HEREDITY — QUESTION BANK

Class 10 Science | Chapter 8

A. MCQs — Multiple Choice Questions

1.

The differences found among individuals of the same species are called:

A. Heredity
B. Variations
C. Reproduction
D. Evolution

Answer: B

2.

Variation is generally greater in:

A. Asexual reproduction
B. Sexual reproduction
C. Vegetative reproduction only
D. Binary fission

Answer: B

3.

Minor variations in asexually reproducing organisms can arise mainly because of:

A. Different environments
B. Inaccuracies during DNA copying
C. Different chromosome numbers
D. Lack of genes

Answer: B

4.

The transmission of traits from parents to offspring is called:

A. Variation
B. Heredity
C. Selection
D. Reproduction

Answer: B

5.

Who established important rules of inheritance through experiments on pea plants?

A. Charles Darwin
B. Gregor Johann Mendel
C. Lamarck
D. Watson

Answer: B

6.

Mendel mainly used which organism for his experiments?

A. Bacteria
B. Garden pea
C. Fruit fly
D. Human beings

Answer: B

7.

Which of the following was studied by Mendel?

A. Tall and short plants
B. Round and wrinkled seeds
C. Violet and white flowers
D. All of the above

Answer: D

8.

When a tall pea plant is crossed with a short pea plant, the F₁ generation contains:

A. Only short plants
B. Only tall plants
C. Both tall and short plants
D. Medium-height plants

Answer: B

9.

The absence of medium-height plants in Mendel’s F₁ generation suggests that:

A. Traits always blend
B. One parental trait can dominate over the other
C. Traits are not inherited
D. Only the mother contributes genetic material

Answer: B

10.

If TT represents tallness and tt represents shortness, the genotype of an F₁ tall plant is:

A. TT only
B. tt only
C. Tt
D. TTT

Answer: C

11.

In the cross Tt × Tt, the genotype ratio is:

A. 3 : 1
B. 1 : 1
C. 1 : 2 : 1
D. 9 : 3 : 3 : 1

Answer: C

12.

In the cross Tt × Tt, the phenotype ratio is:

A. 1 tall : 1 short
B. 3 tall : 1 short
C. 1 tall : 3 short
D. 1 : 2 : 1

Answer: B

13.

Which genotype produces the recessive phenotype in Mendel’s pea plant example?

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

Answer: C

14.

A trait expressed even when only one copy of its allele is present is called:

A. Recessive
B. Dominant
C. Acquired
D. Environmental

Answer: B

15.

A recessive trait is expressed when:

A. One recessive copy is present
B. Both copies are recessive
C. One dominant copy is present
D. No genes are present

Answer: B

16.

Which pair represents a heterozygous genotype?

A. TT
B. tt
C. Tt
D. XX

Answer: C

17.

Which pair represents a homozygous genotype?

A. Tt
B. Rr
C. TT
D. XY

Answer: C

18.

In a dihybrid cross involving seed shape and seed colour, Mendel observed an F₂ phenotypic ratio of:

A. 3 : 1
B. 1 : 2 : 1
C. 9 : 3 : 3 : 1
D. 1 : 1

Answer: C

19.

The appearance of tall plants with wrinkled seeds and short plants with round seeds in the F₂ generation demonstrates:

A. Blending inheritance
B. Independent inheritance of traits
C. Absence of variation
D. Asexual reproduction

Answer: B

20.

A section of DNA that provides information for making a protein is called:

A. Chromosome
B. Gene
C. Cell
D. Hormone

Answer: B

21.

DNA is the information source for making:

A. Proteins
B. Chromosomes only
C. Cells directly
D. Germ cells only

Answer: A

22.

Genes control traits primarily by influencing:

A. Protein production and function
B. The number of cells only
C. The size of chromosomes only
D. Environmental temperature

Answer: A

23.

A change in the gene for an enzyme involved in plant hormone production may affect:

A. Plant height
B. Seed number only
C. Flower colour only
D. Chromosome number

Answer: A

24.

In sexually reproducing organisms, each individual generally has:

A. One copy of every gene
B. Two copies of genes for the same trait
C. Three copies of every gene
D. No genes in germ cells

Answer: B

25.

Chromosomes are present as:

A. Independent pieces of DNA
B. Proteins only
C. Hormones
D. Cell walls

Answer: A

26.

In human beings, the number of pairs of autosomes is:

A. 21
B. 22
C. 23
D. 44

Answer: B

27.

The sex chromosomes of a human female are:

A. XY
B. XX
C. YY
D. XO

Answer: B

28.

The sex chromosomes of a human male are:

A. XX
B. XY
C. YY
D. XO

Answer: B

29.

