🧬 Class 10 Biology — Heredity and Evolution Complete Detailed Notes
CBSE Board 2026 | NCERT Based | PYQs | Important Questions | Tricks | Diagrams | Board Answers
📖 Introduction
Living organisms produce offspring that resemble their parents. This happens because traits are passed from one generation to another. This transmission of traits is called heredity.
At the same time, small differences also appear among organisms. These differences are called variations. Variations accumulate over generations and lead to evolution.
🌟 Important Definitions
| Term | Definition |
|---|---|
| Heredity | Transmission of traits from parents to offspring |
| Variation | Differences among individuals of same species |
| Evolution | Gradual change in organisms over generations |
| Trait | A characteristic feature |
| Gene | Functional unit of heredity |
| Chromosome | Thread-like structure carrying genes |
🌟 Why Are Variations Important?
Variations are important because they:
- Help organisms adapt to changing environment
- Increase chances of survival
- Form basis of evolution
🌟 Types of Variations
| Type | Example |
|---|---|
| Useful variation | Long neck in giraffe |
| Harmful variation | Genetic disease |
| Neutral variation | Different eye colour |
🧬 Heredity
Heredity is the process by which characteristics are transferred from parents to offspring through genes.
🌟 Examples of Hereditary Traits
- Eye colour
- Hair colour
- Blood group
- Height
🌟 Acquired Traits
Traits developed during an individual’s lifetime due to environmental effects or habits are called acquired traits.
Examples:
- Bodybuilding muscles
- Pierced ears
- Learning skills
Acquired traits are not inherited because they do not affect genes.
🌟 Genes
Genes are small segments of DNA present on chromosomes that control traits.
🌟 DNA
Full Form:
Deoxyribonucleic Acid
DNA contains hereditary information.
🌟 Chromosomes
Chromosomes are thread-like structures present in nucleus carrying genes.
Humans have:
- 46 chromosomes
- 23 pairs of chromosomes
🧬 Gregor Mendel and His Experiments
Gregor Mendel is known as the Father of Genetics.
He performed experiments on pea plants to study inheritance.
🌟 Why Did Mendel Choose Pea Plants?
Reasons:
- Short life cycle
- Easily visible contrasting traits
- Naturally self-pollinating
- Easy to grow
🌟 Contrasting Traits Studied by Mendel
| Character | Dominant Trait | Recessive Trait |
|---|---|---|
| Height | Tall | Dwarf |
| Seed shape | Round | Wrinkled |
| Seed colour | Yellow | Green |
| Flower colour | Violet | White |
🌟 Important Terms
| Term | Meaning |
|---|---|
| Dominant trait | Trait expressed in F₁ generation |
| Recessive trait | Trait hidden in F₁ generation |
| Genotype | Genetic makeup |
| Phenotype | Physical appearance |
🧬 Monohybrid Cross ⭐ Very Important
A cross involving only one pair of contrasting characters is called monohybrid cross.
Example:
Tall plant × Dwarf plant
🌟 Monohybrid Cross Diagram
🌟 Mendel’s Experiment
Parent Generation:
Tall plant (TT) × Dwarf plant (tt)
🌟 F₁ Generation
All offspring were tall (Tt).
This showed that:
- Tallness is dominant
- Dwarfness is recessive
🌟 F₂ Generation
When F₁ plants self-pollinated:
Ratio obtained:
3 Tall : 1 Dwarf
🌟 Law of Dominance
In a pair of contrasting traits, only one trait expresses itself in F₁ generation. This is called dominant trait.
🌟 Law of Segregation
Traits separate during formation of gametes and reunite during fertilization.
🧬 Dihybrid Cross
Cross involving two pairs of contrasting characters.
Example:
Round yellow seeds × wrinkled green seeds
🌟 Dihybrid Ratio
9 : 3 : 3 : 1
🌟 Sex Determination in Humans ⭐
Sex determination is the process by which sex of a child is determined.
