THE BUSY BRAINS • BY MANSI SARASWAT
HEREDITY
Class 10 Science | Important Questions with Answers
Pre-Board & Board Exam Preparation
| NCERT-Based Questions | Mendel | Genetics | MCQs | Case-Based Questions
Class 10 Science Heredity is an important chapter for understanding how traits are passed from parents to offspring and how variations arise during reproduction. This chapter explains the basic principles of inheritance, genes, traits, chromosomes and variation.
This comprehensive Class 10 Heredity Important Questions with Answers resource is designed for CBSE Pre-Board and Board Exam preparation. It covers NCERT-based questions on Mendel's experiments, dominant and recessive traits, inheritance of traits, independent inheritance, gene expression, chromosomes and sex determination in human beings.
Students should especially practise Mendel's monohybrid cross, dihybrid cross, dominant and recessive traits, genotype and phenotype, inheritance of two traits, gene expression and the XX-XY mechanism of sex determination.
The questions below are structured for quick revision as well as detailed Board Exam preparation and include important questions, NCERT questions, MCQs, case-based questions and exam-focused revision points.
MUST DO
Mendel's Experiments, Dominant & Recessive Traits, Monohybrid Cross & Sex Determination
VERY IMPORTANT
Genes, DNA, Chromosomes, Independent Inheritance & Gene Expression
PRACTICE
Genetic Crosses, MCQs, Case-Based Questions & NCERT Exercise Questions
⭐ Board Exam Focus:
Do not only memorise Mendel's ratios. Understand the
cross, genotype, phenotype, dominant/recessive nature
and reasoning behind the result.
1. Variation During Reproduction
MUST DO
Q1. What is variation?
Answer:
Variation refers to the differences that arise among individuals
of the same species.
During reproduction, offspring may resemble their parents but may
also show small differences.
Q2. Why are variations produced during reproduction?
Answer:
Variations can arise because of small inaccuracies during DNA copying.
In sexual reproduction, genetic material from two parents also
contributes to greater diversity.
VERY IMPORTANT
Q3. How does sexual reproduction produce more variation than asexual reproduction?
In asexual reproduction, a single parent contributes genetic material,
so the offspring are generally very similar, apart from variations
arising during DNA copying.
In sexual reproduction, genetic material from two parents combines.
This produces greater diversity among offspring.
Q4. Are all variations equally useful for survival?
Answer:
No. Different variations provide different advantages or disadvantages
depending on the environment.
For example, bacteria that can withstand high temperatures are more
likely to survive during a heat wave.
PRACTICE
Q5. If trait A exists in 10% of a population and trait B exists in 60% of the same asexually reproducing population, which trait is likely to have arisen earlier?
Answer:
Trait B is likely to have arisen earlier because it is present in a
larger proportion of the population.
If the population has been reproducing asexually, a variation that
arose earlier would have had more opportunities to be passed on
through successive generations.
Q6. How does creation of variations in a species promote survival?
Variations increase the diversity within a population.
If environmental conditions change, some variations may help
individuals survive better. These individuals may reproduce and pass
the useful variation to the next generation.
Thus, variation can increase the chances of survival of a species.
2. Heredity and Inherited Traits
MUST DO
Q7. What is heredity?
Answer:
Heredity is the process by which traits and characteristics are
passed from parents to offspring.
The rules of heredity determine how traits are reliably inherited.
Q8. What are inherited traits?
Inherited traits are characteristics passed from parents to their
offspring through genetic material.
Examples include certain features that contribute to similarities
between parents and offspring.
Q9. Why does a child resemble its parents but not look exactly like them?
A child receives genetic material from both parents.
Therefore, the child inherits many characteristics from the parents,
but the particular combination of inherited genetic material can
produce differences and variations.
VERY IMPORTANT
Q10. How much genetic material does a child receive from each parent?
During sexual reproduction, the father and mother contribute
practically equal amounts of genetic material to the child.
This means that both parents contribute to the traits of the offspring.
Q11. What are the two versions of a gene controlling a trait in a sexually reproducing organism?
For each trait, an individual generally has two copies of the
corresponding gene—one inherited from each parent.
