---
title: "Heredity: CBSE Class 10 Science previous year questions"
url: https://www.swavid.com/cbse/class-10/science/pyq/heredity
---

# Heredity: CBSE Class 10 Science previous year questions

18 questions from CBSE Class 10 board papers, newest first, each with full working.

## CBSE Class 10 Science Question Paper 2026 (Set 31/1/1) with Solutions

### Question 6

*1 mark · MCQ*

Sex is determined by different factors in various species. However, in human beings, it is determined genetically. Which amongst the following option(s) is/are correct for human beings ?

- (ii) and (iii)
- (i) only
- (i) and (iii)
- (iii) only

**Solution**

1. Human females have two X chromosomes ($XX$) and produce all gametes (ova) carrying an X chromosome.
2. Human males have an X and a Y chromosome ($XY$) and produce two types of gametes in equal proportion: one carrying an X chromosome and the other carrying a Y chromosome.
3. Therefore, statements (ii) and (iii) correctly describe the gametes carrying sex chromosomes from the male parent that determine the sex of the child upon fusion with the female gamete.

**Answer:** (a) (ii) and (iii)

> Common mistake: Confusing the contribution of male and female parents, or incorrectly selecting only one of the male gamete types.

### Question 15

*4 marks · Long answer*

Mendel took garden pea plants with different characteristics, such as height to study the inheritance pattern of factors (genes). He crossed tall pea plant with short pea plant and obtained all the tall plants in the $F_1$ generation.
Answer the following questions :
(a) Why only tall pea plants were observed in $F_1$ progeny ?
(b) By which method did Mendel obtain $F_2$ progeny ?
(c) (i) Write one difference between dominant and recessive trait.

**Part (a)**

1. Only tall plants were observed because the trait for tallness is dominant over the trait for shortness.

Answer (a): Tallness is the dominant trait.

**Part (b)**

1. Mendel obtained the F2 progeny by self-pollinating the F1 generation plants.

Answer (b): Self-pollination of F1 plants.

**Part (c)(i)**

1. A dominant trait is expressed in the presence of a contrasting allele, while a recessive trait is expressed only in the presence of identical alleles.

Answer (c)(i): Dominant traits express in F1; recessive traits do not.

**Answer:** Mendel's experiments demonstrate the laws of inheritance.

> Common mistake: Stating that the short trait disappears; it is only masked.

### Question 15 (OR)

*2 marks · Short answer*

Mendel took garden pea plants with different characteristics, such as height to study the inheritance pattern of factors (genes). He crossed tall pea plant with short pea plant and obtained all the tall plants in the $F_1$ generation.
Answer the following questions :
(c) (ii) Write two observations made by Mendel about $F_1$ progeny.

**Part (c)(ii)**

1. All plants in the F1 generation were tall.
2. No plants of intermediate height were observed.

Answer (c)(ii): All F1 plants were tall and no medium-height plants were produced.

**Answer:** Mendel's observations on F1 progeny.

> Common mistake: Failing to mention the absence of intermediate height.

## CBSE Class 10 Science Question Paper 2025 (Set 31/1/1) with Solutions

### Question 11

*1 mark · MCQ*

If pea plants with round and green seeds ($RRyy$) are crossed with pea plants having wrinkled and yellow seeds ($rrYY$), the seeds developed by the plants of $F_1$ generation will be :

- 50% round and green
- 75% wrinkled and green
- 100% round and yellow
- 75% wrinkled and yellow

**Solution**

1. When a cross is made between pea plants with round green seeds ($RRyy$) and wrinkled yellow seeds ($rrYY$), the $F_1$ generation inherits one allele for each trait from each parent.
2. The resulting genotype is $RrYy$, which expresses the dominant traits, resulting in 100% round and yellow seeds.

**Answer:** (c) 100% round and yellow

> Common mistake: Confusing dominant and recessive traits in the F1 generation.

### Question 18

*1 mark · Assertion and reason*

Assertion (A) : A human child bears all the basic features of human beings.
Reason (R) : It looks exactly like its parents, showing very little variations.

- Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
- Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
- Assertion (A) is true, but Reason (R) is false.
- Assertion (A) is false, but Reason (R) is true.