🌟 Human Chromosomes
Humans have:
- 22 pairs of autosomes
- 1 pair of sex chromosomes
🌟 Sex Chromosomes
| Gender | Chromosomes |
|---|---|
| Male | XY |
| Female | XX |
🌟 Sex Determination Diagram
🌟 How Is Sex Determined?
Mother always contributes X chromosome.
Father contributes:
- X chromosome → Girl (XX)
- Y chromosome → Boy (XY)
Therefore, the father determines the sex of the child.
🌟 Important NCERT Point ⭐
The probability of getting a boy or girl is 50%.
🌍 Evolution
Evolution means gradual change in organisms over millions of years.
🌟 Causes of Evolution
- Variations
- Natural selection
- Genetic drift
- Geographical isolation
🌟 Charles Darwin and Natural Selection
Charles Darwin proposed the theory of natural selection.
🌟 Natural Selection
Organisms with favourable variations survive and reproduce better.
This is called “Survival of the Fittest”.
🌟 Speciation
Formation of new species from existing species.
🌟 Factors Leading to Speciation
1. Geographical Isolation
Physical barriers separate populations.
Examples:
- Mountains
- Rivers
- Seas
2. Genetic Drift
Random changes in gene frequency.
3. Natural Selection
Environment selects organisms with useful variations.
🌟 Evolution and Classification
Organisms with similar characteristics are grouped together because they share common ancestry.
🌟 Homologous Organs ⭐
Organs having:
- Same basic structure
- Same origin
- Different functions
Examples:
- Human arm
- Whale fin
- Bat wing
These provide evidence for divergent evolution.
🌟 Homologous Organs Diagram
🌟 Analogous Organs ⭐
Organs having:
- Different structure
- Different origin
- Same function
Example:
- Wings of bird
- Wings of insect
These provide evidence for convergent evolution.
🌟 Analogous Organs Diagram
🌟 Fossils ⭐ Very Important
Fossils are preserved remains or traces of ancient organisms.
🌟 Importance of Fossils
- Provide evidence of evolution
- Help determine age of organisms
- Show extinct species
- Help study evolutionary history
🌟 Fossil Diagram
🌟 Evolution by Stages
Complex organs evolved gradually over time.
Example:
Evolution of eye
🌟 Human Evolution
Modern humans evolved from ape-like ancestors over millions of years.
🔥 Important Differences
Acquired Trait vs Inherited Trait
| Acquired Trait | Inherited Trait |
|---|---|
| Develops during life | Present from birth |
| Not inherited | Inherited |
| Example: Muscles | Example: Eye colour |
Homologous vs Analogous Organs
| Homologous Organs | Analogous Organs |
|---|---|
| Same origin | Different origin |
| Different functions | Same functions |
| Divergent evolution | Convergent evolution |
Dominant Trait vs Recessive Trait
| Dominant Trait | Recessive Trait |
|---|---|
| Expressed in F₁ generation | Hidden in F₁ generation |
| Represented by capital letter | Represented by small letter |
🎯 Most Important Board Questions with Answers
Q1. Why is Mendel called the Father of Genetics?
Answer:
Gregor Mendel performed experiments on pea plants and explained the basic laws of inheritance. Therefore, he is called the Father of Genetics.
Q2. What are homologous organs? Give examples.
Answer:
Homologous organs are organs having similar basic structure and origin but different functions.
Examples:
Human arm, whale fin and bat wing.
Q3. Why are variations important?
Answer:
Variations help organisms adapt to changing environmental conditions and increase chances of survival.
Q4. Explain sex determination in humans.
Answer:
Humans have XX chromosomes in females and XY chromosomes in males.
Mother always contributes X chromosome while father contributes either X or Y chromosome.
- XX → Female child
- XY → Male child
Therefore, father determines the sex of the child.
Q5. What are fossils? Mention their importance.
Answer:
Fossils are preserved remains or impressions of ancient organisms.
Importance:
- Provide evidence of evolution
- Help study extinct organisms
- Show evolutionary relationships
🔥 Important NCERT Points
- Acquired traits are not inherited.
