle makes the arms unequal (short arm p and long arm q), converting it to sub-metacentric.

🛡️ How to avoid the -1 mark: Equal arms = Metacentric (Middle = Meta).
📖

Core NEET Syllabus Standard

NEET / NCERT Biology · Cell: The Unit of Life Standard Benchmark
Core Scientific Principle Tested:

"A metacentric chromosome has a middle centromere forming two equal arms of the chromosome."

Syllabus Focus: Nucleus and Chromosome Morphology
✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

Ready to attempt under real exam pressure?

Test your speed and accuracy in the authentic 200-minute timed NTA simulator.

Launch NEET 2021 CBT Test →

Spotted a mistake in this solution? Report an error (support@mycompetitiveexams.com)

⚖️ Legal & Fair Dealing Notice: Sourced from publicly released NEET 2021 question papers and NEET answer keys for private study, research, and non-commercial educational practice under Fair Dealing (Section 52(1)(a) of the Indian Copyright Act, 1957). Not affiliated with or endorsed by NTA or NMC.

Solve 4 NEET Questions a Day — One per Subject

Cover all 1,140 official NEET questions in 285 days at your own pace. Progress is saved on your device. No login needed.