Chapter 6: Molecular Basis of Inheritance – MCQs with Answers & Explanations

CBSE Class 12 Biology MCQs with Answers & Explanations (NCERT): Molecular Basis of Inheritance

Course & Examination Details

• Course: CBSE Class 12 Biology
• Unit: Unit II – Genetics and Evolution
• Chapter: Chapter 6 – Molecular Basis of Inheritance
• Prescribed Textbook: NCERT Biology Class XII
• Examination: CBSE Class 12 Board Examination
• Question Type: Multiple Choice Questions (MCQs)
• Coverage: Conceptual, application-based, competency-oriented

Section A: DNA as Genetic Material

Q1. Which property is essential for a molecule to act as genetic material?

A. High solubility
B. Ability to replicate
C. High molecular weight
D. Large size

Correct Answer: B
Explanation: Genetic material must replicate accurately to ensure continuity of hereditary information across generations.

Q2. DNA is considered a better genetic material than RNA because DNA:

A. Is single stranded
B. Contains uracil
C. Is chemically more stable
D. Mutates rapidly

Correct Answer: C
Explanation: DNA lacks the reactive 2′-OH group and is double stranded, making it more stable than RNA.

Q3. Which experiment finally confirmed DNA as the genetic material?

A. Griffith’s experiment
B. Avery–MacLeod–McCarty experiment
C. Meselson–Stahl experiment
D. Hershey–Chase experiment

Correct Answer: D
Explanation: The Hershey–Chase experiment conclusively showed that DNA, not protein, enters the host cell and carries genetic information.

Q4. RNA acts as genetic material in:

A. Bacteria
B. Plants
C. Animals
D. Some viruses

Correct Answer: D
Explanation: Certain viruses like TMV use RNA as genetic material due to absence of DNA.

Q5. The transforming principle identified by Avery and coworkers was:

A. Protein
B. RNA
C. DNA
D. Lipid

Correct Answer: C
Explanation: Destruction of DNA alone prevented transformation, proving DNA is the genetic material.

Section B: Structure of DNA and RNA

Q6. The double helical structure of DNA was proposed by:

A. Meselson and Stahl
B. Hershey and Chase
C. James Watson and Francis Crick
D. Griffith and Avery

Correct Answer: C
Explanation: Watson and Crick proposed the double helix model based on X-ray diffraction data and Chargaff’s rules.

Q7. Which base pairing is correct in DNA?

A. A–G
B. T–C
C. A–T
D. G–T

Correct Answer: C
Explanation: Adenine pairs with thymine via two hydrogen bonds.

Q8. The sugar present in RNA is:

A. Deoxyribose
B. Ribose
C. Glucose
D. Fructose

Correct Answer: B
Explanation: RNA contains ribose sugar, which has a hydroxyl group at the 2′ carbon.

Q9. Which bond links nucleotides in a DNA strand?

A. Hydrogen bond
B. Glycosidic bond
C. Phosphodiester bond
D. Peptide bond

Correct Answer: C
Explanation: Phosphodiester bonds link adjacent nucleotides in the sugar-phosphate backbone.

Q10. Antiparallel orientation of DNA strands means:

A. Both strands run 5′→3′
B. Both strands run 3′→5′
C. One strand runs 5′→3′, other 3′→5′
D. Strands are circular

Correct Answer: C
Explanation: Antiparallel arrangement is essential for complementary base pairing and replication.

Section C: Replication of DNA

Q11. DNA replication is described as semi-conservative because:

A. Entire DNA is conserved
B. Only one strand is copied
C. Each daughter DNA has one old and one new strand
D. Replication occurs partially

Correct Answer: C
Explanation: Each new DNA molecule contains one parental strand and one newly synthesized strand.

Q12. The enzyme responsible for unwinding DNA during replication is:

A. DNA polymerase
B. RNA polymerase
C. Helicase
D. Ligase

Correct Answer: C
Explanation: Helicase breaks hydrogen bonds to separate DNA strands.

Q13. Okazaki fragments are formed on:

A. Leading strand
B. Lagging strand
C. Template strand
D. Coding strand

Correct Answer: B
Explanation: Lagging strand synthesis is discontinuous due to opposite orientation.

Q14. Which enzyme joins Okazaki fragments?

A. Helicase
B. Primase
C. DNA polymerase
D. DNA ligase

Correct Answer: D
Explanation: DNA ligase forms phosphodiester bonds between fragments.

Q15. DNA polymerase synthesises DNA in which direction?

