Inside this set you will find the full CBSE and NEET question history for Molecular Basis of Inheritance, from base-pair MCQs to the classic experiment write-ups.
- 1-mark questions: 88 questions, the largest band, including base-pair calculations, MCQ and assertion-reason from recent papers.
- 2 and 3-mark questions: 25 and 41 questions, built around DNA replication, the genetic code and transcription.
- 5-mark long answers: 40 questions, where the landmark experiments and the lac operon appear again and again.
The Class 12 Biology Molecular Basis of Inheritance PYQ compilation gathers 199 board-paper questions across 2008 to 2026, sorted by marks and by year for ordered, exam-style practice.
Every question in this Class 12 Biology Molecular Basis of Inheritance PYQ compilation is sourced from CBSE board papers (Delhi, Outside Delhi, Foreign and Compartment) and cross-checked against the official mark scheme, with near-duplicate questions removed.
What the Molecular Basis of Inheritance Previous Year Questions Cover
The 199-question set maps every concept the NCERT chapter introduces. The landmark experiments (Griffith, Avery, Hershey-Chase and Meselson-Stahl) drive a big share of the 5-mark band. DNA replication and the replication fork carry many 3 and 5-mark answers. The genetic code, transcription and translation appear across all bands, while chromatin and the nucleosome, the lac operon and DNA fingerprinting fill the higher-order and short-answer items.
Marks-wise Distribution of the Molecular Basis of Inheritance PYQs
The table below shows how the 199 questions split across the CBSE marks bands. Use it to decide how much revision time each band deserves.
| Marks | Questions | Total Marks | CBSE Section | Type |
|---|---|---|---|---|
| 1 mark | 88 | 88 | Section A | MCQ / Assertion-Reason |
| 2 mark | 25 | 50 | Section B | VSA (Very Short Answer) |
| 3 mark | 41 | 123 | Section C | SA (Short Answer) |
| 4 mark | 5 | 20 | Section D | Case Study |
| 5 mark | 40 | 200 | Section E | Long Answer |
Year-wise Spread of Class 12 Biology Molecular Basis of Inheritance PYQs
The compilation draws from 16 CBSE board years. Roughly 58% of the questions come from 2023 onwards, and 2025 alone added 47 questions, the single largest year in this chapter.
- 2026: A 140-base-pair guanine count from the thymine percentage, a Hershey-Chase style radioactive thymidine problem, and why the genetic code is called universal.
- 2024 to 2025: The largest contribution years, with banks of base-pair calculations, replication-fork and genetic-code MCQs.
- 2020 to 2023: Reduced-syllabus papers, yet semi-conservative replication, transcription and the lac operon still feature.
- 2008 to 2019: Long answers on the Hershey-Chase and Meselson-Stahl experiments and chromatin structure, all still in the current syllabus.
Topic Frequency in the Molecular Basis of Inheritance Board Paper Questions
The 199 questions cluster into the six topic buckets below, ranked by how often CBSE has set them between 2008 and 2026.
| Rank | Topic Cluster | Frequency | Typical Marks Band |
|---|---|---|---|
| 1 | Landmark experiments (Griffith, Avery, Hershey-Chase, Meselson-Stahl, DNA as genetic material) | ~22 per cent | 3 and 5 mark |
| 2 | DNA structure and replication (base pairing, semi-conservative replication, replication fork, polarity) | ~20 per cent | 1, 3, 5 mark |
| 3 | Genetic code and translation (codons, tRNA as adaptor, AUG, degeneracy, universality) | ~18 per cent | 1, 2, 3 mark |
| 4 | Transcription (RNA polymerase, hnRNA, splicing, capping and tailing) | ~15 per cent | 2 and 3 mark |
| 5 | Chromatin and DNA packaging (nucleosome, histones, euchromatin and heterochromatin) | ~13 per cent | 1, 2, 5 mark |
| 6 | Lac operon and DNA fingerprinting (gene regulation, satellite DNA, applications) | ~12 per cent | 3 and 5 mark |
Marks-Band Attempt Strategy for the Molecular Basis of Inheritance PYQs
The 199 PYQs are arranged marks-ascending inside the PDF so you can attempt them in the same order the CBSE paper presents them.
- 1-mark questions: Spend no more than 45 seconds each. With 88 here, base-pair sums and code facts must become automatic.
- 2-mark questions: A short definition or one step of transcription. Aim for 3 minutes.
- 3-mark questions: Usually the genetic code, replication fork or an experiment summary. State the conclusion of each landmark experiment in one clear line.
- 5-mark long answers: A full experiment write-up or the lac operon mechanism. Allocate 12 to 15 minutes.