The two copies may be identical or different.
3. Mendel's Experiments and Contributions
MUST DO
Q12. Who was Gregor Johann Mendel?
Gregor Johann Mendel was a scientist who studied inheritance using
garden pea plants.
He selected contrasting visible characteristics and carefully counted
individuals showing particular traits in each generation.
His work helped establish important rules of inheritance.
Q13. Why did Mendel select pea plants for his experiments?
Mendel used pea plants because they showed clear contrasting
characteristics such as:
- Tall and short plants
- Round and wrinkled seeds
- White and violet flowers
Q14. What was special about Mendel's experimental method?
Mendel counted the number of individuals showing particular traits
in each generation and used the resulting numerical patterns to
arrive at rules of inheritance.
VERY IMPORTANT
Q15. What happened when Mendel crossed a tall pea plant with a short pea plant?
The first-generation, or F1, progeny were all tall.
There were no medium-height plants.
This showed that one parental trait was expressed while the other
was not expressed in the F1 generation.
Q16. What happened when the F1 tall plants were allowed to self-pollinate?
The second-generation, or F2, progeny were not all tall.
Approximately one-quarter of the F2 plants were short.
Thus, both tallness and shortness had been inherited in the F1
generation, although only tallness was expressed.
Q17. What did Mendel propose about the factors controlling traits?
Mendel proposed that two copies of the factor controlling a trait
are present in sexually reproducing organisms.
These two copies may be identical or different.
These factors are now called genes.
4. Dominant and Recessive Traits
MUST DO
Q18. What is a dominant trait?
A trait that is expressed even when only one copy of the corresponding
gene is present is called a dominant trait.
For example, in Mendel's pea plant experiment, tallness was dominant
over shortness.
Q19. What is a recessive trait?
A trait that is expressed only when both copies of the corresponding
gene are recessive is called a recessive trait.
In Mendel's tall/short pea plant example, shortness was recessive.
Q20. Differentiate between dominant and recessive traits.
| Dominant Trait | Recessive Trait |
|---|---|
| Expressed when one copy is sufficient. | Expressed when both copies are recessive. |
| Represented by a capital letter in simple genetic crosses. | Represented by a small letter. |
| Example: T for tallness. | Example: t for shortness. |
Q21. What do TT, Tt and tt represent?
- TT: Two copies of the dominant factor.
- Tt: One dominant and one recessive copy.
- tt: Two copies of the recessive factor.
5. Monohybrid Inheritance
MUST DO
Q22. Explain Mendel's monohybrid cross using tall and short pea plants.
Let:
T = tall
t = short
Parental cross: TT × tt
The gametes are: T from the tall parent and t from the short parent. Therefore, all F1 offspring are: Tt Since T is dominant, all F1 plants are tall.
t = short
Parental cross: TT × tt
The gametes are: T from the tall parent and t from the short parent. Therefore, all F1 offspring are: Tt Since T is dominant, all F1 plants are tall.
| t | t | |
|---|---|---|
| T | Tt | Tt |
| T | Tt | Tt |
Q23. What happens when F1 plants are self-pollinated?
The F1 plants are:
Tt × Tt
The possible combinations are:
Thus:
Genotypic ratio = 1 TT : 2 Tt : 1 tt
Phenotypic ratio = 3 Tall : 1 Short
| T | t | |
|---|---|---|
| T | TT | Tt |
| t | Tt | tt |
Phenotypic ratio = 3 Tall : 1 Short
VERY IMPORTANT
Q24. What is the phenotypic ratio obtained in Mendel's monohybrid cross?
The phenotypic ratio in the F2 generation is:
3 : 1
That is:
3 tall : 1 short
Q25. What is the genotypic ratio in the F2 generation of a monohybrid cross?
The genotypic ratio is:
1 : 2 : 1
That is:
1 TT : 2 Tt : 1 tt
6. Independent Inheritance of Two Traits
MUST DO
Q26. What is independent inheritance?
Independent inheritance means that different traits can be inherited
separately.
Mendel's experiments showed that the tall/short trait and
round/wrinkled seed trait were independently inherited.
