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 12 English Vistas Chapter 6: Memories of Childhood PDF Download & Complete Summary

Memories of Childhood is Chapter 6 in the Class 12 English Vistas textbook by NCERT. What makes this chapter special is that it’s not a single story—it’s made up of two autobiographical excerpts written by two women, Zitkala-Sa and Bama. Both narrate incidents from their early lives that reflect the discrimination they faced because of

Memories of Childhood is Chapter 6 in the Class 12 English Vistas textbook by NCERT. What makes this chapter special is that it’s not a single story—it’s made up of two autobiographical excerpts written by two women, Zitkala-Sa and Bama. Both narrate incidents from their early lives that reflect the discrimination they faced because of their identity. While Zitkala-Sa was a Native American who suffered cultural oppression, Bama grew up as a Dalit in South India, dealing with caste-based discrimination. These two stories are placed together in the chapter to show that such issues exist in many parts of the world.

I decided to write about this chapter because it’s different from the others in the book. It’s not fiction, but a real account of how young children feel when they are treated unfairly just because of their background. When I first read Bama’s story, I couldn’t stop thinking about how common such behaviour still is in many Indian towns. These stories make us more aware and sensitive. As students, we need to understand not just grammar and vocabulary but also social realities. This chapter is an important step towards building that understanding.

What is “Memories of Childhood” About?

This chapter includes two short autobiographical narratives that focus on childhood memories shaped by discrimination and injustice.

Part One: The Cutting of My Long Hair by Zitkala-Sa

This section is written by a Native American woman who was taken to a missionary school where they tried to make her behave like a “white” child. She describes how humiliating it was when her long hair was forcibly cut, which in her culture was a sign of defeat. She feels powerless, angry, and alien in a place that tries to erase her identity.

Part Two: We Too Are Human Beings by Bama

Bama’s story takes place in a village in Tamil Nadu. She is a young Dalit girl who notices how upper-caste people treat her community with disrespect. She sees a man carrying food for his master without touching it, just because of his caste. When she narrates this incident to her brother, he tells her about caste discrimination and advises her to study hard to earn respect and equality.

Main Characters:

Zitkala-Sa – A Native American girl forced to give up her culture at a white-run school
Bama – A young Dalit girl who slowly becomes aware of social injustice

Key Themes:

Discrimination based on race and caste
Childhood trauma and awareness
Loss of identity
Education as a tool for change

Why This Chapter Matters for Students

Real stories: It helps students connect emotionally to real-life problems faced by children
Relevant to society: Topics like caste and cultural identity are still important in today’s India
CBSE exam favourite: Frequently asked in long and value-based questions
Builds empathy: Helps students look beyond textbooks and understand people around them better
Teaches resilience: Both writers turned their pain into power through education and awareness