A. 3′→5′
B. 5′→3′
C. Both directions
D. Randomly

Correct Answer: B
Explanation: DNA polymerase adds nucleotides only at the 3′ end.

Section D: Transcription

Q16. Transcription is the synthesis of:

A. DNA from RNA
B. RNA from DNA
C. Protein from DNA
D. Protein from RNA

Correct Answer: B
Explanation: RNA is synthesized using DNA as a template.

Q17. Which enzyme carries out transcription?

A. DNA polymerase
B. RNA polymerase
C. Ligase
D. Helicase

Correct Answer: B
Explanation: RNA polymerase catalyses RNA synthesis.

Q18. Transcription is asymmetric because:

A. Both DNA strands are transcribed
B. Only one strand acts as template
C. RNA is double stranded
D. RNA polymerase is absent

Correct Answer: B
Explanation: Only the template strand is transcribed to avoid formation of double-stranded RNA.

Q19. In RNA, thymine is replaced by:

A. Adenine
B. Guanine
C. Cytosine
D. Uracil

Correct Answer: D
Explanation: Uracil pairs with adenine in RNA.

Q20. Which RNA carries genetic information to ribosomes?

A. tRNA
B. rRNA
C. mRNA
D. snRNA

Correct Answer: C
Explanation: mRNA carries codons for protein synthesis.

Section E: Genetic Code

Q21. Genetic code is a:

A. Doublet code
B. Triplet code
C. Quadruplet code
D. Single code

Correct Answer: B
Explanation: Three nucleotides form one codon.

Q22. Which codon acts as start codon?

A. UAA
B. UGA
C. AUG
D. UAG

Correct Answer: C
Explanation: AUG codes for methionine and initiates translation.

Q23. The genetic code is degenerate because:

A. One codon codes many amino acids
B. One amino acid has many codons
C. Codons overlap
D. Codons are ambiguous

Correct Answer: B
Explanation: Multiple codons can specify the same amino acid.

Q24. Stop codons do not code for any amino acid because they:

A. Start transcription
B. Terminate translation
C. Code for enzymes
D. Are absent in mRNA

Correct Answer: B
Explanation: Stop codons signal the end of polypeptide synthesis.

Q25. Genetic code is said to be universal because:

A. It differs in organisms
B. It is same in all cells
C. Same codon codes same amino acid in most organisms
D. It codes all proteins

Correct Answer: C
Explanation: Universality indicates common evolutionary origin.

Section F: Translation

Q26. Translation occurs at:

A. Nucleus
B. Mitochondria
C. Ribosomes
D. Lysosomes

Correct Answer: C
Explanation: Ribosomes are sites of protein synthesis.

Q27. tRNA is called adaptor molecule because it:

A. Stores genetic information
B. Transfers amino acids
C. Adapts codons to amino acids
D. Forms ribosomes

Correct Answer: C
Explanation: tRNA links codons with specific amino acids.

Q28. Anticodon is present on:

A. mRNA
B. rRNA
C. tRNA
D. DNA

Correct Answer: C
Explanation: Anticodon pairs with codon during translation.

Q29. Peptide bond formation is catalysed by:

A. Protein enzyme
B. DNA
C. rRNA
D. mRNA

Correct Answer: C
Explanation: rRNA has catalytic activity in ribosomes.

Q30. Energy for translation is provided by:

A. ATP only
B. GTP only
C. ATP and GTP
D. NADH

Correct Answer: C
Explanation: Both ATP and GTP are required during translation.

Section G: Regulation of Gene Expression

Q31. Gene regulation is necessary to:

A. Increase mutations
B. Prevent DNA replication
C. Control protein synthesis
D. Destroy mRNA

Correct Answer: C
Explanation: Regulation ensures proteins are produced only when needed.

Q32. An operon consists of:

A. Only structural genes
B. Structural genes, promoter, operator
C. Only regulator gene
D. Only promoter

Correct Answer: B
Explanation: These components function together in gene regulation.

Q33. Lac operon is an example of:

A. Repressible operon
B. Inducible operon
C. Constitutive operon
D. Mutant operon

Correct Answer: B
Explanation: It is induced in presence of lactose.

Q34. In absence of lactose, lac operon is:

A. Fully active
B. Partially active
C. Switched off
D. Mutated

Correct Answer: C
Explanation: Repressor binds operator, blocking transcription.

Q35. Regulator gene produces:

A. Enzymes
B. RNA polymerase
C. Repressor protein
D. Structural proteins

Correct Answer: C
Explanation: Repressor controls transcription of structural genes.