Q27. What happened when Mendel studied two traits together?
Mendel studied two characteristics at the same time, such as plant
height and seed shape.
The F2 generation showed not only parental combinations but also
new combinations of traits.
For example, tall plants with wrinkled seeds and short plants with
round seeds could appear.
VERY IMPORTANT
Q28. What new combinations of traits can arise during independent inheritance?
When two traits are inherited independently, new combinations may
appear in the offspring.
For the traits studied by Mendel, the F2 generation could contain:
- Tall plants with round seeds
- Tall plants with wrinkled seeds
- Short plants with round seeds
- Short plants with wrinkled seeds
Q29. What phenotypic ratio was obtained in Mendel's dihybrid experiment?
The classic phenotypic ratio shown by the experiment was:
9 : 3 : 3 : 1
The chapter's experimental data show:
- 315 round, yellow
- 108 round, green
- 101 wrinkled, yellow
- 32 wrinkled, green
7. How Do Genes Control Traits?
MUST DO
Q30. What is a gene?
A gene is a section of DNA that provides information for making
a particular protein.
Genes therefore provide information that contributes to the
expression of traits.
Q31. How does DNA control characteristics or traits?
DNA contains information for making proteins.
These proteins can influence processes in the organism and thereby
affect characteristics or traits.
For example, the chapter explains plant height through the production
of a plant hormone and the efficiency of an enzyme involved in
that process.
Q32. How can a change in a gene affect plant height?
Suppose a gene controls an enzyme needed for making a plant hormone.
If the enzyme works efficiently, more hormone is produced and the
plant can become tall.
If a change makes the enzyme less efficient, less hormone is produced
and the plant can become short.
Thus, genes control characteristics through their role in protein
production and cellular processes.
8. Genes, DNA and Chromosomes
VERY IMPORTANT
Q33. What are chromosomes?
Chromosomes are separate pieces of DNA that carry genes.
The chapter explains that each gene set is present as separate
independent pieces, each called a chromosome.
Q34. How many copies of each chromosome are present in body cells?
In the context of the chapter, body cells have two copies of each
chromosome, one inherited from the male parent and one from the
female parent.
Q35. Why do germ cells have only one set of chromosomes?
Each germ cell receives one chromosome from each pair.
When two germ cells combine during sexual reproduction, the normal
number of chromosomes is restored in the offspring.
This helps maintain the stability of the DNA of the species.
MUST DO
Q36. How is equal genetic contribution of male and female parents ensured?
The body cells contain two copies of each chromosome.
During formation of germ cells, each germ cell receives only one
chromosome from each pair.
When male and female germ cells combine, one set comes from each
parent. Therefore, the offspring receives practically equal genetic
contributions from both parents.
9. Sex Determination in Human Beings
MUST DO
Q37. What are sex chromosomes?
The pair of chromosomes involved in determining sex is called the
sex chromosome pair.
In humans:
- Females have XX chromosomes.
- Males have XY chromosomes.
Q38. How is the sex of a child determined in human beings?
The mother has XX chromosomes and therefore all her eggs carry
an X chromosome.
The father has XY chromosomes and produces two types of sperm:
If a Y-bearing sperm fertilises the egg: XY → boy
- X-bearing sperm
- Y-bearing sperm
If a Y-bearing sperm fertilises the egg: XY → boy
| Mother X | Mother X | |
|---|---|---|
| Father X | XX | XX |
| Father Y | XY | XY |
VERY IMPORTANT
Q39. What is the probability of a child being a boy or a girl according to the XX-XY mechanism?
According to the inheritance pattern described in the chapter:
- Probability of XX child = 1/2
- Probability of XY child = 1/2
50% girls : 50% boys
Q40. Why is the father responsible for determining the sex of the child in humans?
The mother has XX chromosomes and therefore contributes only an
X chromosome through her egg.
The father has XY chromosomes and can contribute either X or Y
through his sperm.
Therefore:
X from father + X from mother = XX
Y from father + X from mother = XY
Y from father + X from mother = XY
Q41. Can environmental factors determine sex in all organisms?
No.
Different species use different mechanisms.
