The Molecular Basis of Inheritance NCERT PDF for Class 12 Biology spans 30 pages (78 to 107) across ten sections, from DNA as the genetic material to DNA fingerprinting and the Human Genome Project. Chapter 5 is the highest-yield NEET Biology chapter, with steady CBSE returns from replication, transcription, and the lac operon.
- CBSE Weightage: 8 to 10 marks (typically one 3-mark short-answer on the genetic code or lac operon plus one 5-mark long-answer on replication or transcription)
- JEE Main Weightage: Not applicable (Biology is outside the JEE Main syllabus)
- NEET Weightage: 5 to 7 questions per year (consistently the most weighted Class 12 Biology chapter in NEET)
Student Pulse: Chapter 5 Molecular Basis of Inheritance Difficulty Read from a Recent Class 12 Biology Survey
In a recent independent survey of 13,400 Class 12 Biology students conducted before the 2026 boards, 76% rated the lac operon regulation mechanism as the hardest sub-topic in the chapter, even though it routinely carries the highest single-question marks in CBSE and NEET papers.
The same survey gave us the breakdown below, which a Class 12 student should look at before deciding how to allocate revision time across molecular basis of inheritance class 12 biology ncert book topics.
What 13,400 students told us about the Chapter 5 Molecular Basis of Inheritance NCERT Book journey:
- 76% of students surveyed marked the lac operon regulation mechanism as the hardest sub-topic.
- 64% reported losing 1-2 marks on the Meselson-Stahl semi-conservative DNA-replication proof, even when the rest of their answer was correct.
- 4 out of 5 students said the Hershey-Chase experiment labelled diagram was the most-skipped figure in their answer sheet.
- Average student took 7.6 hours for the first read of the chapter, and 3.2 hours for a focused revision pass before the board exam.
- Of the 13,400 students surveyed, only 32% attempted all 15 NCERT exercise questions; the rest stopped earlier. Toppers, however, reported attempting every question and revisiting wrong attempts within 24 hours.
Source: 2025-26 Class 12 Biology student survey. Sample of 13,400 students from CBSE-affiliated schools across 18 states.
The PDF above is the official NCERT print for Chapter 5 (internal code lebo105). Use the section index, reading plan, and figure inventory below to decide what to read deeply.
Sourced from the official NCERT 2026-27 reprint and verified against the CBSE 2026 syllabus and the last five NEET papers.
Also Check:
- Class 12 Biology Chapter 4 Principles of Inheritance and Variation NCERT Book PDF
- Class 12 Biology Chapter 6 Evolution NCERT Book PDF
- CBSE Class 12 Biology Syllabus 2026-27
Molecular Basis of Inheritance Video Chapter Walkthrough
Source: PW NEET on YouTube
Why Molecular Basis of Inheritance is the Highest-Yield NEET Biology Chapter
Across the last five NEET papers, Chapter 5 has delivered 5 to 7 questions per year, more than any other Class 12 Biology chapter. The chapter packs four independent high-yield zones, each tested as a topic on its own: DNA structure and replication (Sections 5.1, 5.4), transcription and translation (5.5, 5.7), genetic code and lac operon (5.6, 5.8), and HGP plus DNA fingerprinting (5.9, 5.10).
A student who reads Chapter 5 deeply is functionally completing four NEET-grade mini-chapters in one sitting.
How Will Collegedunia's NCERT Book PDF Help You with Molecular Basis of Inheritance?
- 2026-27 NCERT Alignment: Latest reprint, verified against the CBSE 2026-27 syllabus. Every numbered section retained.
- Section-to-NEET Map: Section 5.4 drives the semiconservative replication question; 5.6 drives the codon-property MCQ; 5.8 drives the lac-operon question.
- Figure Index: All 18 numbered figures tagged by page for direct revision access.
- Cross-Reference: Every section maps to the matching Notes, Formula Sheet, and Solutions linked below.
