Molecular Basis of Inheritance — Class 12 MCQs with Answers
Class 12 CBSE Biology · Chapter 5
90 practice questions · 30 Easy · 30 Medium · 30 Hard · Updated
Practise the most important Class 12 CBSE Biology questions from Chapter 5, "Molecular Basis of Inheritance". You get 9 timed quizzes made from 90 NCERT-based MCQs, with answers and explanations. The questions are split into 30 Easy, 30 Medium and 30 Hard. Warm up on the basics, then move on to the exam-level questions that set top scorers in CBSE & Maharashtra HSC Board exams, MHT-CET and NEET UG apart.
To score well in "Molecular Basis of Inheritance", focus on diagrams, key terms and knowing NCERT line by line. Each MCQ here is timed and uses exam-style marking (+4 correct, −1 wrong, 0 skipped). This trains you to stay accurate under time pressure, as real papers need. Every question has a short explanation, so a wrong answer becomes a quick lesson. It is the fastest way to fix gaps before a test.
Use this chapter for focused revision. Start with the Easy set to check your basics on Molecular Basis of Inheritance, then move to Medium and Hard to practise applying them. Your accuracy, streaks and XP save automatically. This chapter also adds to your overall Class 12 Biology mastery score. 14 sample questions are solved in full below, with the answer and a worked explanation. Sign in free to start practising.
Key concepts: Molecular Basis of Inheritance (Class 12 Biology)
Molecular basis of inheritance: DNA as the genetic material (Griffith, Hershey-Chase), the Watson-Crick double helix and Chargaff's rule, DNA packaging into nucleosomes, semiconservative replication, transcription, the genetic code, translation, the lac operon, and the Human Genome Project and DNA fingerprinting.
- DNA double helix
- Two antiparallel strands in a right-handed helix; sugar-phosphate backbone outside, base pairs (A=T, G≡C) inside. B-DNA has ~10 bp per 3.4 nm turn.
- Chargaff's rule
- In any double-stranded DNA, adenine equals thymine and guanine equals cytosine (A=T, G=C), so purines equal pyrimidines (A+G = T+C).
- Nucleosome
- Repeating unit of chromatin — about 200 bp of DNA wrapped around a histone octamer; histones are positively charged (rich in lysine, arginine).
- Transforming principle
- Griffith showed a heat-killed virulent strain could transform a live avirulent one; Avery, MacLeod and McCarty identified the transforming agent as DNA.
Molecular Basis of Inheritance — important questions & MCQs with answers (Class 12 Biology)
14 solved questions from this chapter's difficulty levels, each with its answer and explanation. The other 76 are timed and scored when you sign in.
- Q1Easy
DNA double helix model proposed by:
A.MendelB.Watson and Crick✓ CorrectC.DarwinD.PasteurAnswer: B. Watson and Crick
Explanation: Watson and Crick built the double-helix model in 1953 using Rosalind Franklin's X-ray diffraction photo 51; Franklin generated the key data but is often left out of this answer.
- Q2Easy
Central dogma:
A.RandomB.Protein → DNAC.RNA → DNA onlyD.DNA → RNA → Protein✓ CorrectAnswer: D. DNA → RNA → Protein
Explanation: The central dogma states DNA to RNA to Protein: transcription copies DNA into RNA, translation reads RNA into protein. Information never flows from protein back into DNA or RNA.
- Q3Easy
The double-helix model of DNA was proposed by:
A.MendelB.Watson and Crick✓ CorrectC.MorganD.Hershey and ChaseAnswer: B. Watson and Crick
Explanation: Watson and Crick proposed the DNA double helix in 1953, built on Rosalind Franklin's X-ray diffraction data; Hershey and Chase separately proved DNA, not protein, is the genetic material.
- Q4Easy
The process of synthesising RNA from a DNA template is:
A.TranslationB.Transcription✓ CorrectC.ReplicationD.SplicingAnswer: B. Transcription
Explanation: Transcription synthesises RNA using one DNA strand as template, via RNA polymerase; it is distinct from translation (RNA to protein) and replication (DNA to DNA).
- Q5Easy
The sugar present in DNA is:
A.Deoxyribose✓ CorrectB.RiboseC.GlucoseD.SucroseAnswer: A. Deoxyribose
Explanation: DNA's sugar is 2′-deoxyribose, lacking the 2′-OH found in RNA's ribose; that missing hydroxyl is exactly what makes DNA chemically more stable for long-term storage.
- Q6Easy
In RNA, thymine is replaced by:
A.GuanineB.CytosineC.Uracil✓ CorrectD.AdenineAnswer: C. Uracil
Explanation: RNA substitutes uracil for DNA's thymine; uracil still pairs with adenine, so codon-anticodon and base-pairing rules carry over unchanged despite the base swap.
- Q7Medium
DNA replication is:
A.ConservativeB.Semiconservative✓ CorrectC.DispersiveD.RandomAnswer: B. Semiconservative
Explanation: Meselson and Stahl showed replication is semiconservative: each daughter duplex keeps one parental strand and gains one newly synthesised strand, ruling out conservative or dispersive models.
- Q8Medium
Codon is:
A.Triplet of bases coding for one amino acid✓ CorrectB.Single baseC.Whole geneD.ProteinAnswer: A. Triplet of bases coding for one amino acid
Explanation: A codon is a triplet of three consecutive mRNA bases specifying one amino acid or a stop signal; with 4 bases at each of 3 positions, 4³ = 64 codons exist, not one base per amino acid.
