NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance PDF Notes Download

Chapter 5 of Class 12 Biology, Molecular Basis of Inheritance, covers how genetic material is structured, replicated, transcribed, and translated in living organisms. It talks about DNA, RNA, genetic code, gene expression, mutations, and the basics of biotechnology. This chapter helps students understand how traits are passed at the molecular level and how genes function

Chapter 5 of Class 12 Biology, Molecular Basis of Inheritance, covers how genetic material is structured, replicated, transcribed, and translated in living organisms. It talks about DNA, RNA, genetic code, gene expression, mutations, and the basics of biotechnology. This chapter helps students understand how traits are passed at the molecular level and how genes function inside our cells.

I am writing about this chapter because it plays a big role not only in CBSE board exams but also in competitive exams like NEET. The concepts in this chapter build a strong foundation for biotechnology, medicine, and genetic engineering. Many students feel overwhelmed by terms like replication, transcription, and translation. But once these are understood through simple examples and visuals, it becomes one of the most interesting parts of biology. That’s why I’ve broken down the important points and also added the official NCERT PDF download link so students can easily revise and practise from the original source.

Key Concepts in Molecular Basis of Inheritance

This chapter introduces the molecular structure of DNA and RNA and explains how genes control the functioning of cells.

DNA – The Genetic Material

DNA (Deoxyribonucleic Acid) was proven to be genetic material through Griffith’s transformation experiment and Avery, MacLeod and McCarty’s work
Hershey and Chase finally confirmed this using bacteriophages
Structure of DNA was explained by Watson and Crick – double helix with complementary base pairing (A-T and G-C)

DNA Replication

Takes place during the S-phase of the cell cycle
It is semi-conservative, meaning each new DNA has one old strand and one new
Enzymes involved:
- Helicase (unwinds DNA)
- DNA polymerase (adds nucleotides)
- Ligase (joins fragments on lagging strand)

RNA and Transcription

RNA (Ribonucleic Acid) types: mRNA, tRNA, rRNA
In transcription, DNA is used to make RNA
RNA polymerase is the key enzyme
Occurs in the nucleus in eukaryotes
Resulting mRNA carries code for protein synthesis

Genetic Code and Translation

Genetic code is made up of codons – triplets of nitrogen bases
64 codons exist; 61 code for amino acids, 3 are stop codons
Translation occurs in ribosomes where mRNA is read to form proteins
tRNA brings amino acids and matches them to the codon using its anticodon

Regulation of Gene Expression

In prokaryotes, gene expression is controlled by operons
Example: Lac operon in E. coli regulates lactose digestion
In eukaryotes, gene regulation is more complex and occurs at multiple levels

Human Genome Project (HGP)

Launched in 1990, completed in 2003
Aim: sequence all human genes and understand their function
Found around 3.2 billion base pairs and approx. 20,000-25,000 genes

DNA Fingerprinting

A technique used for identity verification, crime detection, paternity testing
Based on differences in VNTRs (Variable Number Tandem Repeats)
Developed by Alec Jeffreys

Download PDF – NCERT Class 12 Biology Chapter 5

Here’s how you can download the official NCERT Chapter 5 PDF for Class 12 Biology

NCERT Class 10 Math Chapter 14: प्रायिकता PDF Download

NCERT Class 10 Math Chapter 14 प्रायिकता (Probability) introduces students to the concept of chance and likelihood of events. In this chapter, students learn how to calculate the probability of simple events using the formula P(E) = Number of favourable outcomes ÷ Total number of outcomes. The chapter deals with real-life examples like tossing a

NCERT Class 10 Math Chapter 14 प्रायिकता (Probability) introduces students to the concept of chance and likelihood of events. In this chapter, students learn how to calculate the probability of simple events using the formula P(E) = Number of favourable outcomes ÷ Total number of outcomes. The chapter deals with real-life examples like tossing a coin, rolling a dice, or drawing cards, which makes the subject more interesting and practical. Since probability questions are common in board exams and are generally considered easy, this chapter is highly important for scoring well.

I am writing about this topic because probability is not only an important part of the Class 10 syllabus but also a concept that students will use in higher studies and real life. From predicting weather conditions to calculating risks in business, probability plays a key role. Many students initially find it confusing, but NCERT presents it in a simple and easy-to-understand manner. By practising from the NCERT book, students can build a strong foundation and develop confidence in solving probability problems. Having the PDF makes it easier for learners to access the chapter anytime, revise formulas, and attempt practice questions before exams.