**Solution**

1. A human child exhibits all basic human features due to heredity, making Assertion (A) true.
2. Reason (R) is false because offspring do not look exactly like their parents; sexual reproduction introduces significant variations.

**Answer:** Assertion (A) is true, but Reason (R) is false.

> Common mistake: Assuming children are exact biological clones of their parents.

### Question 30

*3 marks · Short answer*

(a) What are chromosomes ?
(b) Explain in brief how stability of DNA content of a species is ensured in sexually reproducing organisms ?

**Part a**

1. Chromosomes are highly condensed thread-like structures composed of DNA and proteins found in the nucleus of a cell, which carry hereditary information in the form of genes.

Answer a: Chromosomes are nuclear structures made of DNA and protein that carry hereditary information.

**Part b**

1. Sexually reproducing organisms produce specialized germ cells (gametes) that have half the number of chromosomes (haploid) found in normal body cells.
2. This reduction is brought about by a special type of cell division called meiosis.
3. When two gametes fuse during fertilization, the original number of chromosomes (diploid) is restored in the zygote, ensuring stability of DNA content of the species.

Answer b: Meiosis halves the chromosome number in gametes, and subsequent fertilization restores the original number in the offspring.

**Answer:** Chromosomes are thread-like structures of DNA and protein, and their constancy across generations is maintained by gamete formation involving meiosis.

> Common mistake: Omitting the roles of meiosis and fertilization in maintaining chromosome number.

## CBSE Class 10 Science Question Paper 2024 (Set 31/1/1) with Solutions

### Question 8

*1 mark · MCQ*

Consider the following statements :
(i) The sex of a child is determined by what it inherits from the mother.
(ii) The sex of a child is determined by what it inherits from the father.
(iii) The probability of having a male child is more than that of a female child.
(iv) The sex of a child is determined at the time of fertilisation when male and female gametes fuse to form a zygote.
The correct statements are :

- (i) and (iii)
- (ii) and (iv)
- (iii) and (iv)
- (i), (ii) and (iv)

**Solution**

1. Statement (ii) is correct because the sex of a child depends on whether the sperm carries an X or Y chromosome.
2. Statement (iv) is correct as sex is determined at the time of fertilisation when gametes fuse.

**Answer:** (b) (ii) and (iv)

> Common mistake: Assuming human reproductive cells (gametes) have pairs of chromosomes instead of a single set.

### Question 9

*1 mark · MCQ*

Chromosomes :
(i) carry hereditary information from parents to the next generation.
(ii) are thread like structures located inside the nucleus of an animal cell.
(iii) always exist in pairs in human reproductive cells.
(iv) are involved in the process of cell division.
The correct statements are :

- (i) and (ii)
- (iii) and (iv)
- (i), (ii) and (iv)
- (i) and (iv)

**Solution**

1. Chromosomes carry hereditary information (DNA) and are thread-like structures in the nucleus involved in cell division.
2. Human reproductive cells contain only half the number of chromosomes (unpaired single set), making statement (iii) incorrect.

**Answer:** (c) (i), (ii) and (iv)

> Common mistake: Believing that reproductive cells contain paired chromosomes.

### Question 38

*4 marks · Case-based*

Mendel worked out the rules of heredity by working on garden pea using a number of visible contrasting characters. He conducted several experiments by making a cross with one or two pairs of contrasting characters of pea plant. On the basis of his observations he gave some interpretations which helped to study the mechanism of inheritance.
(i) When Mendel crossed pea plants with pure tall and pure short characteristics to produce $F_1$ progeny, which two observations were made by him in $F_1$ plants?
(ii) Write one difference between dominant and recessive trait.
(iii) (A) In a cross with two pairs of contrasting characters
$\text{RRYY} \times \text{rryy}$
(Round Yellow) (Wrinkled Green)
Mendel observed 4 types of combinations in $\text{F}_2$ generation. By which method did he obtain $\text{F}_2$ generation ? Write the ratio of the parental combinations obtained and what conclusions were drawn from this experiment.

**Part (i)**

1. All $F_1$ plants were tall.
2. None of the $F_1$ plants were short (intermediate trait was not observed).

Answer (i): All plants were tall and no medium-sized plants were observed.

**Part (ii)**

1. A dominant trait expresses itself even in the presence of an alternative trait, whereas a recessive trait gets masked in the presence of a dominant trait.