A human egg normally carries:

A. X chromosome
B. Y chromosome
C. Either X or Y
D. Both X and Y

Answer: A

30.

A sperm carrying an X chromosome fertilising an egg produces:

A. XY
B. XX
C. YY
D. XO

Answer: B

31.

A sperm carrying a Y chromosome fertilising an egg produces:

A. XX
B. XY
C. YY
D. XO

Answer: B

32.

According to the chromosome mechanism described in the chapter, the sex of the child is determined by:

A. The mother’s chromosome only
B. The paternal X or Y chromosome
C. Environmental temperature in humans
D. The number of autosomes

Answer: B

33.

Which organism mentioned in the chapter can use environmental temperature as a sex-determining factor?

A. Humans
B. Some reptiles
C. Pea plants
D. Bacteria

Answer: B

34.

Which organisms mentioned in the chapter can change sex?

A. Some snails
B. Humans
C. Pea plants
D. Bacteria

Answer: A

35.

The fusion of two germ cells restores:

A. Half the chromosome number
B. The normal chromosome number of the species
C. Only paternal chromosomes
D. Only maternal chromosomes

Answer: B

B. Assertion–Reason Questions

Choose:

A. Both A and R are true, and R correctly explains A.
B. Both A and R are true, but R does not correctly explain A.
C. A is true, but R is false.
D. A is false, but R is true.

1.

Assertion: Sexual reproduction generally produces greater variation than asexual reproduction.

Reason: Genetic material comes from two parents during sexual reproduction.

Answer: A

2.

Assertion: All F₁ plants in Mendel’s tall × short cross were medium height.

Reason: Traits from both parents always blend together.

Answer: D

3.

Assertion: A recessive trait can remain unexpressed in an individual.

Reason: A dominant allele can mask the expression of a recessive allele.

Answer: A

4.

Assertion: The F₂ generation of a monohybrid cross can contain short plants even though all F₁ plants were tall.

Reason: The F₁ tall plants can carry the recessive allele without expressing it.

Answer: A

5.

Assertion: The genotype ratio in Tt × Tt is 1 : 2 : 1.

Reason: The possible genotypes are TT, Tt, Tt and tt.

Answer: A

6.

Assertion: Traits can appear in new combinations in the F₂ generation.

Reason: Different traits can be inherited independently.

Answer: A

7.

Assertion: Genes control characteristics.

Reason: Genes provide information involved in making proteins that can influence traits.

Answer: A

8.

Assertion: Every human child receives an X chromosome from the mother.

Reason: Human eggs carry an X chromosome.

Answer: A

9.

Assertion: A father can contribute either an X or a Y chromosome to a child.

Reason: Human males have XY sex chromosomes.

Answer: A

10.

Assertion: Germ cells contain one chromosome from each chromosome pair.

Reason: Fusion of two germ cells restores the normal chromosome number.

Answer: B

C. Fill in the Blanks

1.

The transmission of characteristics from parents to offspring is called ________.

Answer: heredity

2.

Differences among individuals of the same species are called ________.

Answer: variations

3.

Sexual reproduction generally produces ________ variation than asexual reproduction.

Answer: greater

4.

Gregor Johann Mendel performed his famous experiments using ________ plants.

Answer: pea

5.

Mendel studied contrasting characters such as tall/short and round/________ seeds.

Answer: wrinkled

6.

The first generation obtained from a parental cross is called the ________ generation.

Answer: F₁

7.

The second generation obtained by reproduction of F₁ individuals is called the ________ generation.

Answer: F₂

8.

A trait that is expressed even when present in one copy is called a ________ trait.

Answer: dominant

9.

A trait expressed only when both copies are recessive is called a ________ trait.

Answer: recessive

10.

The F₂ phenotypic ratio in a monohybrid cross is ________.

Answer: 3 : 1

11.

The F₂ genotypic ratio in a monohybrid cross is ________.

Answer: 1 : 2 : 1

12.

The F₂ phenotypic ratio in the dihybrid cross discussed in the chapter is ________.

Answer: 9 : 3 : 3 : 1

13.

A section of DNA that provides information for making a protein is called a ________.

Answer: gene

14.

DNA is the information source for making ________ in cells.

Answer: proteins

15.

Genes are located on structures called ________.

Answer: chromosomes

16.

Human females have ________ sex chromosomes.

Answer: XX

17.

Human males have ________ sex chromosomes.

Answer: XY

18.

A human egg always contributes an ________ chromosome.

Answer: X

19.

A sperm carrying a Y chromosome can produce an ________ offspring when it fuses with an X-bearing egg.

Answer: XY

20.