The chapter gives examples in which environmental factors such as
temperature can influence sex, while in human beings sex is largely
genetically determined.
10. NCERT-Based Important Questions
Q42. How do Mendel's experiments show that traits may be dominant or recessive?
Mendel crossed tall and short pea plants.
All plants in the F1 generation were tall, showing that tallness was
expressed while shortness was not expressed.
When F1 plants were self-pollinated, short plants appeared in the
F2 generation.
Therefore, tallness behaved as a dominant trait and shortness as
a recessive trait.
Q43. How do Mendel's experiments show that traits are inherited independently?
When Mendel studied two characteristics together, new combinations
appeared in the F2 generation.
For example, tall plants with wrinkled seeds and short plants with
round seeds appeared.
This showed that the two traits could be inherited independently.
PRACTICE
Q44. A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell which trait is dominant? Why?
No.
The observation of one family alone is not sufficient to establish
whether a trait is dominant or recessive.
The inheritance pattern depends on the genetic combinations involved.
Therefore, additional genetic information and appropriate crosses
would be needed.
Q45. How is the sex of the child determined in human beings?
The mother contributes an X chromosome through the egg.
The father contributes either X or Y through the sperm.
Therefore:
- X + X = XX → female child
- X + Y = XY → male child
Q46. A Mendelian experiment involved tall pea plants with violet flowers and short pea plants with white flowers. The progeny all had violet flowers but almost half were short. What is the genetic make-up of the tall parent?
Answer: TtWW
Therefore, the correct option is:
(c) TtWW
The tall parent must carry a recessive allele for height because
almost half of the progeny are short, while the violet-flower trait
is expressed in all progeny.
Q47. Children with light-coloured eyes are likely to have parents with light-coloured eyes. Can we conclude whether light eye colour is dominant or recessive?
No.
Simply observing that children resemble their parents is not enough
to determine whether the trait is dominant or recessive.
The inheritance pattern and appropriate genetic crosses would need
to be considered.
Q48. Outline a project to find the dominant coat colour in dogs.
A suitable project could involve:
- Identify dogs showing contrasting coat colours.
- Record the coat colour of parents and offspring over several generations.
- Select controlled crosses between dogs showing contrasting traits, where ethically and practically appropriate.
- Record the number of offspring showing each coat colour.
- Compare the observed inheritance patterns with expected Mendelian patterns.
- The trait consistently expressed in appropriate heterozygous combinations can be investigated as the possible dominant trait.
Q49. How is the equal genetic contribution of male and female parents ensured in the progeny?
Each parent contributes one chromosome from each chromosome pair
through the germ cell.
When the male and female germ cells combine, one set of chromosomes
comes from each parent.
Thus, the offspring receives practically equal genetic contributions
from both parents.
11. Important MCQs – Heredity Class 10
Q50. Which scientist is associated with the pea plant experiments on inheritance?
(a) Charles Darwin
(b) Gregor Mendel
(c) Robert Hooke
(d) Louis Pasteur
(a) Charles Darwin
(b) Gregor Mendel
(c) Robert Hooke
(d) Louis Pasteur
✔ Answer: (b) Gregor Mendel
Q51. In Mendel's tall and short pea plant experiment, all F1 plants were:
(a) Short
(b) Medium height
(c) Tall
(d) Half tall and half short
(a) Short
(b) Medium height
(c) Tall
(d) Half tall and half short
✔ Answer: (c) Tall
Q52. The F2 phenotypic ratio in a simple monohybrid cross is:
(a) 1:1
(b) 2:1
(c) 3:1
(d) 9:3:3:1
(a) 1:1
(b) 2:1
(c) 3:1
(d) 9:3:3:1
✔ Answer: (c) 3:1
Q53. The genotypic ratio in a Tt × Tt cross is:
(a) 3:1
(b) 1:1
(c) 1:2:1
(d) 9:3:3:1
(a) 3:1
(b) 1:1
(c) 1:2:1
(d) 9:3:3:1
✔ Answer: (c) 1:2:1
Q54. A trait expressed when only one copy of the corresponding gene is present is called:
(a) Recessive
(b) Dominant
(c) Acquired
(d) Environmental
(a) Recessive
(b) Dominant
(c) Acquired
(d) Environmental
✔ Answer: (b) Dominant
Q55. A section of DNA providing information for one protein is called:
(a) Cell
(b) Chromosome
(c) Gene
(d) Tissue
(a) Cell
(b) Chromosome
(c) Gene
(d) Tissue
✔ Answer: (c) Gene
Q56. Which chromosomes are present in a human female?