- Variations are important for survival.
- Fossils provide evidence for evolution.
- Sex determination depends on father.
- Homologous organs indicate common ancestry.
🧠 Super Tricks
Genetics Terms:
“GCD”
- Gene
- Chromosome
- DNA
Mendel Ratios:
- Monohybrid → 3:1
- Dihybrid → 9:3:3:1
Human Chromosomes:
“22 + 1”
- 22 pairs autosomes
- 1 pair sex chromosomes
✍️ Most Important Diagrams for Boards
- Monohybrid cross
- Sex determination
- Homologous organs
- Analogous organs
- Fossils
🎯 Expected Questions for CBSE Board 2026
- Explain Mendel’s monohybrid cross.
- What are homologous organs?
- Explain sex determination in humans.
- Differentiate inherited and acquired traits.
- What are fossils?
- Explain natural selection.
- Why are variations important?
- Differentiate homologous and analogous organs.
Evolution (Class 10 Science) – 20 Important MCQs
1. Evolution means: A) Growth of an organism
B) Gradual change in living organisms over generations
C) Reproduction
D) Respiration
✅ Answer: B
2. The theory of Natural Selection was proposed by: A) Lamarck
B) Mendel
C) Darwin
D) Aristotle
✅ Answer: C
3. Evolution is supported by: A) Fossils
B) Comparative anatomy
C) Embryology
D) All of these
✅ Answer: D
4. Fossils are: A) Living organisms
B) Preserved remains of ancient organisms
C) Rocks only
D) Minerals only
✅ Answer: B
5. The age of fossils can be determined by: A) Carbon dating
B) Litmus test
C) Titration
D) Distillation
✅ Answer: A
6. Homologous organs indicate: A) Common ancestry
B) Different ancestry
C) No relation
D) Extinction
✅ Answer: A
7. Forelimbs of humans, whales and bats are examples of: A) Analogous organs
B) Homologous organs
C) Vestigial organs
D) Fossils
✅ Answer: B
8. Wings of birds and insects are: A) Homologous organs
B) Analogous organs
C) Fossils
D) Embryos
✅ Answer: B
9. Darwin's theory is based on: A) Mutation
B) Natural Selection
C) Cloning
D) Hybridization
✅ Answer: B
10. "Survival of the Fittest" was associated with: A) Darwin's theory
B) Cell theory
C) Germ theory
D) Atomic theory
✅ Answer: A
11. According to Lamarck, giraffes developed long necks due to: A) Natural selection
B) Use and disuse of organs
C) Mutation only
D) Fossil evidence
✅ Answer: B
12. Variations are important because they: A) Cause extinction only
B) Help in adaptation and evolution
C) Stop reproduction
D) Prevent survival
✅ Answer: B
13. Evolution occurs through: A) Sudden creation
B) Gradual accumulation of variations
C) Magic
D) Chance only
✅ Answer: B
14. Human evolution suggests humans evolved from: A) Modern monkeys
B) Ape-like ancestors
C) Fish
D) Birds
✅ Answer: B
15. Which is NOT evidence of evolution? A) Fossils
B) Embryology
C) Comparative anatomy
D) Photosynthesis
✅ Answer: D
16. The branch of science dealing with fossils is called: A) Ecology
B) Paleontology
C) Cytology
D) Anatomy
✅ Answer: B
17. Which statement is correct? A) Evolution occurs in a single generation.
B) Evolution is a slow process.
C) Evolution stops after species formation.
D) Evolution occurs only in animals.
