Molecular Basis of Inheritance Class 12 Important Questions with Answers 2026-27 | Biology Chapter 5 Skip to content
🪔 शुभ नवरात्रि! Navratri Mega Sale Up to 34% off every pack + extra 15% off on 2 or more Shop the sale
Smart Notes for Every Exam · instant PDF download after payment +91 88240 98091
Home › Important questions › Class 12 Biology › Chapter 5
Class 12 · Biology · Chapter 5

Molecular Basis of Inheritance: Class 12 Important Questions with Answers

72 important questions for Class 12 Biology Chapter 5, Molecular Basis of Inheritance, the way they come in the board exam: MCQs, assertion–reason, case-based and short and long answer questions, with answers. Taken from our Class 12 Biology notes for 2026-27.

Cover of Complete Biology Notes for Class 12 (NCERT 2026-27, CBSE Board 2027)
Complete Class 12 Biology notes: all 13 chapters, every answer step by step
₹199₹24920% off
Free sample

Jump to: Practice set: test yourself20 MCQsAssertion–ReasonAnswers to the practice set

Practice set: test yourself

Try every question before looking at the answers below. 64 or more out of 80 means you are ready for the board.

A. Fill in the blanks (1 mark each)

  1. The bond between base and sugar is the ______ bond.
  2. A=T pairs have ___ hydrogen bonds.
  3. Histones are rich in lysine and ______.
  4. Hershey and Chase labelled protein with ______.
  5. Okazaki fragments are joined by ______.
  6. RNA polymerase II makes ______.
  7. The initiator codon is ______.
  8. In lac operon, the z gene codes for ______.

B. True or false? (1 mark each)

  1. RNA is more stable than DNA.
  2. The coding strand is copied into RNA.
  3. The genetic code is degenerate.
  4. Stop codons have specific tRNAs.
  5. The lac operon is under negative regulation.
  6. Less than 2% of the human genome codes for proteins.
  7. Satellite DNA codes for proteins.
  8. Meselson and Stahl used CsCl density gradient.

C. Very short answer (1 mark each)

  1. Name the scientists who gave X-ray data of DNA.
  2. Length of DNA in a human haploid cell (bp).
  3. What is a cistron?
  4. Name the three stop codons.
  5. Which rRNA acts as a ribozyme in bacteria?
  6. What is a nucleosome made of?
  7. Expand VNTR.
  8. Which chromosome has the most genes?
  9. Name the factor that ends transcription in bacteria.
  10. Give the full form of YAC.

D. Short answer I (2 marks each)

  1. Distinguish euchromatin and heterochromatin.
  2. Why is only one DNA strand transcribed?
  3. State two properties of the genetic code.
  4. What is the role of the 5′ cap and poly-A tail?
  5. What are UTRs and where are they found?
  6. Why is DNA a better genetic material than RNA?
  7. What is the significance of the 2′-OH group in RNA?
  8. Why is the lac operon said to be regulated at the transcriptional level?
My score (fill in after checking the answers)
SectionA /8B /8C /10D /16E /18F /20G (bonus)Total /80
My marks

Rough work

E. Short answer II (3 marks each)

  1. Describe the Meselson–Stahl experiment and its result after 40 minutes.
  2. Explain the steps of translation.
  3. Describe the processing of hnRNA in eukaryotes.
  4. Describe the features of the double helix model.
  5. Give three goals of the Human Genome Project.
  6. List the steps of DNA fingerprinting.

F. Long answer (5 marks each)

  1. Describe Griffith's experiment and the work of Avery, MacLeod and McCarty.
  2. Explain the lac operon with labelled diagrams in the presence and absence of lactose.

G. HOTS (higher-order thinking)

  1. Why is replication not done along the whole DNA at once?
  2. A mutation changes one base in a codon but the protein is unchanged. Why?
  3. Why do bacteria need no capping and tailing?
  4. Why can identical twins not be told apart by DNA fingerprinting?