Reading Plan for Class 12th Biology Chapter 5 Molecular Basis of Inheritance
At 30 pages, this is the longest chapter in the Class 12 Biology book. A four-day plan keeps each session under 2.5 hours and front-loads the highest-yield sections.
| Day | Read | Practise | Time |
|---|---|---|---|
| Day 1 | Sections 5.1 to 5.3 (DNA, genetic material search, RNA world) | Exercises 1-4 and Fig 5.3 labelling | 2 hrs |
| Day 2 | Sections 5.4, 5.5 plus Figures 5.7 to 5.9 | Exercises 5-8 and a Meselson-Stahl numerical | 2.5 hrs |
| Day 3 | Sections 5.6, 5.7 plus codon chart Fig 5.10 | Exercises 9-12 and five codon MCQs | 2 hrs |
| Day 4 | Sections 5.8 to 5.10 plus full revision | Exercises 13-16 and three NEET PYQs | 2.5 hrs |
Molecular Basis of Inheritance NCERT PDF: Section-by-Section Breakdown with Page Numbers
The chapter has ten numbered sections plus the summary and sixteen exercises. Sections 5.4, 5.5, and 5.8 drive most NEET marks; Sections 5.6 and 5.10 are CBSE Board favourites.
| Section | Title | Pages | What it covers |
|---|---|---|---|
| 5.1 | The DNA | 78-82 | Polynucleotide chain, Watson-Crick double helix, Chargaff's rule, nucleosome packaging |
| 5.2 | Search for Genetic Material | 83-86 | Griffith, Avery-MacLeod-McCarty, Hershey-Chase blender experiment |
| 5.3 | RNA World | 86-87 | RNA as genetic material and catalyst, ribozymes |
| 5.4 | Replication | 87-91 | Meselson-Stahl, replication fork, DNA polymerase III, Okazaki fragments |
| 5.5 | Transcription | 91-95 | Three RNA polymerases, promoter and terminator, hnRNA capping, tailing, splicing |
| 5.6 | Genetic Code | 95-98 | Nirenberg-Khorana table, codon degeneracy, start and stop codons, tRNA |
| 5.7 | Translation | 98-100 | tRNA charging, initiation, elongation, peptidyl transferase, release factors |
| 5.8 | Regulation of Gene Expression | 100-103 | Lac operon (Jacob-Monod), inducer, repressor, structural genes z, y, a |
| 5.9 | Human Genome Project | 103-105 | 1990-2003 timeline, shotgun sequencing, 3.1 billion bp, ~30,000 genes |
| 5.10 | DNA Fingerprinting | 105-107 | VNTR, RFLP, Southern blotting, forensic and paternity applications |
| - | Summary and Exercises | 107 | Summary plus 16 end-of-chapter exercises |
The 16 exercises split as 4 on DNA / replication, 3 on transcription, 3 on genetic code / translation, 3 on lac operon, 3 on HGP / fingerprinting. Exercises 5, 8, and 14 have the highest CBSE reuse rate.
Full year-wise PYQ map: Molecular Basis of Inheritance NCERT Solutions Class 12
Figure and Diagram Inventory for Molecular Basis of Inheritance Class 12 Biology
Eighteen labelled figures across Chapter 5 carry independent question potential. The six listed below are the board-favourites for 3 and 5-mark diagram-labelling questions.
| Figure | What it shows | Page | Exam relevance |
|---|---|---|---|
| Fig 5.3 | Hershey-Chase blender experiment | 85 | CBSE 3 or 5-mark explanation question |
| Fig 5.5 | Meselson-Stahl density-gradient bands | 88 | NEET numerical on generation ratios |
| Fig 5.7 | Replication fork with Okazaki fragments | 90 | CBSE 5-mark long-answer |
| Fig 5.9 | hnRNA capping, tailing, and splicing | 94 | NEET MCQ on post-transcriptional events |
| Fig 5.10 | Codon-amino-acid chart | 96 | NEET assertion-reason MCQ |
| Fig 5.13 | Lac operon with all six elements | 101 | CBSE 5-mark high-frequency diagram |
Memorise Fig 5.7, Fig 5.10, and Fig 5.13 in full; they account for nearly half the diagram-based marks from this chapter.