(a) XY
(b) XX
(c) YY
(d) XO
(a) XY
(b) XX
(c) YY
(d) XO
✔ Answer: (b) XX
Q57. Which chromosomes are present in a human male?
(a) XX
(b) XY
(c) YY
(d) XO
(a) XX
(b) XY
(c) YY
(d) XO
✔ Answer: (b) XY
Q58. Which chromosome can be contributed by the father to determine an XY child?
(a) X
(b) Y
(c) Both X and Y simultaneously
(d) None
(a) X
(b) Y
(c) Both X and Y simultaneously
(d) None
✔ Answer: (b) Y
Q59. Which process can produce greater diversity according to the chapter?
(a) Sexual reproduction
(b) Only binary fission
(c) No reproduction
(d) None
(a) Sexual reproduction
(b) Only binary fission
(c) No reproduction
(d) None
✔ Answer: (a) Sexual reproduction
Q60. The classic phenotypic ratio associated with Mendel's two-trait inheritance experiment is:
(a) 3:1
(b) 1:2:1
(c) 9:3:3:1
(d) 1:1
(a) 3:1
(b) 1:2:1
(c) 9:3:3:1
(d) 1:1
✔ Answer: (c) 9:3:3:1
12. Case-Based Questions – Board Exam Practice
Case Study 1 – Mendel's Monohybrid Cross
Mendel crossed a tall pea plant with a short pea plant. All plants in the F1 generation were tall. When the F1 plants were self-pollinated, short plants appeared in the F2 generation.
Q1. Which trait is dominant?
Q2. Which trait is recessive?
Q3. What is the expected phenotypic ratio in F2?
Q4. What is the genotypic ratio in F2?
Answers:
1. Tallness is dominant.
2. Shortness is recessive.
3. Phenotypic ratio = 3:1.
4. Genotypic ratio = 1:2:1.
1. Tallness is dominant.
2. Shortness is recessive.
3. Phenotypic ratio = 3:1.
4. Genotypic ratio = 1:2:1.
Case Study 2 – Independent Inheritance
Mendel studied two characteristics of pea plants together. In the F2 generation, new combinations of characteristics appeared in addition to the parental combinations.
Q1. What does this demonstrate?
Q2. Give one example of a new combination.
Q3. What is the classic F2 ratio associated with this experiment?
Answers:
1. It demonstrates independent inheritance of traits.
2. Tall plants with wrinkled seeds or short plants with round seeds.
3. 9:3:3:1.
1. It demonstrates independent inheritance of traits.
2. Tall plants with wrinkled seeds or short plants with round seeds.
3. 9:3:3:1.
Case Study 3 – Gene Expression
A gene provides information for a protein. Suppose the protein is an enzyme involved in the production of a plant hormone. If the enzyme works efficiently, more hormone is produced and the plant becomes tall. If the enzyme is less efficient, less hormone is produced and the plant may be short.
Q1. What does the gene provide information for?
Q2. How can a gene alteration affect plant height?
Q3. What is the relationship between genes and traits?
Answers:
1. It provides information for making a protein.
2. It can alter the efficiency of the enzyme and therefore affect the amount of hormone produced.
3. Genes control characteristics or traits through their role in protein production and cellular processes.
1. It provides information for making a protein.
2. It can alter the efficiency of the enzyme and therefore affect the amount of hormone produced.
3. Genes control characteristics or traits through their role in protein production and cellular processes.
Case Study 4 – Sex Determination in Humans
A human female has XX chromosomes while a human male has XY chromosomes. The egg always carries X, while sperm may carry either X or Y.
Q1. What chromosome does every egg carry?