Answer (ii): Dominant trait expresses in both homozygous and heterozygous conditions, while recessive trait expresses only in homozygous condition.

**Part (iii)**

1. He obtained the $\text{F}_2$ generation by self-pollinating the $\text{F}_1$ plants.
2. The ratio of parental combinations to new combinations in the dihybrid cross is $9:3:3:1$, where parental combinations are $9$ (round yellow) and $1$ (wrinkled green).
3. It was concluded that the two pairs of traits are inherited independently of each other (Law of Independent Assortment).

Answer (iii): Self-pollination; parental ratio is 9:1 (out of 9:3:3:1); traits are inherited independently.

**Answer:** Mendel observed tallness in F1 progeny, and obtained F2 generation through self-pollination.

> Common mistake: Forgetting that selfing of F1 progeny produces the F2 generation.

### Question 38 (OR)

*2 marks · Case-based*

(iii) (B) Justify the statement :
"It is possible that a trait is inherited but may not be expressed."

**Part (iii) (B)**

1. Every inherited trait is influenced by paternal and maternal DNA.
2. In a heterozygous condition, the recessive allele is inherited but remains unexpressed because the dominant allele suppresses its expression.

Answer (iii) (B): In a heterozygous individual, the recessive trait is inherited from one parent but is masked by the dominant allele, hence not expressed.

**Answer:** Recessive traits are inherited from both parents but remain unexpressed in the presence of a dominant allele.

> Common mistake: Writing that traits can be lost instead of being masked.

## CBSE Class 10 Science Question Paper 2023 (Set 31/1/1) with Solutions

### Question 10

*1 mark · MCQ*

The statement that correctly describes the characteristic(s) of a gene is :

- In individuals of a given species, a specific gene is located on a particular chromosome.
- A gene is not the information source for making proteins in the cell.
- Each chromosome has only one gene located all along its length.
- All the inherited traits in human beings are not controlled by genes.

**Solution**

1. A specific gene is located on a particular chromosome in individuals of a given species.
2. Chromosomes contain multiple genes, genes code for proteins, and inherited traits are controlled by genes.

**Answer:** (a) In individuals of a given species, a specific gene is located on a particular chromosome.

> Common mistake: Assuming each chromosome carries only one gene.

### Question 18

*1 mark · Assertion and reason*

Assertion (A) : Genes inherited from the parents decide the sex of a child.
Reason (R) : X chromosome in a male child is inherited from his father.

- Both (A) and (R) are true and (R) is the correct explanation of (A).
- Both (A) and (R) are true, but (R) is not the correct explanation of (A).
- (A) is true, but (R) is false.
- (A) is false, but (R) is true.

**Solution**

1. The sex of a child depends on whether the fertilizing sperm carries an X chromosome or a Y chromosome, making the Assertion true.
2. A male child inherits an X chromosome from his mother and a Y chromosome from his father, making the Reason false.

**Answer:** "(A) is true, but (R) is false."

> Common mistake: Assuming a male child inherits the X chromosome from his father.

### Question 38

*4 marks · Case-based*

In order to trace the inheritance of traits Mendel crossed pea plants having one contrasting character or a pair of contrasting characters. When he crossed pea plants having round and yellow seeds with pea plants having wrinkled and green seeds, he observed that no plants with wrinkled and green seeds were obtained in the $F_1$ generation. When the $F_1$ generation pea plants were cross-bred by self-pollination, the $F_2$ generation had seeds with different combinations of shape and colour also.
(a) Write any two pairs of contrasting characteristics of pea plant used by Mendel other than those mentioned above.
(b) Differentiate between dominant and recessive traits.
(c) State the ratio of the combinations observed in the seeds of $F_2$ generation (in the above case). What do you interpret from this result?

**Part (a)**

1. Pair 1: Tall / Dwarf stem height
2. Pair 2: Violet / White flower colour (or Inflated / Constricted pod shape)

Answer (a): Tall/dwarf stem and violet/white flowers

**Part (b)**

1. Dominant trait: The trait that expresses itself in the presence or absence of another contrasting trait in the $F_1$ generation.
2. Recessive trait: The trait that remains hidden or masked in the presence of a dominant trait and expresses only in homozygous condition.

