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I. Chapter Summary

The chapter Heredity explains how traits and characteristics are passed from one generation to the next through genes. It introduces key concepts like inheritance, variation, and genetic traits, and discusses Mendel’s experiments on pea plants. The chapter also distinguishes between dominant and recessive traits, and introduces the monohybrid cross. Students learn about sex determination in humans, and how variations arise and help in the evolution of species.

II. Key Concepts Covered

Concept	Explanation
Heredity	Transmission of genetic traits from parents to offspring.
Traits	Characteristics or features that are inherited (e.g., eye color, height).
Gene	A unit of inheritance that determines a trait.
Allele	Different forms of the same gene (dominant/recessive).
Mendel’s Experiment	Conducted with pea plants; introduced concepts of dominant/recessive traits, monohybrid cross, and inheritance patterns.
Monohybrid Cross	A cross involving a single pair of contrasting traits (e.g., tall × dwarf plants).
Phenotype & Genotype	Phenotype: observable traits; Genotype: genetic makeup.
Sex Determination in Humans	XX (female), XY (male); determined by the type of sperm that fertilizes the ovum.
Variation	Differences in traits among individuals; may arise due to errors in DNA copying or sexual reproduction.

III. Important Questions

(A) Multiple Choice Questions (1 Mark)

1. Which of the following is a recessive trait in pea plant according to Mendel?
   a) Tall stem
   b) Yellow seed
   c) Round seed
   d) Dwarf stem ✅ (PYQ 2020)
2. A male has which combination of sex chromosomes?
   a) XX
   b) XY ✅ (PYQ 2021)
   c) YY
   d) XO
3. The visible trait in an organism is called:
   a) Genotype
   b) Phenotype ✅
   c) Chromotype
   d) Genome
4. Which pair of chromosomes is responsible for determining the sex of a child?
   a) 21st pair
   b) 22nd pair
   c) 23rd pair ✅
   d) 24th pair

(B) Short Answer Questions (2/3 Marks)

1. State the basic features of the mechanism of inheritance.
2. What is meant by variation in organisms? How is it useful in evolution?
3. What is the difference between dominant and recessive traits? Explain with an example.
4. State Mendel’s law of segregation. (PYQ 2019)

(C) Long Answer Questions (5 Marks)

1. Explain Mendel’s monohybrid cross with a diagram. What conclusion did Mendel draw from it? (PYQ 2020)
2. How is sex determined in human beings? Explain with the help of a diagram.
3. Differentiate between inherited traits and acquired traits. Why are acquired traits not passed on to the next generation?
4. Explain how traits are inherited through sexual reproduction using Mendel’s experiments.

(D) HOTS (Higher Order Thinking Skills)

1. Why does a child always resemble the biological parents but not exactly look like either of them?
2. In a cross between tall (TT) and dwarf (tt) plants, all offspring are tall. Explain why. What will be the genotype and phenotype in F₂ generation?

IV. Key Formulas/Concepts

Term	Definition/Example
Phenotype	The visible trait (e.g., tall or dwarf plant).
Genotype	The genetic makeup (e.g., TT, Tt, or tt).
Homozygous	Having two identical alleles (e.g., TT or tt).
Heterozygous	Having two different alleles (e.g., Tt).
Monohybrid Cross Ratio
– Genotypic ratio: 1:2:1
– Phenotypic ratio: 3:1

V. Deleted Portions (CBSE 2025–2026)

No portions have been deleted from this chapter as per the rationalized NCERT textbooks.

VI. Chapter-Wise Marks Bifurcation (Estimated – CBSE 2025–2026)

Unit/Chapter	Estimated Marks	Type of Questions Typically Asked
Chapter 8: Heredity	4–6 Marks	1 Long Answer, 1–2 Short Answers, 1–2 MCQs

VII. Previous Year Questions (PYQs)

Year	Marks	Question
2021	1	A male has which combination of sex chromosomes? (XY)
2020	5	Explain Mendel’s monohybrid cross with suitable diagram.
2019	2	State Mendel’s law of segregation.
2018	3	What is the difference between acquired and inherited traits?

VIII. Real-World Application Examples to Connect with Topics

Concept	Real-World Connection
Sex Determination	Genetic counseling, IVF technology, legal issues related to sex selection.
Variation and Evolution	Breeding programs in agriculture and animals for desired traits.
Traits and Inheritance	Studying hereditary diseases like hemophilia, thalassemia.
Mendel’s Principles	Used in modern genetics and biotechnology research.

IX. Student Tips & Strategies for Success

Time Management

• Spend 15 minutes daily revising genetic terms and laws.
• Use Punnett squares for better understanding of crosses.

Exam Preparation

• Practice monohybrid cross diagrams thoroughly.
• Prepare tables comparing dominant vs recessive traits, genotype vs phenotype.
• Focus on NCERT questions + PYQs.

Stress Management

• Use visual tools like family tree charts and gene diagrams.
• Avoid memorization; understand concept flow and logic.

X. Career Guidance & Exploration (Class-Specific)

For Classes 9–10

Academic Streams

• Science: Genetics, Molecular Biology, Medicine
• Commerce: Biotechnology Business, Health Management
• Arts: Bioethics, Science Communication

Career Paths

• Geneticist, Biotechnologist, Genetic Counselor, Forensic Analyst, Researcher

Foundational Exams

• NTSE, NSO, Junior Science Olympiad, KVPY (Class 11+)

XI. Important Notes

• Always check https://ncert.nic.in and https://cbseacademic.nic.in for syllabus updates.
• Focus on understanding genetic patterns, diagrams, and ratios.
• Practice labeled Punnett square crosses for clarity.
• Use keywords such as dominant, recessive, zygote, homozygous, heterozygous in answers.