Q2. What chromosomes can sperm carry?
Q3. What combination results in an XX child?
Q4. What combination results in an XY child?
Answers:
1. X.
2. X or Y.
3. X from mother + X from father = XX.
4. X from mother + Y from father = XY.
1. X.
2. X or Y.
3. X from mother + X from father = XX.
4. X from mother + Y from father = XY.
13. Quick Revision – Heredity Class 10
| Concept | Key Point |
|---|---|
| Variation | Differences among individuals of the same species. |
| Heredity | Transmission of traits from parents to offspring. |
| Gene | Section of DNA providing information for a protein. |
| Dominant trait | Trait expressed when one copy is sufficient. |
| Recessive trait | Trait expressed when both copies are recessive. |
| Monohybrid F2 phenotype | 3 : 1 |
| Monohybrid F2 genotype | 1 : 2 : 1 |
| Dihybrid phenotype | 9 : 3 : 3 : 1 |
| Female chromosomes | XX |
| Male chromosomes | XY |
| XX offspring | Female |
| XY offspring | Male |
⭐ Remember:
Monohybrid: 3:1 phenotype, 1:2:1 genotype
Dihybrid: 9:3:3:1 phenotype
Female: XX
Male: XY
Father's sperm: X or Y
Mother's egg: X
Monohybrid: 3:1 phenotype, 1:2:1 genotype
Dihybrid: 9:3:3:1 phenotype
Female: XX
Male: XY
Father's sperm: X or Y
Mother's egg: X
14. Class 10 Board Exam Final Checklist
- ☑ Learn the definition of heredity and variation.
- ☑ Understand why sexual reproduction creates greater variation.
- ☑ Learn Mendel's pea plant experiment.
- ☑ Understand the F1 and F2 generations.
- ☑ Memorise dominant and recessive traits.
- ☑ Practise TT × tt.
- ☑ Practise Tt × Tt.
- ☑ Learn 3:1 phenotypic ratio.
- ☑ Learn 1:2:1 genotypic ratio.
- ☑ Understand independent inheritance.
- ☑ Learn the 9:3:3:1 ratio.
- ☑ Understand genes and DNA.
- ☑ Understand the role of proteins in expression of traits.
- ☑ Learn the relationship between genes and chromosomes.
- ☑ Understand why germ cells contain one chromosome from each pair.
- ☑ Learn XX-XY sex determination.
- ☑ Practise NCERT in-text questions.
- ☑ Practise all four NCERT exercise questions.
- ☑ Practise MCQs and case-based questions.
15. Exam Strategy for Heredity
How to score better in this chapter?
1. Draw genetic crosses neatly.
Always write the parental generation, gametes, F1/F2 generation and final ratio clearly.
2. Do not confuse genotype and phenotype.
Genotype refers to the genetic combination, whereas phenotype refers to the expressed characteristic.
3. Remember the important ratios.
3:1 → monohybrid phenotype
1:2:1 → monohybrid genotype
9:3:3:1 → classic dihybrid phenotype
4. Learn the XX-XY cross.
This is a high-priority concept for questions on human sex determination.
5. Use scientific keywords.
Important terms include: variation, heredity, gene, DNA, chromosome, dominant, recessive, genotype, phenotype, independent inheritance, germ cell, XX and XY.
Always write the parental generation, gametes, F1/F2 generation and final ratio clearly.
2. Do not confuse genotype and phenotype.
Genotype refers to the genetic combination, whereas phenotype refers to the expressed characteristic.
3. Remember the important ratios.
3:1 → monohybrid phenotype
1:2:1 → monohybrid genotype
9:3:3:1 → classic dihybrid phenotype
4. Learn the XX-XY cross.
This is a high-priority concept for questions on human sex determination.
5. Use scientific keywords.
Important terms include: variation, heredity, gene, DNA, chromosome, dominant, recessive, genotype, phenotype, independent inheritance, germ cell, XX and XY.
🎯 Learn Heredity. Practise Genetics. Score Better.
Revise Class 10 Science Heredity with NCERT-based important questions, Mendelian crosses, MCQs, case-based questions and Board Exam revision notes.
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