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NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation PDF Notes Download

Chapter 4 of Class 12 Biology, Principles of Inheritance and Variation, explains how traits are passed from one generation to another. It talks about Mendel’s laws of inheritance, genetic crosses, linkage, recombination, sex determination, mutation, and genetic disorders. These concepts form the base of classical genetics and help us understand how genes influence physical traits

NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation PDF

Chapter 4 of Class 12 Biology, Principles of Inheritance and Variation, explains how traits are passed from one generation to another. It talks about Mendel’s laws of inheritance, genetic crosses, linkage, recombination, sex determination, mutation, and genetic disorders. These concepts form the base of classical genetics and help us understand how genes influence physical traits and diseases.

I’m writing about this chapter because it is one of the most frequently asked sections in both CBSE board exams and NEET. Understanding inheritance patterns and variations is not just important for scoring marks but also for understanding how living organisms evolve and why genetic differences exist. Most students find this chapter slightly tricky in the beginning due to the number of terms and genetic crosses, but once understood clearly, it becomes one of the most scoring chapters. I have tried to make the explanations simple and relatable. Also, I have shared the link to download the NCERT PDF for this chapter so that you can revise the concepts at your convenience.

Mendel’s Experiments and Laws of Inheritance

Gregor Mendel, known as the father of genetics, performed hybridisation experiments on pea plants. His work laid the foundation of classical genetics.

Key Terms

  • Gene: Unit of inheritance
  • Allele: Different forms of a gene
  • Homozygous: Same alleles (TT or tt)
  • Heterozygous: Different alleles (Tt)
  • Phenotype: Physical appearance
  • Genotype: Genetic makeup

Mendel’s Laws

  1. Law of Dominance: In a heterozygous pair, the dominant allele expresses itself
  2. Law of Segregation: Alleles separate during gamete formation
  3. Law of Independent Assortment: Traits assort independently during inheritance

Mendel’s Crosses

  • Monohybrid Cross: Involves one trait (e.g. tall vs. dwarf)
    • F1 Generation: All tall (Tt)
    • F2 Generation Ratio: 3 Tall : 1 Dwarf (Phenotypic), 1:2:1 (Genotypic)
  • Dihybrid Cross: Involves two traits (e.g. seed shape and colour)
    • F2 Generation Phenotypic Ratio: 9:3:3:1

Quick Summary Table

ConceptExample/Details
Mendel’s LawsDominance, Segregation, Independent Assortment
Incomplete DominancePink flowers in Mirabilis jalapa
CodominanceAB blood group
Multiple AllelesABO blood system
Sex DeterminationXX-XY system in humans
MutationSickle cell anaemia, Down’s syndrome

Download PDF – NCERT Class 12 Biology Chapter 4

To download the official PDF of this chapter for free:

NCERT Class 12 Biology Chapter 4

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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

NCERT Class 12 English Vistas Chapter 6: Memories of Childhood

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

Download PDF

You can download the official NCERT Class 12 English Vistas Chapter 6 PDF from here:

NCERT Class 12 English Vistas Chapter 6: Memories of Childhood

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