Molecular Basis of Inheritance Notes, Class 12 Biology Notes, DNA Replication Notes, Transcription and Translation NEET, Lac Operon Notes, Human Genome Project Notes, DNA Fingerprinting Notes, Molecular Basis of Inheritance PYQ, NEET 2026 Biology Notes.
The chapter Molecular Basis of Inheritance is one of the highest-weightage chapters in NEET Biology. Questions are frequently asked from DNA structure, replication, transcription, translation, operon concept, genetic code, and Human Genome Project.
Introduction
Inheritance occurs through genetic material called DNA (Deoxyribonucleic Acid).
DNA stores, transmits, and expresses genetic information.
Search for Genetic Material
Griffith's Experiment (1928)
Organism:
Streptococcus pneumoniae
Observation
R strain → Non-virulent
S strain → Virulent
Heat-killed S strain + Live R strain → Mouse died
Conclusion
Some transforming principle transferred genetic information.
Avery, MacLeod and McCarty Experiment
Conclusion
DNA is the genetic material.
Hershey and Chase Experiment
Organism:
Bacteriophage
Conclusion
DNA enters bacterial cells and acts as genetic material.
NCERT Point
DNA is the genetic material in most organisms.
Structure of DNA
Proposed by:
James Watson
Francis Crick
Based on X-ray diffraction studies of:
Rosalind Franklin
Features of DNA
Double helix structure
Two antiparallel strands
Sugar-phosphate backbone
Nitrogenous bases
Base Pairing
A ↔ T
G ↔ C
Chargaff's Rule
A = T
G = C
DNA Packaging
Human DNA length:
Approximately 2.2 meters per cell
Packaging protein:
Histones
Nucleosome
DNA wrapped around histone octamer.
NCERT Point
Nucleosome is the repeating unit of chromatin.
DNA Replication
DNA replication is semiconservative.
Confirmed by:
Matthew Meselson
Franklin Stahl
Steps
Unwinding
Complementary base pairing
Formation of daughter strands
Important Enzyme
DNA Polymerase
NCERT Point
Replication occurs in 5' → 3' direction.
Transcription
Process of formation of RNA from DNA template.
Enzyme
RNA Polymerase
Types of RNA
mRNA
tRNA
rRNA
NCERT Point
Only one strand acts as template strand.
Genetic Code
Properties:
Triplet Code
One amino acid = Three nucleotides
Degenerate
Multiple codons code for same amino acid.
Universal
Same in almost all organisms.
Start Codon
AUG
Stop Codons
UAA
UAG
UGA
Translation
Process of protein synthesis from mRNA.
Site
Ribosomes
Main Steps
Activation of amino acids
Initiation
Elongation
Termination
NCERT Point
AUG codes for Methionine.
Lac Operon
Proposed by:
François Jacob
Jacques Monod
Components
Regulatory gene
Promoter
Operator
Structural genes
Inducer
Lactose
NCERT Point
Lac operon is an inducible operon.
Human Genome Project (HGP)
Objectives
Identify all genes
Determine DNA sequences
Store information
Facts
Human genome contains approximately 3.2 billion base pairs.
Around 20,000–25,000 genes.
DNA Fingerprinting
Developed by:
Alec Jeffreys
Principle
Based on polymorphism in DNA sequences.
Applications
Forensic science
Paternity testing
Criminal identification
Important Scientists for NEET
Scientist
Contribution
Griffith
Transformation
Avery, MacLeod & McCarty
DNA as genetic material
Hershey & Chase
DNA proof
Watson & Crick
DNA structure
Meselson & Stahl
Semiconservative replication
Jacob & Monod
Lac Operon
Alec Jeffreys
DNA Fingerprinting
Most Important NCERT Lines
✔ DNA is the genetic material in most organisms.
✔ DNA replication is semiconservative.
✔ AUG is the initiation codon.
✔ UAA, UAG and UGA are stop codons.
✔ Genetic code is universal and degenerate.
✔ Nucleosome is the repeating unit of chromatin.
✔ Lac operon is inducible.
✔ DNA fingerprinting is based on polymorphism.
NEET PYQ Practice Questions
Q1. DNA double helix model was proposed by:
A. Griffith
B. Watson and Crick
C. Hershey and Chase
D. Jacob and Monod
✅ Answer: B
Q2. Start codon is:
A. UAA
B. AUG
C. UGA
D. UAG
✅ Answer: B
Q3. DNA replication is:
A. Conservative
B. Dispersive
C. Semiconservative
D. Random
✅ Answer: C
Q4. DNA fingerprinting was developed by:
A. Watson
B. Crick
C. Alec Jeffreys
D. Griffith
✅ Answer: C
Q5. Inducer in lac operon is:
A. Glucose
B. Lactose
C. DNA
D. RNA
✅ Answer: B
Last-Minute NEET Revision
Focus on:
DNA structure
Chargaff's rule
DNA replication
Transcription
Translation
Genetic code
Lac operon
Human Genome Project
DNA fingerprinting
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