✅ Answer: B
18. Analogous organs have: A) Same origin, different function
B) Different origin, same function
C) Same origin, same function
D) No function
✅ Answer: B
19. Fossils found in deeper rock layers are generally: A) Newer
B) Older
C) Larger
D) Smaller
✅ Answer: B
20. The ultimate source of variation is: A) Mutation
B) Digestion
C) Respiration
D) Excretion
✅ Answer: AScore Card
- 18–20 = NEET/Board Level Excellent 🔥
- 15–17 = Very Good ✅
- 10–14 = Good 👍
- Below 10 = Revise Evolution Again
Evolution (Class 10 Science) – Next 20 Tricky MCQs 🔥
21. Which of the following provides the strongest evidence for evolution? A) Respiration
B) Fossils
C) Nutrition
D) Excretion
✅ Answer: B
22. The term "speciation" refers to: A) Extinction of species
B) Formation of new species
C) Migration of species
D) Adaptation only
✅ Answer: B
23. Variations that help an organism survive are called: A) Harmful variations
B) Neutral variations
C) Adaptive variations
D) Vestigial variations
✅ Answer: C
24. Archaeopteryx is considered a connecting link between: A) Fish and Amphibians
B) Reptiles and Birds
C) Mammals and Birds
D) Reptiles and Mammals
✅ Answer: B
25. Which scientist proposed inheritance of acquired characters? A) Darwin
B) Lamarck
C) Mendel
D) Morgan
✅ Answer: B
26. The wings of a bat and the wings of a bird are: A) Analogous organs
B) Homologous organs
C) Vestigial organs
D) Rudimentary organs
✅ Answer: B
27. Which of the following is a vestigial organ in humans? A) Heart
B) Lungs
C) Appendix
D) Kidney
✅ Answer: C
28. Fossils are usually found in: A) Igneous rocks
B) Sedimentary rocks
C) Metamorphic rocks
D) Granite
✅ Answer: B
29. Which statement supports Darwin's theory? A) Organisms change because they need to.
B) Useful variations are selected by nature.
C) Acquired characters are inherited.
D) Evolution occurs suddenly.
✅ Answer: B
30. Evolutionary relationships can be studied using: A) DNA comparison
B) Fossils
C) Homologous organs
D) All of these
✅ Answer: D
31. The process by which better-adapted organisms survive and reproduce is: A) Mutation
B) Natural Selection
C) Fertilization
D) Hybridization
✅ Answer: B
32. Which is an example of analogous organs? A) Human arm and whale flipper
B) Bat wing and bird wing
C) Human arm and bat wing
D) Whale flipper and bat wing
✅ Answer: B
33. Evolution takes place at the level of: A) Individual
B) Population
C) Organ
D) Tissue
✅ Answer: B
34. The similarity in embryos of different vertebrates suggests: A) Common ancestry
B) Different ancestry
C) Extinction
D) Mutation only
✅ Answer: A
35. Which of the following is NOT a factor in natural selection? A) Variation
B) Competition
C) Overproduction
D) Photosynthesis
✅ Answer: D
36. The modern human is known as: A) Homo erectus
B) Homo habilis
C) Homo sapiens
D) Australopithecus
✅ Answer: C
37. Evolution explains: A) Diversity of life forms
B) Origin of species
C) Adaptations
D) All of these
✅ Answer: D
38. The oldest fossils are generally found in: A) Upper rock layers
B) Deepest rock layers
C) Soil surface
D) Water bodies
✅ Answer: B
39. Which of the following is NOT evidence of common ancestry? A) Homologous organs
B) Embryological similarities
C) Fossils
D) Analogous organs
✅ Answer: D
40. Darwin observed natural selection during his voyage on: A) HMS Victory
B) HMS Beagle
C) Titanic
D) Mayflower
✅ Answer: BPYQ Trick Question 🚨
41. Evolution cannot be equated with progress because: A) Evolution always produces better organisms
B) Evolution only increases complexity
C) Evolution is simply change over generations, not necessarily improvement
D) Evolution stops after adaptation
✅ Answer: CRelated posts
- Class10 how do organisms reproduce. https://www.learnwithafsa.online/2026/05/how-do-organisms-reproduce-class-10-notes.html
- https://www.learnwithafsa.online/2026/05/class-10-notes-cbse.html
- https://www.learnwithafsa.online/2026/05/life-processes-class-10-notes.html