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NEET 2020 Botany Question 8 Solution

Topic: Principles of Inheritance and Variation · Official NTA Booklet Code E1

Question

Select the correct match.

(1)Haemophilia - Y linked
(2)Phenylketonuria - Autosomal dominant trait
(3)Sickle cell anaemia - Autosomal recessive trait, chromosome-11
(4)Thalassemia - X linked

✓

Verified Against NTA Final Answer Key

Option (3) : Sickle cell anaemia - Autosomal recessive trait, chromosome-11

📚 Principles of Inheritance and Variation Easy

📋 Given Parameters & Problem Setup

Listed Disorders Haemophilia, Phenylketonuria, Sickle cell anaemia, Thalassemia

Question Objective Select the correct genetic match regarding inheritance pattern and chromosomal locus

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The 30-Second Exam Hall Shortcut: ⚡ "Sickle Cell = Autosomal Recessive on Chromosome 11 (Beta-Globin Gene)!"

⏱️ Save ~25 seconds

Sickle cell anaemia is caused by a point mutation in the beta-globin gene located on chromosome 11, inherited as an autosomal recessive trait. Haemophilia is X-linked (not Y); PKU is autosomal recessive (not dominant); Thalassemia is autosomal (not X-linked). Pair (3) is 100% correct!

1 Check Haemophilia: X-linked recessive disorder (Queen Victoria pedigree), NOT Y-linked. Pair (1) is False.

2 Check Phenylketonuria (PKU): Autosomal RECESSIVE inborn error of metabolism (PAH gene deficiency), NOT dominant. Pair (2) is False.

3 Check Sickle cell anaemia: Autosomal recessive disorder located on chromosome 11 (HBB gene, codon 6 mutation). Pair (3) is TRUE!

4 Check Thalassemia: Autosomal recessive disorder (alpha on chr-16, beta on chr-11), NOT X-linked. Pair (4) is False.

5 Option (3) is the correct match.

🛡️

Why You Can 100% Trust This Shortcut: NCERT Biology · Principles of Inheritance and Variation (Mendelian Disorders: Sickle-cell anaemia is an autosome-linked recessive trait. The gene for beta-globin is located on chromosome 11. Haemophilia is a sex-linked recessive disease. Phenylketonuria is an autosomal recessive trait. Thalassemia is an autosome-linked recessive blood disease).

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Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Comprehensive Review of Listed Mendelian Disorders

- 1. Haemophilia: A sex-linked (X-linked) recessive blood coagulation disorder involving Factor VIII (Haemophilia A) or Factor IX (Haemophilia B) deficiency. Because it is X-linked, it exhibits criss-cross inheritance and predominantly affects males. It is never Y-linked. - 2. Phenylketonuria (PKU): An autosomal recessive inborn error of phenylalanine metabolism caused by mutation in the gene encoding phenylalanine hydroxylase on chromosome 12. It is not an autosomal dominant trait. - 3. Sickle Cell Anaemia: An autosomal recessive haematological disorder caused by a single nucleotide transversion (GAG $\to$ GUG) at the sixth codon of the $\beta$ -globin gene located on autosomal chromosome 11, replacing glutamic acid with hydrophobic valine. - 4. Thalassemia: An autosomal recessive quantitative hemoglobinopathy caused by defective synthesis of $\alpha$ -globin chains (genes *HBA1* and *HBA2* on autosome chromosome 16) or $\beta$ -globin chains (gene *HBB* on autosome chromosome 11). It is completely autosomal, not sex-linked.

\begin{aligned} \text{Sickle Cell Anaemia} &\iff \mathbf{Autosomal\,Recessive} \quad [\text{Chromosome 11}] \\ \text{Haemophilia} &\iff \mathbf{X\text{-Linked Recessive}} \quad [\text{NOT Y-linked}] \\ \text{Phenylketonuria} &\iff \mathbf{Autosomal\,Recessive} \quad [\text{NOT Dominant}] \\ \text{Thalassemia} &\iff \mathbf{Autosomal\,Recessive} \quad [\text{Chromosomes 16 \& 11}] \end{aligned}

Step 2

Verification of Option (3)

Only pair (3) matches both the mode of inheritance (autosomal recessive) and the chromosomal assignment (chromosome-11) correctly.

⭐

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

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Haemophilia is an X-linked recessive disorder.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing male-predominance with Y-chromosomal inheritance.

2 B

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Phenylketonuria is an autosomal recessive metabolic disorder.

⚠️

Student Fallacy (Why candidates pick this trap): Misting recessive inborn errors of metabolism for dominant traits.

3 C

✓ 100% Correct

Verdict & Scientific Reason:

Correct. Sickle cell anaemia is an autosomal recessive disorder linked to the beta-globin gene on chromosome 11.

💡

Why this is airtight: None. Candidate accurately recalls chromosomal loci of Mendelian disorders.

4 D

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Thalassemia is an autosomal recessive disorder, not X-linked.

⚠️

Student Fallacy (Why candidates pick this trap): Conflating blood disorders (haemophilia and thalassemia) under the X-linked umbrella.

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NTA Trap Alert: Blood Disorder Linkage Conflation Trap

Students frequently group Haemophilia, Sickle Cell, and Thalassemia together as "blood diseases" and confuse their genetic linkage. Haemophilia is X-linked; Sickle cell and Thalassemia are strictly autosomal.

🛡️ How to avoid the -1 mark: Remember: Haemophilia = X-linked. Sickle Cell & Thalassemia = Autosomal.

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Core NEET Syllabus Standard

NEET / NCERT Biology · Principles of Inheritance and Variation Standard Benchmark

Core Scientific Principle Tested:

"Sickle cell anaemia is an autosome-linked recessive trait controlled by a gene on chromosome 11."

Syllabus Focus: Mendelian Disorders

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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NEET 2020 Botany Question 8 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ "Sickle Cell = Autosomal Recessive on Chromosome 11 (Beta-Globin Gene)!"

Step-by-Step Rigorous Workflow & Mathematical Proof

Comprehensive Review of Listed Mendelian Disorders

Verification of Option (3)

360° Option Elimination Engine Key Feature

NTA Trap Alert: Blood Disorder Linkage Conflation Trap

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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