CBSE Class 10 Heredity & Evolution Notes 2025 PDF

Heredity and Evolution is a really important topic and here in Class 10 Science Chapter 9 Notes, where you'll learn how traits are passed down from parents to their kids and how species change over time.

The chapter in Class 10 Science Syllabus covers important ideas like Mendel’s Laws of Inheritance, DNA, variations, natural selection, and speciation. Getting a good grip on these concepts will help you understand how characteristics are developed and how organisms evolve across generations. 

So, know more and level up your knowledge – because evolution never stops, and neither should your learning! 🌱

Heredity and Evolution Class 10 Notes Material PDF Download

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Important Notes from Heredity and Evolution Class 10

Heredity and Evolution explain how traits are passed from parents to their children and how species change over time. These ideas help us understand why living things look the way they do and how they adapt to their surroundings.

1. Heredity

Heredity is the process by which traits and characteristics are passed from parents to offspring through genes. It ensures that organisms of the same species show similarities but also have individual differences.

• Definition: The transmission of traits from parents to offspring.
• Genetics: The branch of biology that studies heredity and variations in living organisms.
• DNA (Deoxyribonucleic Acid): The genetic material that stores and transfers hereditary information across generations.
• Genes: Specific sequences of DNA responsible for inherited traits like eye color, height, and hair type.

Note: If both parents have curly hair, their child is more likely to inherit the same trait due to the presence of dominant genes for curly hair.

2. Mendel’s Laws of Inheritance

Gregor Mendel, known as the Father of Genetics, conducted experiments on pea plants to understand how traits are passed from one generation to another.

Mendel’s Three Laws:

• Law of Dominance:

In a pair of contrasting traits, one trait (dominant) is expressed while the other (recessive) is masked.

Example: If a tall plant (TT) is crossed with a short plant (tt), the offspring (Tt) will be tall because the T gene is dominant over t.

• Law of Segregation:

Each parent has two alleles for a trait, but only one is passed on to the offspring. These alleles separate during gamete formation.

Example: A hybrid tall plant (Tt) can produce gametes with either T or t allele.

• Law of Independent Assortment:

Genes for different traits are inherited independently, meaning the inheritance of one trait does not affect another.

Example: A pea plant's seed shape (round or wrinkled) is inherited independently of its flower color (purple or white).

Note: Mendel’s experiments helped explain how dominant and recessive traits work and how variations occur in offspring.

3. Variations and Their Importance

Variation refers to the differences between individuals of the same species. These variations are crucial for survival and evolution.

• Causes of Variation:

Mutations: Sudden changes in DNA that can introduce new traits.

Genetic Recombination: Mixing of genes during reproduction leads to unique combinations.

Environmental Factors: Climate, diet, and habitat can influence traits.

• Why are Variations Important?

Helps in Adaptation: Organisms with beneficial traits survive in changing environments.

Leads to Evolution: Over time, variations accumulate, leading to the development of new species.

Note: The long neck of giraffes evolved over generations because it helped them reach leaves on tall trees, giving them a survival advantage.

4. Evolution and Natural Selection

Evolution is the gradual change in the traits of a species over generations. It is driven by natural selection, genetic mutations, and environmental factors.

• Natural Selection (Darwin’s Theory):

Organisms with favorable traits survive and reproduce, while those with weaker traits die out.

Example: Peppered moths in industrial England – before pollution, white moths were common, but after pollution dark moths survived better as they were camouflaged against soot-covered trees.

• Speciation:

Over time, variations lead to the formation of new species when populations become isolated due to factors like geographical barriers.

Example: Darwin’s Finches – Birds on the Galápagos Islands evolved different beak shapes based on their food sources.

• Fossil Evidence:

Fossils are the preserved remains of ancient organisms, providing proof of evolution.

Example: Archaeopteryx is considered a transitional fossil showing a link between reptiles and birds.

Note: Evolution is a slow and continuous process that explains the diversity of life on Earth.

5. Sex Determination in Humans

Sex determination is the biological process that decides whether an offspring will be male or female, controlled by chromosomes.