The fusion of two germ cells restores the normal ________ number of the species.

Answer: chromosome

D. True or False

1.

Variations can arise during asexual reproduction.

Answer: True

2.

Sexual reproduction generally produces less variation than asexual reproduction.

Answer: False

3.

Mendel used pea plants to study inheritance.

Answer: True

4.

All F₁ plants in Mendel’s tall × short cross were short.

Answer: False

5.

In the example used in the chapter, TT and Tt plants are tall.

Answer: True

6.

The genotype tt gives the tall phenotype.

Answer: False

7.

The recessive trait is expressed when both copies are recessive.

Answer: True

8.

The F₂ phenotypic ratio in the monohybrid example is 3 : 1.

Answer: True

9.

The F₂ genotypic ratio in the monohybrid example is 3 : 1.

Answer: False

10.

Different traits may be inherited independently.

Answer: True

11.

A gene is a section of DNA that provides information for making a protein.

Answer: True

12.

Every body cell has only one copy of each chromosome.

Answer: False

13.

Human females are XX.

Answer: True

14.

Human males are XX.

Answer: False

15.

A human mother can contribute either X or Y through her egg.

Answer: False

16.

A human father can contribute either X or Y through sperm.

Answer: True

17.

Some reptiles use temperature as a sex-determining factor.

Answer: True

18.

All species determine sex using the same mechanism.

Answer: False

E. Match the Following

Set 1

Column A	Column B
1. Heredity	A. Section of DNA
2. Variation	B. Transmission of traits
3. Gene	C. Difference among individuals
4. Chromosome	D. DNA-containing structure carrying genes

Answers:
1–B, 2–C, 3–A, 4–D

Set 2

Column A	Column B
1. TT	A. Recessive phenotype
2. Tt	B. Tall phenotype
3. tt	C. Heterozygous
4. T	D. Dominant allele

Answers:
1–B, 2–C, 3–A, 4–D

Set 3

Column A	Column B
1. F₁	A. Second generation
2. F₂	B. First generation
3. XX	C. Human female
4. XY	D. Human male

Answers:
1–B, 2–A, 3–C, 4–D

F. Very Short Answer Questions

1.

What is heredity?

Answer: Heredity is the transmission of traits from parents to offspring.

2.

What is variation?

Answer: Variation refers to differences among individuals of the same species.

3.

Name the scientist who established important rules of inheritance using pea plants.

Answer: Gregor Johann Mendel.

4.

Name the organism used by Mendel in his experiments.

Answer: Garden pea.

5.

What is a dominant trait?

Answer: A trait that is expressed when its allele is present in a single copy.

6.

What is a recessive trait?

Answer: A trait that is expressed when both copies are recessive.

7.

What is a gene?

Answer: A section of DNA that provides information for making a protein.

8.

What are chromosomes?

Answer: Chromosomes are separate DNA-containing structures that carry genes.

9.

What are the sex chromosomes of a human female?

Answer: XX.

10.

What are the sex chromosomes of a human male?

Answer: XY.

11.

Which chromosome does a human mother contribute through the egg?

Answer: X chromosome.

12.

Which chromosomes can a human father contribute through sperm?

Answer: X or Y chromosome.

13.

What is the phenotypic ratio in Mendel’s monohybrid F₂ generation?

Answer: 3 : 1.

14.

What is the genotypic ratio in the same F₂ generation?

Answer: 1 : 2 : 1.

15.

What is the dihybrid F₂ phenotypic ratio described in the chapter?

Answer: 9 : 3 : 3 : 1.

G. Short Answer Questions

1.

Why does sexual reproduction produce greater variation than asexual reproduction?

2.

How can variation help an organism survive?

3.

How did Mendel’s pea plant experiments demonstrate dominance?

4.

Why were all F₁ plants tall when Mendel crossed tall and short pea plants?

5.

Why did short plants reappear in the F₂ generation?

6.

Differentiate between a dominant and a recessive trait.

7.

Explain the difference between genotype and phenotype using TT, Tt and tt.

8.

How did Mendel demonstrate independent inheritance of traits?

9.

How can new combinations of traits appear in offspring?

10.

How do genes influence characteristics?

11.

Why do sexually reproducing organisms possess two copies of genes for a trait?

12.

Why must germ cells contain only one chromosome from each chromosome pair?

13.

How does fertilisation restore the normal chromosome number?

14.

Explain the XX–XY mechanism of sex determination in humans.

15.

Why is the paternal chromosome important in determining the sex chromosome combination of a human child?

H. Long Answer / 3–5 Mark Questions

1.

Explain Mendel’s monohybrid experiment using tall and short pea plants. Include the F₁ and F₂ generations and the important ratios.