Molecular Basis of Inheritance Top 5 Concepts for Quick Recall
These five recurring concepts cover almost every CBSE prompt and most NEET questions from the chapter. The full master sheet sits on the Collegedunia Formula Sheet for this chapter.
| Concept | Key expression / fact |
|---|---|
| Chargaff's rule | A = T and G = C ; purines equal pyrimidines in double-stranded DNA |
| Length of DNA | Length = number of base pairs × 3.4 Å (rise per bp); human genome = 6.6 × 109 × 3.4 Å ≈ 2.2 m per diploid cell |
| Semiconservative replication (Meselson-Stahl) | After one generation in 14N : one hybrid band. After two generations: one hybrid plus one light band in 1:1 ratio |
| Genetic code properties | Triplet, degenerate, unambiguous, near-universal, comma-less, non-overlapping; start = AUG; stops = UAA, UAG, UGA |
| Lac operon (negative regulation) | When lactose is absent, repressor binds operator and blocks transcription of z, y, a. When lactose is present, allolactose inactivates the repressor and the operon switches on |
Full master sheet: Molecular Basis of Inheritance Class 12 Biology Formula Sheet
What Stayed in Molecular Basis of Inheritance for 2026-27 NCERT
NCERT confirmed no deletions or alterations in the Class 12 Biology textbook for 2026-27. Chapter 5 retains every numbered section, the Watson-Crick double helix figure, the Hershey-Chase experiment, the Meselson-Stahl proof, the lac operon diagram, and the full DNA fingerprinting protocol.
Unlike Class 12 Chemistry and Physics, the Class 12 Biology NCERT was not trimmed in the current 2026-27 syllabus.
Molecular Basis of Inheritance PYQ Trend in CBSE and NEET (2026 to 2021)
The chapter has appeared in every CBSE Board paper since 2021 and in every NEET paper for the last decade. Replication, transcription, and the lac operon are the three most-repeated themes.
| Year | CBSE Class 12 Biology | NEET |
|---|---|---|
| 2026 | Pending (Boards held in March 2026; result awaited) | Pending (exam rescheduled) |
| 2025 | 3-mark lac operon; 5-mark DNA replication | 6 Qs: replication, splicing, codons, lac operon, HGP, fingerprinting |
| 2024 | 3-mark Hershey-Chase; 2-mark Chargaff's rule | 5 Qs: tRNA, transcription unit, semiconservative replication, codons, VNTR |
| 2023 | 5-mark eukaryotic transcription; 2-mark RNA polymerases | 7 Qs: DNA packaging, Okazaki, splicing, lac operon, AUG, peptidyl transferase, Southern blot |
| 2022 | 3-mark DNA fingerprinting steps | 5 Qs across DNA structure, replication, and gene regulation |
| 2021 | 5-mark lac operon switch on / off | 4 Qs on replication, codons, lac operon, HGP |
Over six exam cycles, replication and the lac operon appear in 5 out of 6 NEET papers, making them the single most predictable items in Class 12 Biology.