20 MCQs

  1. A nucleoside contains
    (a) base + phosphate (b) sugar + phosphate (c) base + sugar (d) base + sugar + phosphate
  2. Purines are
    (a) A and G (b) C and T (c) U and C (d) A and T
  3. DNA with 30% A has G =
    (a) 30% (b) 70% (c) 40% (d) 20%
  4. Distance between base pairs
    (a) 3.4 nm (b) 0.34 nm (c) 34 nm (d) 2 nm
  5. The histone octamer has
    (a) 4 histones (b) 2 each of H2A, H2B, H3, H4 (c) H1 only (d) 6 histones
  6. Transforming principle was first shown by
    (a) Avery (b) Meselson (c) Hershey (d) Griffith
  7. ³²P labels
    (a) DNA (b) protein (c) lipid (d) carbohydrate
  8. After 2 generations in ¹⁴N, hybrid : light =
    (a) 1 : 3 (b) all hybrid (c) 1 : 1 (d) 1 : 7
  9. Substrate of DNA polymerase
    (a) NTPs (b) NMPs (c) amino acids (d) dNTPs
  10. Lagging strand is synthesised
    (a) continuously (b) discontinuously (c) 3′→5′ (d) not at all
  11. rRNAs (28S, 18S, 5.8S) are made by
    (a) pol II (b) pol III (c) pol I (d) reverse transcriptase
  12. Splicing removes
    (a) introns (b) exons (c) caps (d) tails
  13. Number of codons coding amino acids
    (a) 64 (b) 61 (c) 20 (d) 3
  14. UUU codes for
    (a) Met (b) Leu (c) Phe (d) stop
  15. The anticodon is on
    (a) mRNA (b) DNA (c) rRNA (d) tRNA
  16. Permease is coded by the gene
    (a) y (b) z (c) a (d) i
  17. Inducer of the lac operon
    (a) lactose (b) glucose (c) galactose (d) repressor
  18. HGP was completed in
    (a) 1990 (b) 1953 (c) 2006 (d) 2003
  19. Single-base DNA differences
    (a) VNTRs (b) SNPs (c) ESTs (d) BACs
  20. DNA fingerprinting was developed by
    (a) Watson (b) Sanger (c) Alec Jeffreys (d) Khorana

1 (c) · 2 (a) · 3 (d) · 4 (b) · 5 (b) · 6 (d) · 7 (a) · 8 (c) · 9 (d) · 10 (b) · 11 (c) · 12 (a) · 13 (b) · 14 (c) · 15 (d) · 16 (a) · 17 (a) · 18 (d) · 19 (b) · 20 (c)

Assertion–Reason (6)

(a) Both true, R explains A. (b) Both true, R does not explain A. (c) A true, R false. (d) A false, R true.

  1. A: DNA is more stable than RNA. R: RNA has a reactive 2′-OH group.
  2. A: Replication is semi-conservative. R: Each daughter DNA has one parental strand.
  3. A: The lagging strand is made discontinuously. R: DNA polymerase works only 5′→3′.
  4. A: The genetic code is universal. R: Some amino acids have more than one codon.
  5. A: Bacterial mRNA needs splicing. R: Eukaryotic genes are split genes.
  6. A: Satellite DNA is used in fingerprinting. R: It shows a high degree of polymorphism.

Key: 1 (a) · 2 (a) · 3 (a) · 4 (b) · 5 (d) · 6 (a)

Answers to the practice set

A. 1. N-glycosidic 2. two 3. arginine 4. ³⁵S 5. DNA ligase 6. hnRNA (precursor of mRNA) 7. AUG 8. β-galactosidase

B. 1. F 2. F (template strand) 3. T 4. F 5. T 6. T 7. F 8. T

C. 1. Maurice Wilkins and Rosalind Franklin 2. 3.3 × 10⁹ bp 3. a DNA segment coding for one polypeptide 4. UAA, UAG, UGA 5. 23S rRNA 6. a histone octamer with about 200 bp of DNA wrapped around it 7. variable number of tandem repeats 8. chromosome 1 9. ρ (rho) factor 10. yeast artificial chromosome

D. 1. Euchromatin: loosely packed, light-staining, transcriptionally active; heterochromatin: densely packed, dark-staining, inactive 2. Both strands would give two different proteins from one segment, and complementary RNAs would form non-translatable dsRNA 3. Any two: triplet, unambiguous, degenerate, universal, no punctuation, AUG initiator 4. Cap and tail make the mRNA stable and help its transport and translation 5. Untranslated regions of mRNA, before the start codon (5′) and after the stop codon (3′); needed for efficient translation 6. Double-stranded, thymine in place of uracil, no 2′-OH: chemically less reactive and more stable, mutates slowly 7. It makes RNA reactive, labile and easily degraded (and catalytic) 8. The repressor controls whether RNA polymerase can start transcription at the promoter

Answers to E, F, G, case study (short, long and HOTS answers, step by step) are in the notes pack

Revise Molecular Basis of Inheritance fully before the exam

  • Complete chapter notes with diagrams, equations and the points examiners give marks for
  • NCERT exercises and CBSE board questions, fully solved
  • Every practice answer (short, long, HOTS and case-based), step by step
  • Instant PDF download, colour and black & white print copies
See real pages (free sample)
← Principles of Inheritance and Variation Evolution →