2.

Explain how Mendel’s experiments established the concepts of dominant and recessive traits.

3.

Describe how Mendel’s dihybrid experiment demonstrates independent inheritance and the formation of new combinations.

4.

Explain the relationship between DNA, genes, proteins and traits using plant height as an example.

5.

Explain how chromosomes ensure equal genetic contribution from male and female parents in sexual reproduction.

6.

Describe the mechanism of sex determination in human beings using XX and XY chromosomes.

7.

Explain how variations arise during reproduction and why some variations may improve survival.

I. Case-Based Questions

Case 1 — Mendel’s Pea Plants

A researcher crosses a pure tall pea plant with a pure short pea plant. All plants in the first generation are tall. When these plants are allowed to reproduce, short plants appear in the next generation.

Questions

1. What does the first generation indicate about the two traits?

2. Which trait is dominant in this example?

3. What is the likely genotype of the F₁ plants?

4. What is the expected phenotype ratio in the F₂ generation?

Answers:

The tall trait is expressed while shortness remains unexpressed.
Tallness.
Tt.
3 tall : 1 short.

Case 2 — Two Traits in Peas

A cross involves seed shape and seed colour. The F₂ offspring show parental combinations as well as new combinations.

Questions

1. What principle does this observation demonstrate?

2. Name one new combination that may appear.

3. What F₂ phenotypic ratio is associated with the dihybrid cross discussed in the chapter?

4. Why do new combinations occur?

Answers:

Independent inheritance of traits.
Tall + wrinkled or short + round.
9 : 3 : 3 : 1.
Factors controlling different traits can recombine independently.

Case 3 — Genes and Plant Height

A change in a gene causes an enzyme involved in plant hormone production to become less efficient. The plant consequently produces less growth hormone and becomes shorter.

Questions

1. What does this example show about genes?

2. What is the role of the enzyme?

3. How can a change in DNA affect a visible characteristic?

Answers:

Genes control characteristics by influencing proteins.
It participates in a process involved in producing the growth hormone.
A change in the gene can alter the protein/enzyme’s efficiency, affecting hormone production and ultimately the trait.

Case 4 — Human Sex Determination

A human female has XX sex chromosomes and a human male has XY sex chromosomes. The egg contributes X, while sperm can contribute either X or Y.

Questions

1. What chromosome does every child receive from the mother?

2. What are the two possible sex-chromosome combinations?

3. Which parental contribution determines whether the combination is XX or XY?

4. What is the expected proportion of XX and XY combinations?

Answers:

X.
XX and XY.
The paternal chromosome.
Approximately 1 : 1.

J. HOTS / Application Questions

1.

A population contains a variation that allows some bacteria to survive unusually high temperatures. A heat wave occurs. Explain why this variation could become advantageous.

2.

A tall pea plant is crossed with a short pea plant, and some offspring are short. What can you infer about the genotype of the tall parent?

Answer: The tall parent must carry the recessive allele; its genotype is Tt.

3.

Two tall pea plants produce a short offspring. What does this tell you about the parents’ genetic make-up?

Answer: Both parents must have carried the recessive allele, so they can be represented as Tt.

4.

A student says, “The dominant trait must always be the most common trait in a population.” Is this conclusion justified? Explain.

Answer: No. Dominance refers to expression of an allele in a particular genetic combination, not how frequently the trait occurs in a population.

5.

Why can two parents with the same visible trait produce offspring showing a different trait?

Answer: The parents may carry a recessive allele that is not expressed in them but can combine in the offspring.

6.

If a child receives an X chromosome from the mother and a Y chromosome from the father, what is the chromosome combination?

Answer: XY.

7.

Why would inheritance of a complete set of chromosomes from each parent without reduction cause a problem?

Answer: The chromosome number would not remain stable across generations. Reduction in germ cells and restoration during fertilisation maintains the species’ normal chromosome number.

K. Diagram / Genetic Cross Questions

1.

Complete the cross:

TT × tt

Gametes: ________ and ________

F₁ genotype: ________

F₁ phenotype: ________

Answer:
Gametes: T and t
F₁ genotype: Tt
F₁ phenotype: Tall

2.

Complete:

Tt × Tt

Possible offspring:

TT, ________, ________, tt

Genotypic ratio: ________

Phenotypic ratio: ________

Answer:
Tt, Tt
1 : 2 : 1
3 : 1

3.

If T represents tallness and t represents shortness, identify the phenotype:

Genotype	Phenotype
TT	______
Tt	______
tt	______

Answer:
TT → Tall
Tt → Tall
tt → Short

4.

