Difference Between Dominant and Recessive Traits (NCERT Notes)

Introduction

Traits are the characteristics or features of an organism that are inherited from parents. According to NCERT Class 10 Science (Heredity and Evolution), traits are controlled by genes. When two different forms of a gene (alleles) are present together, one may express itself while the other remains hidden.

These traits are classified into:

Dominant Traits
Recessive Traits

What is a Dominant Trait?

A dominant trait is a trait that expresses itself even when only one copy of the dominant allele is present.

Key Points

Represented by a capital letter (e.g., T).
Expressed in both homozygous dominant (TT) and heterozygous (Tt) conditions.
Masks the effect of the recessive trait.
Appears in the first filial generation (F₁ generation).

Examples of Dominant Traits

Trait	Dominant Form
Plant Height	Tall (T)
Seed Shape	Round (R)
Flower Color in Pea Plant	Purple (P)
Tongue Rolling (Human)	Can Roll Tongue

What is a Recessive Trait?

A recessive trait is a trait that is expressed only when both alleles are recessive.

Key Points

Represented by a small letter (e.g., t).
Expressed only in homozygous recessive (tt) condition.
Remains hidden when a dominant allele is present.
Reappears in the F₂ generation.

Examples of Recessive Traits

Trait	Recessive Form
Plant Height	Dwarf (t)
Seed Shape	Wrinkled (r)
Flower Color	White (p)
Attached Earlobes	Recessive Trait

Dominant vs Recessive Traits

Feature	Dominant Trait	Recessive Trait
Expression	Appears with one dominant allele	Appears only with two recessive alleles
Symbol	Capital Letter (T)	Small Letter (t)
Visibility	Expressed in TT and Tt	Expressed only in tt
Effect	Masks recessive trait	Hidden by dominant trait
Appearance in F₁ Generation	Present	Usually absent
Example	Tall Plant	Dwarf Plant

Mendel’s Experiment and Dominance

First Cross (Parental Generation)

Tall Plant (TT) × Dwarf Plant (tt)

Gametes

Tall Plant → T
Dwarf Plant → t

F₁ Generation

All offspring become:

Tt (Tall)

This shows that the tall trait is dominant.

Punnett Square

	T	T
t	Tt	Tt
t	Tt	Tt

Result:

100% Tall Plants
Dominant trait expressed

Reappearance of Recessive Trait in F₂ Generation

When F₁ plants (Tt) are self-pollinated:

Tt × Tt

Punnett Square

	T	t
T	TT	Tt
t	Tt	tt

Genotypic Ratio

1 TT : 2 Tt : 1 tt

Phenotypic Ratio

3 Tall : 1 Dwarf

This proves that the recessive trait was present but hidden in the F₁ generation.

Characteristics of Dominant Traits

Expressed even with one dominant allele.
Represented by capital letters.
Appear in F₁ generation.
Suppress recessive traits.
Easier to observe in offspring.

Characteristics of Recessive Traits

Expressed only when both alleles are recessive.
Represented by small letters.
Hidden in heterozygous condition.
Reappear in F₂ generation.
Can remain unexpressed for generations.

Real-Life Examples

Characteristic	Dominant Trait	Recessive Trait
Pea Plant Height	Tall	Dwarf
Seed Shape	Round	Wrinkled
Flower Color	Purple	White
Human Earlobes	Free Earlobes	Attached Earlobes
Tongue Rolling	Can Roll	Cannot Roll

Importance of Dominant and Recessive Traits

Helps understand heredity.
Explains inheritance patterns.
Useful in genetics and breeding programs.
Assists in predicting offspring characteristics.
Helps study genetic disorders.

NCERT Summary

Traits are controlled by genes.
Dominant traits express themselves even in heterozygous condition.
Recessive traits express only in homozygous condition.
Dominant traits mask recessive traits.
Mendel’s experiments established the concept of dominance and recessiveness.
Recessive traits may remain hidden for generations and reappear later.

Practice Questions with Answers

1. What is a dominant trait?

Answer: A dominant trait is a trait that expresses itself even when only one dominant allele is present.

2. What is a recessive trait?

Answer: A recessive trait is expressed only when both alleles are recessive.

3. Why are all F₁ plants tall in Mendel’s experiment?

Answer: Because the tall allele (T) is dominant over the dwarf allele (t).

4. Which trait appears in F₂ generation after remaining hidden?

Answer: Recessive trait.

5. What is the phenotypic ratio in F₂ generation?

Answer: 3 Tall : 1 Dwarf.

Fill in the Blanks

A dominant trait is represented by a __________ letter.
Answer: Capital
A recessive trait is represented by a __________ letter.
Answer: Small
Tallness in pea plants is a __________ trait.
Answer: Dominant
Dwarfness in pea plants is a __________ trait.
Answer: Recessive
Recessive traits appear only in __________ condition.
Answer: Homozygous
The genotype of a dwarf pea plant is __________.
Answer: tt
Mendel worked on __________ plants.
Answer: Pea
The dominant allele masks the __________ allele.
Answer: Recessive
F₁ generation of TT × tt is __________.
Answer: Tt
Traits are controlled by __________.
Answer: Genes

MCQs (Multiple Choice Questions)

1. Which trait is expressed in heterozygous condition?

A) Recessive
B) Hidden
C) Dominant
D) Mutant

Answer: C) Dominant

2. Which symbol represents a recessive allele?

A) T
B) R
C) P
D) t

Answer: D) t

3. Which genotype shows a recessive trait?

A) TT
B) Tt
C) tt
D) TTT

Answer: C) tt

4. Who discovered the laws of inheritance?

A) Darwin
B) Mendel
C) Lamarck
D) Watson

Answer: B) Mendel

5. Tallness in pea plants is:

A) Recessive
B) Dominant
C) Hidden
D) Mutation

Answer: B) Dominant

6. Dwarfness in pea plants is:

A) Dominant
B) Codominant
C) Recessive
D) Hybrid

Answer: C) Recessive

7. Which generation shows only tall plants in Mendel’s first cross?

A) P Generation
B) F₂ Generation
C) F₁ Generation
D) F₃ Generation

Answer: C) F₁ Generation

8. What is the phenotypic ratio in F₂ generation?

A) 1:1
B) 2:1
C) 3:1
D) 1:2:1

Answer: C) 3:1

9. Which allele masks another allele?

A) Recessive
B) Dominant
C) Mutated
D) Hybrid

Answer: B) Dominant

10. Genes are responsible for:

A) Respiration
B) Nutrition
C) Traits
D) Digestion

Answer: C) Traits

Quick Revision Table

Dominant Trait	Recessive Trait
Expressed in TT and Tt	Expressed only in tt
Capital Letter	Small Letter
Masks other trait	Hidden by dominant trait
Appears in F₁ generation	Reappears in F₂ generation
Example: Tall Plant	Example: Dwarf Plant

One-Line Revision:
Dominant traits are expressed even with one dominant allele, whereas recessive traits are expressed only when both alleles are recessive. ✅