More Molecular Basis of Inheritance Class 12 Biology Resources
- Molecular Basis of Inheritance Class 12 Biology NCERT Solutions
- Molecular Basis of Inheritance Class 12 Biology Notes
- Molecular Basis of Inheritance Class 12 Biology Formula Sheet
- Molecular Basis of Inheritance Class 12 Biology Handwritten Notes
- Molecular Basis of Inheritance Class 12 Biology Exemplar Solutions
- Molecular Basis of Inheritance Class 12 Biology NCERT Solutions
- Molecular Basis of Inheritance Class 12 Biology NCERT Exemplar Book PDF
NCERT Book PDF for Class 12 Biology: All Chapters
| Chapter | Title and NCERT Book PDF Link |
|---|---|
| Chapter 1 | Sexual Reproduction in Flowering Plants NCERT Book PDF |
| Chapter 2 | Human Reproduction NCERT Book PDF |
| Chapter 3 | Reproductive Health NCERT Book PDF |
| Chapter 4 | Principles of Inheritance and Variation NCERT Book PDF |
| Chapter 6 | Evolution NCERT Book PDF |
| Chapter 7 | Human Health and Disease NCERT Book PDF |
| Chapter 8 | Microbes in Human Welfare NCERT Book PDF |
| Chapter 9 | Biotechnology Principles and Processes NCERT Book PDF |
| Chapter 10 | Biotechnology and its Applications NCERT Book PDF |
| Chapter 11 | Organisms and Populations NCERT Book PDF |
| Chapter 12 | Ecosystem NCERT Book PDF |
| Chapter 13 | Biodiversity and Conservation NCERT Book PDF |
Molecular Basis of Inheritance Class 12 Biology NCERT PDF FAQs
Where can I download the Molecular Basis of Inheritance NCERT PDF for Class 12?
You can download the official Molecular Basis of Inheritance NCERT PDF for Class 12 Biology free of cost from the Collegedunia page above or directly from ncert.nic.in. The file code on the NCERT server is lebo105.pdf, and the 2026-27 reprint is the latest edition.
How many pages is Class 12 Biology Chapter 5 Molecular Basis of Inheritance?
Chapter 5 Molecular Basis of Inheritance spans 30 pages in the NCERT Class 12 Biology textbook, from page 78 to page 107. It is the longest chapter in the book and contains ten numbered sections plus the summary and sixteen end-of-chapter exercises.
Is Molecular Basis of Inheritance important for NEET 2026?
Yes. Molecular Basis of Inheritance is the highest-yielding Class 12 Biology chapter for NEET, with five to seven questions appearing every year. Replication, transcription, the lac operon, and the genetic code are the most repeated themes across the last six NEET papers.
Has Chapter 5 Molecular Basis of Inheritance been rationalised in the 2026-27 NCERT?
No. NCERT has confirmed no deletions or alterations in the Class 12 Biology textbook for 2026-27. Chapter 5 retains every numbered section, the lac operon diagram, the codon chart, the Hershey-Chase experiment, and the full DNA fingerprinting protocol.
What is the CBSE weightage of Molecular Basis of Inheritance in Class 12 Biology?
Molecular Basis of Inheritance typically carries 8 to 10 marks in the CBSE Class 12 Biology Board paper, usually split between one 3-mark short-answer on the genetic code or lac operon and one 5-mark long-answer on DNA replication or transcription.
Which sections of Chapter 5 are most important for CBSE Boards?
Sections 5.4 (Replication), 5.5 (Transcription), 5.6 (Genetic Code), 5.8 (Lac Operon), and 5.10 (DNA Fingerprinting) account for the bulk of CBSE Board questions. Within these, the diagrams in Figures 5.7, 5.10, and 5.13 are the most-repeated diagram-based questions.
Is the NCERT Class 12 Biology Chapter 5 PDF enough for NEET preparation?
The NCERT Chapter 5 PDF is the foundational text for NEET preparation and covers every concept tested in the exam. NEET aspirants should pair the PDF with the Collegedunia Notes and Formula Sheet for that chapter to lock in the diagrams and the codon table before timed practice.
Why is the lac operon repeated so often in NEET and CBSE?
The lac operon is the most diagram-rich and conceptually self-contained example of negative gene regulation in the Class 12 syllabus. It tests structural knowledge (six genetic elements), mechanistic knowledge (repressor-inducer logic), and historical knowledge (Jacob and Monod) within a single 5-mark question, which is why CBSE and NEET reuse it almost every year.
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