Complete the human sex-determination combinations:

Mother: X

Father: X or Y

X + X → ________

X + Y → ________

Answer:
XX
XY

L. “Give Reason” Questions

1.

Why is variation important for a species?

2.

Why does sexual reproduction produce greater diversity?

3.

Why did Mendel conclude that the tall and short traits did not blend?

4.

Why can a dominant trait be expressed in a heterozygous individual?

5.

Why does the recessive trait appear in the F₂ generation?

6.

Why can new combinations of traits occur in the F₂ generation?

7.

Why are genes considered the units that influence inherited characteristics?

8.

Why do germ cells contain only one chromosome from each pair?

9.

Why does fertilisation restore the normal chromosome number?

10.

Why can the father’s contribution determine whether a human child has XX or XY chromosomes?

M. “Differentiate Between” Questions

1.

Differentiate between heredity and variation.

2.

Differentiate between dominant and recessive traits.

3.

Differentiate between genotype and phenotype.

4.

Differentiate between F₁ and F₂ generations.

5.

Differentiate between asexual and sexual reproduction with respect to variation.

6.

Differentiate between XX and XY chromosome combinations in humans.

N. Numerical / Data-Based Questions

1.

In an F₂ generation, 400 offspring are produced from a monohybrid cross. If the expected phenotype ratio is 3 : 1, how many are expected to show the dominant phenotype and how many the recessive phenotype?

Answer:
Dominant = 300
Recessive = 100

2.

A dihybrid cross produces 1600 offspring. According to the 9 : 3 : 3 : 1 ratio, how many are expected in each phenotypic category?

Answer:
9/16 × 1600 = 900
3/16 × 1600 = 300
3/16 × 1600 = 300
1/16 × 1600 = 100

3.

In a monohybrid F₂ generation, what fraction is expected to have genotype Tt?

Answer: 2/4 = 1/2

4.

What fraction of F₂ offspring is expected to show the recessive phenotype in a Tt × Tt cross?

Answer: 1/4

5.

What fraction of offspring is expected to show the dominant phenotype in the same cross?

Answer: 3/4

O. NCERT-Style Concept Questions

1.

If a trait occurs in 10% of an asexually reproducing population while another occurs in 60%, can frequency alone prove which trait arose earlier?

Answer: No. Frequency alone does not establish the exact time at which a variation arose.

2.

How does creation of variations promote survival?

Answer: Some variations may provide an advantage under particular environmental conditions, allowing individuals with those variations to survive better.

3.

How do Mendel’s experiments show that traits may be dominant or recessive?

Answer: In the F₁ generation, only one parental trait is expressed. In F₂, the other trait reappears, showing that it was inherited but masked in F₁.

4.

How do Mendel’s experiments show that traits are inherited independently?

Answer: In the dihybrid cross, new combinations of seed shape and seed colour appear in F₂, showing that the traits can be inherited independently.

5.

A person has blood group A and another has blood group O. Their child has blood group O. Can this information alone tell us which blood group is dominant?

Answer: No. The observation alone is insufficient to establish dominance because the actual genetic combinations must be considered.

6.

How is equal genetic contribution from male and female parents ensured?

Answer: Germ cells carry one chromosome from each chromosome pair. During fertilisation, one germ cell from each parent combines, restoring the normal chromosome number.

P. Assertion / Concept Challenge

1.

A pea plant is tall. Can we determine from its appearance alone whether its genotype is TT or Tt?

Answer: No.

2.

A pea plant is short. Can its genotype be determined in the chapter’s example?

Answer: Yes. It must be tt.

3.

Can two organisms with the same phenotype have different genotypes?

Answer: Yes. TT and Tt both produce tall plants in the example.

4.

Can a recessive trait be inherited without being expressed?

Answer: Yes. For example, a Tt plant carries the recessive t allele but is tall.

5.

Can offspring show combinations of traits that neither parent displays as a combination?

Answer: Yes. Independent inheritance can produce new combinations.

Q. One-Word / One-Term Questions

Transmission of traits → Heredity
Differences among individuals → Variation
Scientist who studied pea inheritance → Mendel
Organism used by Mendel → Garden pea
First generation → F₁
Second generation → F₂
Expressed allele in a heterozygous condition → Dominant
Masked allele in a heterozygous condition → Recessive
DNA segment coding for a protein → Gene
DNA-containing genetic structures → Chromosomes
Female sex chromosomes → XX
Male sex chromosomes → XY
F₂ monohybrid phenotype ratio → 3 : 1
F₂ monohybrid genotype ratio → 1 : 2 : 1
F₂ dihybrid phenotype ratio → 9 : 3 : 3 : 1