Chromosome Pairs:

• Females have XX chromosomes.
• Males have XY chromosomes.

Who Determines the Baby’s Gender?

1. The mother always provides an X chromosome (as she has XX).
2. The father can contribute either X or Y (since he has XY).
3. If the father passes an X, the baby will be female (XX).
4. If the father passes a Y, the baby will be male (XY).

Note: The father’s sperm determines the sex of the baby since he contributes the deciding X or Y chromosome.

Important Questions from Ch 9 Heredity and Evolution Class 10

CBSE Class 10 Science Chapter 9 covers the process of evolution and the mechanisms that drive changes in species over time. Here are some important questions that will help you understand the key concepts in this chapter:

1. Very Short Answer Questions (1 Mark Each)

Q1. What is heredity?
Ans: Heredity is the transmission of traits from parents to offspring through genes.

Q2. What is the full form of DNA?
Ans: DNA stands for Deoxyribonucleic Acid.

Q3. Name the scientist who proposed the theory of natural selection.
Ans: Charles Darwin proposed the theory of natural selection.

Q4. What is a gene?
Ans: A gene is a segment of DNA that controls a specific trait in an organism.

Q5. What are fossils?
Ans: Fossils are the preserved remains or impressions of ancient organisms found in rocks.

2. Short Answer Questions (2-3 Marks Each)

Q6. What is meant by variation in organisms? Why is it important?
Ans: Variation refers to the differences in traits among individuals of the same species. It is important because it helps species adapt to changing environments and contributes to evolution.

Q7. What do you understand by the term “dominant and recessive traits”?
Ans:

• Dominant Trait: A trait that appears in the offspring even if only one parent passes it on. Example: Tallness in pea plants (T).
• Recessive Trait: A trait that appears only when both parents pass it on. Example: Shortness in pea plants (t).

Q8. What is a monohybrid cross? Give an example.
Ans: A monohybrid cross is a genetic cross between parents that differ in only one trait.
Example: When a tall pea plant (TT) is crossed with a short pea plant (tt), the first generation (F1) will have all tall (Tt) plants, as tallness is dominant.

Q9. How does the process of speciation occur?
Ans: Speciation occurs due to:

1. Genetic variations – Differences in traits among individuals.
2. Natural selection – Survival of the fittest organisms.
3. Geographical isolation – When a group of organisms is separated from others due to a physical barrier (e.g., mountains, rivers), they evolve into a new species over time.

Q10. What is the role of fossils in studying evolution?
Ans: Fossils provide evidence of how organisms have changed over time, showing links between ancient and modern species. Example: Archaeopteryx, which has features of both birds and reptiles, proving the evolution of birds from reptiles.

3. Long Answer Questions (4-5 Marks Each)

Q11. Explain Mendel’s experiment on pea plants. What were his conclusions?
Ans:
Mendel conducted experiments on pea plants and observed how traits are inherited.

• He crossed tall (TT) plants with short (tt) plants.
• In the first generation (F1), all plants were tall (Tt).
• In the second generation (F2), he got 3 tall plants and 1 short plant (3:1 ratio).

Conclusions:

1. Traits are controlled by genes.
2. Some traits are dominant, while others are recessive.
3. Traits are passed down from parents to offspring without blending.

Q12. Explain the mechanism of sex determination in humans.
Ans:

• Humans have 23 pairs of chromosomes. The last pair (XX or XY) determines the sex.
• Males have XY chromosomes, while females have XX chromosomes.
• During fertilization:

1. If a sperm carrying X chromosome fertilizes the egg (X), the baby will be a girl (XX).
2. If a sperm carrying Y chromosome fertilizes the egg (X), the baby will be a boy (XY).

• Thus, the father’s sperm determines the sex of the child.

Q13. What is natural selection? Explain with an example.
Ans:
Natural selection is the process by which individuals with favorable traits survive and reproduce.

Example:

• Peppered Moths during the Industrial Revolution.
• Before industrialization, white moths were common as they blended with trees.
• After pollution darkened trees, black moths survived better as they were camouflaged.
• Over time, the black moth population increased, showing how natural selection works.

