CBSE Class 12 Biology Question Bank: Molecular Basis of Inheritance DNA Replication 2026
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The academic year 2026 marks a significant shift in the CBSE Class 12 Biology examination pattern, with a 50% increase in competency-based questions. Within the unit of Genetics and Evolution—which carries a staggering 20 marks—the chapter "Molecular Basis of Inheritance" remains the crown jewel. Specifically, DNA Replication is a high-yield topic that consistently appears in both subjective board papers and competitive medical entrance exams like NEET and FMGE.
This comprehensive guide serves as your ultimate CBSE Class 12 Biology Question Bank, specifically designed to help you navigate the complexities of the Molecular Basis of Inheritance and secure a perfect score in 2026.
The Central Dogma and the Core of DNA Replication
Before diving into the question bank, it is vital to understand the "why" behind the process. In 1953, Watson and Crick didn't just propose the double helix; they famously noted that the specific pairing they suggested immediately hinted at a possible copying mechanism for genetic material.
DNA Replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. In eukaryotes, this occurs during the S-phase of the cell cycle. For medical aspirants, understanding this is crucial because errors in this phase are the root cause of many oncogenic (cancer-causing) mutations.
CBSE Important Formulas and Quantitative Concepts
While Biology is often perceived as purely theoretical, the Molecular Basis of Inheritance requires a firm grasp of biochemical ratios and molecular counts. Based on recent board trends, ensure you know the following:
Chargaff’s Rule: Used to calculate base pair percentages.
DNA Length Calculation: Calculating the length based on total base pairs (4.6 \times 10^6 bp for E. coli and 3.3 \times 10^9 bp for human haploid content).
Nucleosome Calculations: Determining the number of nucleosomes in a given DNA length.
Replication Time Rate: Calculating the rate of polymerization (approximately 2000 bp per second in E. coli).
CBSE Class 12 Biology Question Bank: DNA Replication 2026
To rank high in your 2026 boards, you must practice questions that test both memory and application. Below is a curated list of high-probability questions categorized by marks.
Very Short Answer Questions (1 Mark)
Name the enzyme that acts as the primary catalyst for DNA-dependent DNA polymerization.
Define the Origin of Replication (ori) and its significance in vector selection.
Why is DNA replication called semiconservative?
In which direction does DNA Polymerase catalyze the polymerization of deoxynucleotides?
Short Answer Questions (2 - 3 Marks)
Explain the role of the following enzymes in DNA Replication:
Helicase
DNA Ligase
Primase
Differentiate between the Leading Strand and the Lagging Strand.
What are Okazaki fragments, and why are they formed only on one strand?
Medical Relevance: How does the proofreading activity of DNA Polymerase prevent genetic disorders?
Long Answer Questions (5 Marks)
The Meselson and Stahl Experiment: Provide a detailed account of how they proved the semiconservative nature of replication using ^{15}N and ^{14}N isotopes of NH_4Cl. Include the ratios of hybrid DNA after 20 and 40 minutes.
The Machinery of Replication: Describe the entire process of DNA replication with a neatly labeled diagram of the Replication Fork.
Medical Perspectives: Linking Boards to NEET & FMGE 2026
For students aiming for medical excellence, DNA Replication isn't just a chapter; it’s a foundation for Pharmacology and Pathology.
FMGE 2026 Focus: In the Foreign Medical Graduate Examination, questions often link DNA replication enzymes to antibiotic mechanisms (e.g., how Quinolones inhibit Topoisomerase).
NEET 2026 Trends: Expect more assertion-reasoning questions regarding the energetics of replication (the role of Deoxyribonucleoside triphosphates acting as both substrate and energy source).
Official Resources and Practice Links
To ensure you are practicing the most authentic material, always refer to the official portals:
Conclusion
Success in the CBSE Class 12 Biology exam requires a blend of NCERT depth and consistent practice of previous year questions. By focusing on the enzymatic machinery and the experimental proofs of DNA replication, you prepare yourself not just for the boards, but for a future in the medical sciences.
FAQ: CBSE Class 12 Biology Question Bank
Q1: Which is the most important enzyme in the CBSE Class 12 Biology Question Bank for this chapter?
A: DNA-dependent DNA Polymerase is the most frequently asked enzyme. However, for 2026, questions on DNA Ligase and Topoisomerase are trending due to their roles in biotechnology and medicine.
Q2: Are diagrams mandatory for DNA Replication questions?
A: Yes. According to the 2026 marking scheme, a 5-mark question on the replication fork usually carries 2 marks specifically for a correctly labeled diagram.
Q3: How many marks does the "Molecular Basis of Inheritance" carry?
A: This chapter typically carries 8 to 10 marks within the 20-mark Genetics unit, making it the highest-weightage single chapter in the syllabus.
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