Recent CBSE Trend: 2024 to 2026 Pattern Shift in Molecular Basis of Inheritance
Three things have changed in the recent CBSE cycles that the Molecular Basis of Inheritance previous year questions now reflect:
- Section A now carries a fixed block of 1-mark questions, including numerical base-pair problems. The compilation includes 88 such questions, the largest 1-mark band of any Biology chapter.
- Numerical and applied questions are rising, for example the 2026 problem asking for the guanine count in a 140-base-pair DNA with 20 per cent thymine.
- 5-mark questions almost always carry an OR alternative, so the PDF keeps both branches, often pairing an experiment with a replication or transcription answer.
Sample Previous Year Questions from Molecular Basis of Inheritance
Here are a few real previous year questions from the Molecular Basis of Inheritance board papers, taken straight from the compilation. The full set is in the downloadable PDF.
A DNA molecule is 140 base pairs long. It has 20% thymine. How many guanine bases are present in the molecule?
- 64
- 84
- 32
- 56
[2026 • 1 mark]
A bacterium having radioactive thymidine in its DNA is allowed to multiply in a medium having non-radioactive thymidine for two generations. What percentage of bacteria will have radioactive thymidine in its DNA?
- 100
- 50
- 75
- 25
[2026 • 1 mark]
(a) What is a genetic code? (b) Why did scientists feel the need to propose a genetic code? (c) Genetic code is said to be 'Universal'. Why?
[2026 • 3 mark]
Common Mistakes in the Molecular Basis of Inheritance Board Questions
- Applying Chargaff's rule wrongly in base-pair sums, so A is not paired with T and G with C correctly.
- Confusing the conclusions of the Hershey-Chase and Meselson-Stahl experiments.
- Writing replication as conservative or dispersive instead of semi-conservative.
- Mixing up transcription and translation, or naming the wrong enzyme for each step.
- Describing the lac operon without the regulator gene, operator and the role of lactose as the inducer.
Student Feedback on Molecular Basis of Inheritance PYQ Practice
- 69 per cent said the landmark experiments and the lac operon were the hardest part of the 5-mark band.
- 56 per cent reported gaining 5 to 8 marks after solving all 40 five-mark PYQs from this PDF before the boards.
- 45 per cent said a genetic-code or base-pair calculation appeared in their actual 2026 paper.
- Average time to finish all 199 PYQs: about 15 hours across 8 study sessions.
How These PYQs Pair with the Other Molecular Basis of Inheritance Resources
Solving previous year questions alone gives you only half the prep. Pair the PYQ PDF with the matching concept, formula and solution resources for Molecular Basis of Inheritance.
| Resource | What It Gives You | Open |
|---|---|---|
| NCERT Solutions | Step-by-step worked answers to every NCERT back-exercise question of Molecular Basis of Inheritance | NCERT Solutions for Molecular Basis of Inheritance |
| Notes | Concept revision notes covering every topic in the Molecular Basis of Inheritance chapter | Molecular Basis of Inheritance Class 12 Notes |
| Formula Sheet | All key formulas and results of Molecular Basis of Inheritance on one page for last-day revision | Molecular Basis of Inheritance Formula Sheet |
| Handwritten Notes | Scanned handwritten notes of Molecular Basis of Inheritance for quick one-shot revision | Molecular Basis of Inheritance Handwritten Notes |
| Exemplar Solutions | NCERT Exemplar problems of Molecular Basis of Inheritance solved in full for extra practice | NCERT Exemplar Solutions for Molecular Basis of Inheritance |
| NCERT Book | Official NCERT Molecular Basis of Inheritance chapter PDF for free download | Molecular Basis of Inheritance NCERT Book PDF |
| Exemplar Book | NCERT Exemplar Molecular Basis of Inheritance problem book PDF for free download | Molecular Basis of Inheritance Exemplar Book PDF |
How to Use the Molecular Basis of Inheritance PYQ PDF Most Effectively
The 199 questions are sequenced for a three-pass revision plan:
- Pass 1 (Day 1 to 2): Attempt all 88 one-mark questions. Drill the base-pair sums and the genetic-code facts until they are automatic.
- Pass 2 (Day 3 to 5): Solve the 25 two-mark and 41 three-mark questions on replication, transcription and the genetic code.
- Pass 3 (Day 6 to 10): Work through the 40 five-mark long answers, writing the landmark experiments and the lac operon mechanism in full.
