Class 10 Science – Heredity | Interactive Visual Revision Notes

1. Classroom Notes

Real-world connection: Just like you automatically inherit your family surname, you inherit traits such as eye colour, height, and the shape of your ears — from your parents. Heredity is nature's own recipe, copied from generation to generation through tiny chemical instructions called genes.

Topic 1: What is Heredity?

Children look like their parents.
Traits pass from parents to children.
Eye colour comes from your parents.
Height also comes from your family.
This passing of traits is heredity.

Topic 2: Accumulation of Variation

Each generation adds small changes.
Changes build up over time.
After many generations, big differences appear.
This helps species survive better.
Variation gives more choices to nature.

Topic 3: Inherited Traits

Some traits come from parents only.
Free earlobes or attached earlobes.
Curly hair or straight hair.
Rolling tongue is an inherited trait.
These traits follow set rules.

Topic 4: Mendel's Experiments

Gregor Mendel studied pea plants.
He crossed tall and short plants.
All babies were tall plants.
He found rules of inheritance.
Mendel is father of genetics.

Topic 5: Dominant and Recessive Traits

Some traits are stronger than others.
Tall is dominant over short.
Strong traits show up in babies.
Weak traits hide but stay inside.
We call weak traits recessive.

Topic 6: F1 and F2 Generation

F1 means first baby generation.
F1 plants all looked the same.
F1 plants were crossed again.
F2 showed both tall and short.
Ratio was three tall, one short.

Topic 7: How Traits Get Expressed

Genes carry instructions for traits.
Each trait has two gene copies.
One copy from mother, one from father.
Dominant gene wins and shows up.
Recessive gene hides behind dominant one.

Topic 8: Sex Determination

Humans have 23 pairs of chromosomes.
Last pair decides boy or girl.
Girls have XX chromosomes.
Boys have XY chromosomes.
Father's chromosome decides the baby's sex.

Topic 9: Genes and Chromosomes

Genes sit on threads called chromosomes.
Each cell has 46 chromosomes total.
Chromosomes come in matching pairs.
DNA makes up the chromosomes.
Genes are small parts of DNA.

Topic 10: Evolution and Traits

Useful traits help animals survive better.
These traits pass to next generation.
Over time, species slowly change.
This slow change is called evolution.
Heredity drives evolution forward.

3. Worked Examples

Example 1: Mendel's Cross: Tall x Short

1 Parent tall plant is TT.

2 Parent short plant is tt.

3 Each gives one gene to baby.

4 Baby gets T from tall, t from short.

5 Baby is Tt, which looks tall.

Answer: All F1 plants are tall (Tt).

Example 2: Punnett Square for F2

1 Cross Tt with Tt.

2 Make a 2x2 box.

3 Top: T and t. Side: T and t.

4 Fill in: TT, Tt, Tt, tt.

5 Count: 3 tall, 1 short.

Answer: 3 tall plants, 1 short plant (3:1 ratio).

Example 3: Will the baby be a boy or girl?

1 Mother always gives X chromosome.

2 Father can give X or Y.

3 If father gives X, baby is XX (girl).

4 If father gives Y, baby is XY (boy).

5 Each option has 50% chance.

Answer: Father's chromosome decides the sex. 50% chance each.

4. Cheat Sheet

Term	Meaning
Heredity	Traits passing from parents to children
Gene	Instruction for one trait
Chromosome	Long thread carrying many genes
DNA	Chemical that makes up genes
Dominant	Trait that always shows up
Recessive	Trait that hides behind dominant
F1 Generation	First set of baby organisms
F2 Generation	Babies of F1 organisms
Punnett Square	Box to predict baby traits
Variation	Small differences between organisms
Sex Determination	How boy or girl is decided
Evolution	Slow change in species over time

5. Take-Home Handout

Part A: Fill in the Blanks

1. Passing of traits from parents is called __________.
2. __________ studied pea plants and found rules.
3. A trait that always shows up is __________.
4. A trait that hides is called __________.
5. Genes sit on long threads called __________.

Part B: True or False

1. Children always look exactly like their parents. ( )
2. Mendel used pea plants in his experiments. ( )
3. A recessive trait always shows up. ( )
4. Girls have XX chromosomes. ( )
5. Mother's chromosome decides the baby's sex. ( )

Part C: Solve These Problems

Problem 1: A tall plant (TT) is crossed with a short plant (tt). What will the F1 babies look like?

Problem 2: Two Tt plants are crossed. Draw a Punnett square and find the ratio.

Problem 3: A mother (XX) and father (XY) have a baby. What are the possible combinations?

Part D: Match the Columns

Column A	Column B
1. Heredity	a. Box to predict traits
2. Dominant	b. Passing of traits
3. DNA	c. Trait that shows up
4. Punnett Square	d. Chemical making up genes
5. Evolution	e. Slow change over time

Part E: Draw and Label

Draw a Punnett square for Tt x Tt cross. Label dominant and recessive results.