4. Numericals and Practice Problems

Q14. In a cross between a pure tall plant (TT) and a pure short plant (tt), what will be the genotype and phenotype of the F1 and F2 generations?

Solution:

• F1 Generation: TT × tt → All Tt (Tall plants)
• F2 Generation: Tt × Tt → 3 Tall (TT, Tt, Tt) : 1 Short (tt)

Q15. If a child has blood group O, what are the possible blood groups of the parents?

Solution:

Blood group O means the child has OO genotype.

Parents can have the following possible genotypes:

• A (AO) × O (OO)
• B (BO) × O (OO)
• O (OO) × O (OO)
• A (AO) × B (BO)

Common Mistakes to Avoid

🚫 Confusing dominant and recessive traits – Remember, dominant traits mask recessive ones.

🚫 Forgetting to label Punnett squares correctly – Always label parental genotypes properly.

🚫 Misunderstanding natural selection – It does not create new traits but selects beneficial ones.

🚫 Ignoring sex determination concepts – It is determined by the father’s chromosome (X or Y).

🚫 Not revising Mendel’s ratios – 3:1 (monohybrid cross) and 9:3:3:1 (dihybrid cross).

Creative Ways to Make Notes for Heredity and Evolution Ch 9 Class 10

Instead of rote memorization, try these engaging methods to create notes that help in better understanding and retention:

• Draw Family Trees – Use Punnett squares to visualize inheritance patterns in Mendel’s experiments. This will help you understand how traits passed from one generation to another.
• Use Mnemonics – Remember key Mendelian principles with short tricks like “LID” (Law of Dominance, Independent Assortment, and Segregation).
• Make Flashcards – Write important terms like alleles, genotype, phenotype, dominant, recessive on one side and their definitions on the other for quick revision.
• Create Evolution Timelines – Sketch a timeline of evolution showing major changes in species over time with examples like Archaeopteryx (link between reptiles and birds).
• Color-Coding Notes – Highlight dominant traits in one color and recessive traits in another to easily differentiate between them.
• Storytelling Method – Convert complex topics like natural selection into short stories or real-life examples to make them more relatable.
• Use Mind Maps – Connect concepts like heredity, variation, evolution, and speciation visually to see how they are interrelated.

How Can Notes Help?

• Quick Revision – Well-structured notes make last-minute preparation easier, saving time before exams.
• Better Retention – Writing concepts in your own words helps you understand and remember them better.
• Improves Answer Writing – Organized notes help in framing clear and concise answers, just like CBSE expects.
• Easy Diagram Practice – Regularly drawing and labeling key diagrams (like Punnett squares, evolution charts, and family trees) helps in better recall during exams.
• Useful for Competitive Exams – A strong grasp of hereditary concepts is essential for exams like NEET, NTSE, and other Olympiads, making these notes a long-term asset.

Heredity and Evolution explains how traits are passed on and how species change over time. By understanding Mendel’s experiments, natural selection, and variation, you can answer CBSE board exam questions with confidence. Make your own creative notes, avoid common mistakes, and revise diagrams for better retention! Happy Learning!

Frequently Asked Questions

What is heredity and how does it work?
Heredity is the process by which traits are passed from parents to offspring through genes. It explains how physical characteristics like eye color or height are inherited.

What are Mendel’s Laws of Inheritance?
Mendel's Laws of Inheritance include the Law of Dominance, the Law of Segregation, and the Law of Independent Assortment, which describe how traits are inherited from one generation to the next.

What is the role of DNA in heredity?
DNA carries genetic information that is passed down from parents to offspring. It contains the instructions for growth, development, and functioning of all living organisms.

What is natural selection and how does it relate to evolution?
Natural selection is the process where organisms better adapted to their environment tend to survive and reproduce, leading to the gradual evolution of species over time.

How do variations contribute to the process of evolution?
Variations are differences in traits among individuals of a species. These differences can lead to adaptations that increase survival chances, driving the process of evolution over generations.