All Class 12 Biology Chapter PYQ PDFs
Every Class 12 Biology chapter has its own PYQ compilation built the same way, sorted by marks and tagged by year.
| Chapter | Topic | Previous Year Questions |
|---|---|---|
| Chapter 1 | Sexual Reproduction in Flowering Plants | PYQ PDF |
| Chapter 2 | Human Reproduction | PYQ PDF |
| Chapter 3 | Reproductive Health | PYQ PDF |
| Chapter 4 | Principles of Inheritance and Variation | PYQ PDF |
| Chapter 5 | Molecular Basis of Inheritance | PYQ PDF |
| Chapter 6 | Evolution | PYQ PDF |
| Chapter 7 | Human Health and Disease | PYQ PDF |
| Chapter 8 | Microbes in Human Welfare | PYQ PDF |
| Chapter 9 | Biotechnology: Principles and Processes | PYQ PDF |
| Chapter 10 | Biotechnology and its Applications | PYQ PDF |
| Chapter 11 | Organisms and Populations | PYQ PDF |
| Chapter 12 | Ecosystem | PYQ PDF |
| Chapter 13 | Biodiversity and Conservation | PYQ PDF |
Also Check: NCERT Solutions for Class 12 Biology
Class 12 Biology Molecular Basis of Inheritance PYQ FAQs
Ques. How many previous year questions are in the Class 12 Biology Molecular Basis of Inheritance PYQ PDF?
Ans. The PDF has 199 previous year questions from CBSE board papers between 2008 and 2026, sorted by marks (1 to 5) and then by year, latest first. Near-duplicate questions across sets and years are removed so the same question never repeats.
Ques. Are the Molecular Basis of Inheritance PYQs based on the 2026-27 CBSE syllabus?
Ans. Yes. Every question follows the 2026-27 CBSE Class 12 Biology syllabus. Older long-form questions are kept because the core ideas, like the landmark experiments, replication and the genetic code, are unchanged in the current syllabus.
Ques. Which topics of Molecular Basis of Inheritance appear most often in CBSE board papers?
Ans. From the 199-question set: the landmark experiments (about 22 per cent), DNA structure and replication (about 20 per cent), the genetic code and translation (about 18 per cent), transcription (about 15 per cent), and chromatin and the nucleosome.
Ques. How is this PYQ PDF different from a CBSE sample paper?
Ans. A sample paper gives you one paper. This PDF stitches together 16 years of questions across every set and region (Delhi, Outside Delhi, Foreign and Compartment) for Molecular Basis of Inheritance alone, so you can see which experiments and concepts CBSE repeats.
Ques. Does the Molecular Basis of Inheritance PYQ PDF include MCQs?
Ans. Yes. 88 of the 199 questions are 1-mark questions, the largest 1-mark band of any Biology chapter, including base-pair calculations, MCQ and assertion-reason from 2023 onwards.
Ques. Where can I download the Molecular Basis of Inheritance Class 12 PYQ PDF for free?
Ans. The full Molecular Basis of Inheritance PYQ PDF is free to download from the PDF button at the top of this page. No sign-up is needed.
Ques. How should I use these PYQs to revise Molecular Basis of Inheritance in the last 10 days?
Ans. Use the three-pass plan: Day 1 to 2 attempt all 88 one-mark questions, Day 3 to 5 solve the 2 and 3-mark questions, Day 6 to 10 attempt all 40 long answers under a 12-minute timer. State each experiment's conclusion in one clear line.
Ques. Does the PDF give answers or only the questions?
Ans. The PDF gives every question with a full step-by-step solution, sorted by marks and year, so you can attempt each one like a practice paper and then check the worked answer.
Ques. Are the landmark experiments important for the CBSE Molecular Basis of Inheritance questions?
Ans. Very. The landmark experiments make up close to a quarter of all the questions in this PDF, especially in the 5-mark band. Knowing the aim, method and conclusion of Hershey-Chase and Meselson-Stahl is the best use of your time for this chapter.
Ques. What is semi-conservative DNA replication?
Ans. Semi-conservative DNA replication means each new DNA molecule has one old (parent) strand and one newly made strand. The two strands of the parent DNA separate and each acts as a template. Meselson and Stahl proved this model using heavy nitrogen labelling in E. coli.
Ques. How is the genetic code defined?
Ans. The genetic code is the set of rules by which the base sequence in mRNA is read as a sequence of amino acids. It is read in triplets called codons. The code is universal, degenerate (more than one codon per amino acid) and unambiguous, and AUG is the start codon.
Ques. What is a nucleosome?
Ans. A nucleosome is the basic unit of DNA packaging in a eukaryotic cell. It is made of about 200 base pairs of DNA wrapped around a core of eight histone proteins (a histone octamer). Many nucleosomes joined together give chromatin its 'beads-on-a-string' appearance.
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