Section H: Human Genome Project

Q36. The Human Genome Project aimed to:

A. Clone humans
B. Identify all human genes
C. Modify DNA
D. Destroy diseases

Correct Answer: B
Explanation: HGP focused on sequencing and mapping the human genome.

Q37. Approximate number of genes in humans is:

A. 3,000
B. 10,000
C. 30,000
D. 1,00,000

Correct Answer: C
Explanation: HGP revealed humans have about 30,000 genes.

Q38. Percentage of human DNA identical among individuals is:

A. 90%
B. 95%
C. 99%
D. 99.9%

Correct Answer: D
Explanation: Only 0.1% variation exists among humans.

Q39. Bioinformatics deals with:

A. DNA replication
B. Protein synthesis
C. Data analysis using computers
D. Gene mutation

Correct Answer: C
Explanation: Bioinformatics stores and analyses biological data computationally.

Q40. Which DNA region does not code for proteins?

A. Exons
B. Introns
C. Structural genes
D. Promoter

Correct Answer: B
Explanation: Introns are non-coding sequences.

Section I: DNA Fingerprinting

Q41. DNA fingerprinting is based on:

A. Gene mutation
B. Base composition
C. Polymorphism in repetitive DNA
D. Coding DNA

Correct Answer: C
Explanation: Variations in VNTRs create unique patterns.

Q42. DNA fingerprinting was developed by:

A. Watson
B. Crick
C. Alec Jeffreys
D. Meselson

Correct Answer: C
Explanation: Alec Jeffreys developed DNA fingerprinting technique.

Q43. VNTR stands for:

A. Variable Nucleotide Tandem Repeat
B. Variable Number Tandem Repeat
C. Very New Tandem Repeat
D. Viral Nucleotide Tandem Region

Correct Answer: B
Explanation: VNTRs differ in number among individuals.

Q44. Which technique separates DNA fragments by size?

A. Blotting
B. Hybridisation
C. Gel electrophoresis
D. Sequencing

Correct Answer: C
Explanation: Gel electrophoresis separates DNA based on size.

Q45. DNA fingerprinting is NOT useful in:

A. Forensics
B. Paternity testing
C. Wildlife conservation
D. Protein synthesis

Correct Answer: D
Explanation: It is used for identification, not protein synthesis.

Section J: Integrated & Board-Oriented MCQs

Q46. Central dogma describes flow of information from:

A. RNA → DNA → Protein
B. DNA → RNA → Protein
C. Protein → RNA → DNA
D. DNA → Protein → RNA

Correct Answer: B
Explanation: Genetic information flows from DNA to RNA to protein.

Q47. Which enzyme synthesises RNA primer?

A. Ligase
B. Helicase
C. Primase
D. Polymerase

Correct Answer: C
Explanation: Primase initiates DNA synthesis.

Q48. Which mutation is silent?

A. Frameshift
B. Nonsense
C. Missense
D. Synonymous

Correct Answer: D
Explanation: Synonymous mutation does not change amino acid.

Q49. Which feature prevents overlapping of genetic code?

A. Degeneracy
B. Universality
C. Comma-less nature
D. Mutability

Correct Answer: C
Explanation: Codons are read continuously without overlap.

Q50. Molecular Basis of Inheritance primarily explains:

A. Cell division
B. Protein folding
C. Flow and expression of genetic information
D. Evolution only

Correct Answer: C
Explanation: The chapter focuses on how genetic information is stored, replicated, expressed, and regulated.

✔ Strictly NCERT-Based | ✔ CBSE Board Pattern | ✔ Concept-Clearing MCQs

🎯 Targeting Exams Section

This MCQ set is structured to support preparation for:

• CBSE Class 12 Biology Board Examination

• CBSE Pre-Board & Unit Tests

• CBSE Compartment / Improvement Exams

• NEET (UG) – Concept Strengthening Level

• Other State Board Exams following NCERT syllabus

Questions are aligned with the latest CBSE competency-based MCQ pattern, emphasizing conceptual clarity, application, and analytical thinking.

🔑 Related Keyphrases 

• CBSE Class 12 Biology Molecular Basis MCQs

• Molecular Basis of Inheritance MCQ Questions

• NCERT Class 12 Biology MCQs with Answers

• DNA Replication Transcription Translation MCQs

• Genetic Code and Lac Operon MCQs

• Human Genome Project MCQs Class 12

• DNA Fingerprinting MCQs for CBSE

• Genetics and Evolution MCQs Class 12