✅ Detailed Solutions – Section 5 Handout

Part A: Fill in the Blanks

1 Passing of traits from parents is called Heredity.

2 Mendel studied pea plants and found the rules of inheritance.

3 A trait that always shows up is called Dominant.

4 A trait that hides is called Recessive.

5 Genes sit on long threads called Chromosomes.

Part B: True or False

1 False. Children look similar to parents, but small differences (variation) appear every generation.

2 True. Gregor Mendel used pea plants in his famous inheritance experiments.

3 False. A recessive trait hides behind the dominant one. It shows only when two recessive copies are present (tt).

4 True. Girls have two X chromosomes (XX).

5 False. The father's chromosome decides the baby's sex — mother always gives X; father gives X (girl) or Y (boy).

Part C: Solved Problems

Problem 1 — Tall (TT) × Short (tt)

1 Tall parent is TT; short parent is tt.

2 Tall gives T; short gives t to each offspring.

3 All babies are Tt. T is dominant, so all look tall.

All F1 plants are Tall (Tt). 100% tall.

Problem 2 — Punnett Square: Tt × Tt

1 Draw a 2×2 box. Top: T, t. Side: T, t.

2 Fill cells: TT | Tt | Tt | tt.

3 TT = tall, Tt = tall, Tt = tall, tt = short.

Ratio = 3 Tall : 1 Short (3:1). Three plants tall, one plant short.

Problem 3 — Sex determination: XX × XY

1 Mother (XX) always gives X.

2 Father (XY) gives X or Y — equal chance.

3 X + X = XX → Girl. X + Y = XY → Boy.

50% chance Girl (XX), 50% chance Boy (XY). Father's chromosome decides.

Part D: Match the Columns

1 Heredity → b. Passing of traits

2 Dominant → c. Trait that shows up

3 DNA → d. Chemical making up genes

4 Punnett Square → a. Box to predict traits

5 Evolution → e. Slow change over time

Part E: Punnett Square – Tt × Tt (Description)

1 Write T and t across the top (one parent's gametes).

2 Write T and t down the left side (other parent's gametes).

3 Fill four cells: TT (top-left), Tt (top-right), Tt (bottom-left), tt (bottom-right).

1 TT (tall, dominant homozygous) + 2 Tt (tall, heterozygous) + 1 tt (short, recessive) → 3 Tall : 1 Short ratio.

Chapter 8: Heredity
Class 10 Science – Visual Revision Notes

Table of Contents

1. Classroom Notes

Topic 1: What is Heredity?

Topic 2: Accumulation of Variation

Topic 3: Inherited Traits

Topic 4: Mendel's Experiments

Topic 5: Dominant and Recessive Traits

Topic 6: F1 and F2 Generation

Topic 7: How Traits Get Expressed

Topic 8: Sex Determination

Topic 9: Genes and Chromosomes

Topic 10: Evolution and Traits

2. Easy Illustrations

Fig 1: Mendel's Pea Plant Cross

Fig 2: Dominant vs Recessive (Punnett Square)

Fig 3: Sex Determination in Humans

Fig 4: Chromosome Pairs in a Cell

Fig 5: Accumulation of Variation

3. Worked Examples

Example 1: Mendel's Cross: Tall x Short

Example 2: Punnett Square for F2

Example 3: Will the baby be a boy or girl?

4. Cheat Sheet

5. Take-Home Handout

Part A: Fill in the Blanks

Part B: True or False

Part C: Solve These Problems

Part D: Match the Columns

Part E: Draw and Label

✅ Detailed Solutions – Section 5 Handout

Part A: Fill in the Blanks

Part B: True or False

Part C: Solved Problems

Part D: Match the Columns

Part E: Punnett Square – Tt × Tt (Description)

6. Revision Flashcards

7. Mind Map

Chapter 8: HeredityClass 10 Science – Visual Revision Notes

Table of Contents

1. Classroom Notes

Topic 1: What is Heredity?

Topic 2: Accumulation of Variation

Topic 3: Inherited Traits

Topic 4: Mendel's Experiments

Topic 5: Dominant and Recessive Traits

Topic 6: F1 and F2 Generation

Topic 7: How Traits Get Expressed

Topic 8: Sex Determination

Topic 9: Genes and Chromosomes

Topic 10: Evolution and Traits

2. Easy Illustrations

Fig 1: Mendel's Pea Plant Cross

Fig 2: Dominant vs Recessive (Punnett Square)

Fig 3: Sex Determination in Humans

Fig 4: Chromosome Pairs in a Cell

Fig 5: Accumulation of Variation

3. Worked Examples

Example 1: Mendel's Cross: Tall x Short

Example 2: Punnett Square for F2

Example 3: Will the baby be a boy or girl?

4. Cheat Sheet

5. Take-Home Handout

Part A: Fill in the Blanks

Part B: True or False

Part C: Solve These Problems

Part D: Match the Columns

Part E: Draw and Label

✅ Detailed Solutions – Section 5 Handout

Part A: Fill in the Blanks

Part B: True or False

Part C: Solved Problems

Part D: Match the Columns

Part E: Punnett Square – Tt × Tt (Description)

6. Revision Flashcards

7. Mind Map

Chapter 8: Heredity
Class 10 Science – Visual Revision Notes