Answer (b): Dominant traits express in $F_1$ while recessive traits remain hidden.

**Part (c)**

1. Ratio of combinations in $F_2$ generation: $9:3:3:1$ (Round yellow : Round green : Wrinkled yellow : Wrinkled green).
2. Interpretation: The two pairs of traits are inherited independently of each other (Law of Independent Assortment).

Answer (c): Ratio is 9:3:3:1; traits assort independently.

**Answer:** Contrasting traits include tall/dwarf stem, dominant traits express themselves while recessive remain hidden, and dihybrid ratio is 9:3:3:1 showing independent assortment.

> Common mistake: Confusing monohybrid phenotypic ratio (3:1) with dihybrid phenotypic ratio (9:3:3:1).

### Question 38 (OR)

*2 marks · Case-based*

Given below is a cross between a pure violet flowered pea plant (V) and a pure white flowered pea plant (v). Diagrammatically explain what type of progeny is obtained in $F_1$ generation and $F_2$ generation :
Pure violet flowered plant $\times$ Pure white flowered plant
($V\,V$) $\qquad\qquad\qquad\qquad$ ($v\,v$)

**Part (i)**

1. Parents: Pure violet ($V\,V$) $\times$ Pure white ($v\,v$)
2. $F_1$ generation: All plants are violet flowered with genotype $V\,v$ due to dominance of allele $V$.

Answer (i): All violet-flowered plants ($V\,v$)

**Part (ii)**

1. Selfing of $F_1$ ($V\,v \times V\,v$) yields $F_2$ generation.
2. $F_2$ progeny has phenotypic ratio $3:1$ (violet to white) and genotypic ratio $1:2:1$ ($V\,V : V\,v : v\,v$).

Answer (ii): 3 violet to 1 white flowered plants

**Answer:** F1 progeny are all violet-flowered (Vv) and F2 progeny show violet and white flowers in 3:1 ratio.

> Common mistake: Not showing genotypes alongside phenotypes in crosses.

## CBSE Class 10 Science Question Paper 2022 (Set 31/1/1) with Solutions

### Question 5

*2 marks · Short answer*

(a) What is variation ? List two main reasons that may lead to variation in a population.

**Solution**

1. Variation refers to the differences in characters or traits among individuals of the same species.
2. The two main reasons that lead to variation are inaccuracies during DNA copying and sexual reproduction through the combination of genes from two parents.

**Answer:** Variation is the occurrence of differences among individuals, caused by DNA copying errors and sexual reproduction.

> Common mistake: Omitting DNA copying errors as a source of variation in asexual organisms.

### Question 5 (OR)

*2 marks · Short answer*

(b) (i) In a cross between violet flowered plants and white flowered plants, state the characteristics of the plants obtained in the $F_1$ progeny.
(ii) If the plants of $F_1$ progeny are self-pollinated, then what would be observed in the plants of $F_2$ progeny ?
(iii) If 100 plants are produced in $F_2$ progeny, then how many plants will show the recessive trait ?

**Part (i)**

1. All the plants obtained in the $F_1$ progeny will have violet flowers.
2. Violet flower colour is the dominant trait which expresses itself in the $F_1$ generation.

Answer (i): All plants obtained in the $F_1$ progeny have violet flowers.

**Part (ii)**

1. Self-pollination of $F_1$ plants results in both violet and white flowered plants in the $F_2$ progeny.
2. The observed phenotypic ratio is 3 violet flowered plants to 1 white flowered plant.

Answer (ii): Both violet and white flowered plants are observed in the ratio of 3:1.

**Part (iii)**

1. The proportion of plants showing the recessive white trait in the $F_2$ progeny is $\frac{1}{4}$.
2. Out of 100 plants, the number of plants showing the recessive trait is $\frac{1}{4} \times 100 = 25$.

Answer (iii): 25 plants will show the recessive trait.

**Answer:** In $F_1$ progeny all plants have violet flowers, in $F_2$ progeny the phenotypic ratio is 3 violet to 1 white, and 25 plants show the recessive trait out of 100.

> Common mistake: Confusing the $F_1$ progeny characteristics with $F_2$ progeny or miscalculating the number of recessive plants as 75 instead of 25.