- Q9Medium
The two strands of DNA are antiparallel, meaning one runs 5′→3′ and the other:
A.RandomlyB.5′→3′C.In the same directionD.3′→5′✓ CorrectAnswer: D. 3′→5′
Explanation: DNA's two strands run antiparallel: one is oriented 5′→3′, its partner runs 3′→5′ in the opposite direction — this opposite polarity is essential for correct base pairing along the helix.
- Q10Medium
During transcription, the DNA strand that is read (3′→5′) to make RNA is the:
A.Lagging strandB.Coding strandC.Sense strandD.Template strand✓ CorrectAnswer: D. Template strand
Explanation: RNA polymerase reads the template (antisense) strand 3′→5′ to build RNA 5′→3′; the coding (sense) strand instead matches the RNA sequence, with U swapped for T, and is not itself read.
- Q11Medium
In B-DNA, one complete turn of the helix (pitch) spans about ____ and contains about ____ base pairs.
A.0.34 nm; 10 bpB.3.4 nm; 10 bp✓ CorrectC.34 nm; 100 bpD.3.4 nm; 1 bpAnswer: B. 3.4 nm; 10 bp
Explanation: One turn of B-form DNA (its pitch) spans about 3.4 nm and contains roughly 10 base pairs, giving a rise of about 0.34 nm per base pair — don't confuse the pitch with the per-base rise.
- Q12Hard
PCR is used to:
A.Cut DNAB.Sequence proteinsC.Amplify DNA in vitro✓ CorrectD.Modify RNA onlyAnswer: C. Amplify DNA in vitro
Explanation: PCR (polymerase chain reaction) amplifies a specific DNA segment exponentially in vitro using heat-stable Taq polymerase and repeated denature-anneal-extend cycles; it does not sequence or cut DNA.
- Q13Hard
Lac operon model proposed by:
A.Watson and CrickB.Jacob and Monod✓ CorrectC.MendelD.DarwinAnswer: B. Jacob and Monod
Explanation: Jacob and Monod proposed the lac operon model in 1961 to explain inducible gene regulation in E. coli, where lactose switches on the structural genes z, y and a.
- Q14Hard
If a double-stranded DNA has 20% adenine, the percentage of guanine is:
A.30%✓ CorrectB.20%C.40%D.60%Answer: A. 30%
Explanation: By Chargaff's rule A=T, so 20% adenine means 20% thymine, leaving G+C=60%; since G=C, guanine is 30% — don't assume all four bases sit at equal percentages.
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Start this chapter free →Molecular Basis of Inheritance — FAQs
What are the key concepts in Class 12 Biology Molecular Basis of Inheritance?+
Molecular basis of inheritance: DNA as the genetic material (Griffith, Hershey-Chase), the Watson-Crick double helix and Chargaff's rule, DNA packaging into nucleosomes, semiconservative replication, transcription, the genetic code, translation, the lac operon, and the Human Genome Project and DNA fingerprinting. Key ideas include DNA double helix, Chargaff's rule, Nucleosome, Transforming principle.
What does Class 12 Biology Chapter 5 (Molecular Basis of Inheritance) cover on XamBaaz?+
It has 90 NCERT-based MCQs on "Molecular Basis of Inheritance": 30 Easy, 30 Medium and 30 Hard. Together they make 9 timed quizzes, and you never get the same set twice. Every question has an instant explanation. They help you prepare for CBSE & Maharashtra HSC Board exams, MHT-CET and NEET UG.
Are these "Molecular Basis of Inheritance" questions free to practise?+
Yes. Sign in with Google to practise "Molecular Basis of Inheritance" free. Full unlimited access is ₹999/year on a launch offer until 1 December 2026. No chapter is charged separately.
How should I revise "Molecular Basis of Inheritance" for the exam?+
Start with the Easy quiz to check your basics, then try Medium and Hard to practise applying them. There are 9 timed quizzes on this chapter, so you can come back for a fresh set instead of one you have seen. Read each explanation, retry the questions you miss, and track your accuracy until it stays high.
Are these "Molecular Basis of Inheritance" MCQs available with answers?+
Yes. 14 sample questions are shown here in full, each with the correct option and a step-by-step "Why" explanation. Sign in free with Google to start practising, with instant scoring.
Is there negative marking in the "Molecular Basis of Inheritance" quizzes?+
Yes. The timed quizzes use exam-style marking: +4 for a right answer, −1 for a wrong one and 0 for a skip, the same negative marking as NEET UG. MHT-CET and CBSE board papers have no negative marking. Our mocks for those are scored their way.
What are the important questions from Molecular Basis of Inheritance (Class 12 Biology)?+
The questions that matter most test DNA double helix, Chargaff's rule, Nucleosome, Transforming principle. This page shows 14 solved important MCQs with answers and explanations; all 90 questions on the chapter are available as timed quizzes once you sign in.
Is there an online quiz for Molecular Basis of Inheritance?+
Yes — Class 12 Biology Molecular Basis of Inheritance has timed online quizzes at Easy, Medium and Hard levels, with instant scoring and a worked explanation on every question. The first quiz on the chapter is free.