### Question 14

*4 marks · Case-based*

The mechanism by which the sex of an individual is determined is called sex-determination. In human beings, sex of a newborn is genetically determined, whereas in some others it is not. There are 46 (23 pairs) chromosomes in human beings. Out of these, 44 (22 pairs) control the body characters and 2 (one pair) are known as sex chromosomes. The sex chromosomes are of two types — X chromosome and Y chromosome. At the time of fertilisation, depending upon which type of male gamete fuses with the female gamete, the sex of the newborn child is decided.
(a) Why is a pair of sex chromosomes in human beings called a mismatched pair in terms of type and size ?
(b) Out of male or female, which of them has a perfect pair of sex chromosomes ? In case of a perfect pair, will the gametes produced be of the same kind or of a different kind ?
(c) (i) Name two animals whose sex is not genetically determined. Explain the process of their sex determination.

**Part (a)**

1. Human males have one X and one Y chromosome.
2. The Y chromosome is much shorter and structurally different compared to the X chromosome, hence it is called a mismatched pair.

Answer (a): The XY pair is mismatched because the Y chromosome is significantly smaller than the X chromosome.

**Part (b)**

1. Human females have a perfect pair of sex chromosomes represented as XX.
2. Since both sex chromosomes are identical, all gametes produced by females are of the same kind containing an X chromosome.

Answer (b): Females have a perfect pair (XX), and the gametes produced are all of the same kind (carrying an X chromosome).

**Part (c)(i)**

1. Animals such as some reptiles (e.g., turtles and lizards) do not have genetically determined sex.
2. In these animals, the temperature at which fertilized eggs are kept determines whether the developing animal will be male or female.

Answer (c)(i): In some reptiles, sex is determined by environmental temperature rather than genetics.

**Answer:** Sex determination in humans depends on the inheritance of X and Y chromosomes from the male parent.

> Common mistake: Confusing male and female heterogamety or stating that temperature determines sex in all reptiles.

### Question 14 (OR)

*4 marks · Case-based*

The mechanism by which the sex of an individual is determined is called sex-determination. In human beings, sex of a newborn is genetically determined, whereas in some others it is not. There are 46 (23 pairs) chromosomes in human beings. Out of these, 44 (22 pairs) control the body characters and 2 (one pair) are known as sex chromosomes. The sex chromosomes are of two types — X chromosome and Y chromosome. At the time of fertilisation, depending upon which type of male gamete fuses with the female gamete, the sex of the newborn child is decided.
(a) Why is a pair of sex chromosomes in human beings called a mismatched pair in terms of type and size ?
(b) Out of male or female, which of them has a perfect pair of sex chromosomes ? In case of a perfect pair, will the gametes produced be of the same kind or of a different kind ?
(ii) With the help of a flowchart only, show how sex is genetically determined in human beings.

**Part (a)**

1. Human males possess one X and one Y chromosome which are unequal in size.
2. Due to this difference in size and type, the XY combination is referred to as a mismatched pair.

Answer (a): The XY pair is called mismatched because the Y chromosome is shorter than the X chromosome.

**Part (b)**

1. Human females possess a pair of X chromosomes (XX), which is a perfect pair.
2. The gametes (ova) produced by females are all of the same kind, each containing a single X chromosome.

Answer (b): Females have a perfect pair (XX) and produce gametes of the same kind.

**Part (ii)**

1. Parents: Parents (XX Female $\times$ XY Male)
2. Gametes: Female produces (X), Male produces (X) or (Y)
3. Offspring: Fusion of X sperm with X egg gives XX (Female), and fusion of Y sperm with X egg gives XY (Male).

Answer (ii): Flowchart showing equal probability of XX (female) and XY (male) offspring based on fertilising sperm.

**Answer:** Sex in human beings is genetically determined by the type of sperm (X or Y) that fuses with the egg (X).

> Common mistake: Omitting the chromosome types in the flowchart representation.

## Related pages

- [Heredity: NCERT solutions](https://www.swavid.com/science/class/10/chapter/heredity/ncert-solutions)
- [All CBSE Class 10 Science papers](https://www.swavid.com/cbse/class-10/science/previous-year-papers)

Solutions written by SwaVid, a personal AI tutor for Class 6 to 10 Maths and Science. Practise this chapter free: https://www.swavid.com/start/student