Important Questions for Class 10 Science Chapter 8: Heredity

Heredity is the process by which traits and characteristics are reliably passed from parents to offspring through genes. It explains why children resemble their parents and how variations arise across generations.

Important Questions Class 10 Science Chapter 8 on this page covers every concept from the NCERT 2026-27 book: accumulation of variation, inherited traits, Mendel's contributions, dominant and recessive traits, monohybrid and dihybrid inheritance, chromosomes, and sex determination. All heredity class 10 important questions are structured for board exam preparation, with answers written to match what CBSE expects at every mark level.

This chapter carries questions across all mark levels. A student who can draw a correct Punnett square for a monohybrid cross, explain why the father determines the sex of the child, and distinguish inherited from acquired traits will handle every format in this chapter. Start your chapter revision with Important Questions Class 10 Science Chapter 7 and build forward from there.

Key Takeaways: Heredity Class 10 Quick Revision

Introduction to Heredity Class 10

Reproduction produces individuals that are similar but not identical. Variations arise because DNA copying is not perfectly accurate. In asexual reproduction, variations are minor. In sexual reproduction, variations are much greater because each offspring inherits genetic material from two parents.

Not all variations have equal chances of surviving. Bacteria that can withstand heat survive better in a heatwave. This selection of variants by environmental conditions forms the basis of how populations change over time.

Chapter 8 focuses specifically on how traits are inherited: the mechanism behind heredity. The chapter opens with variation, moves through Mendel's pea plant experiments, and ends with the genetic basis of sex determination in human beings.

Accumulation of Variation During Reproduction: Important Questions

These heredity class 10 questions and answers on variation set up every concept that follows in the chapter. Variation is the reason heredity matters for species survival.

Q1 (1 mark): If a trait A exists in 10% of a population of an asexually reproducing species and trait B exists in 60% of the same population, which trait is likely to have arisen earlier? Trait B. A trait present in a larger percentage of the population has had more generations to accumulate and spread, so it arose earlier.

Q2 (1 mark): How do variations arise in asexually reproducing organisms? Variations in asexually reproducing organisms arise due to small inaccuracies during DNA copying. Each copying event introduces minor errors that create subtle differences between individuals.

Q3 (2 marks): How does the creation of variations in a species promote survival? Variations give different individuals different kinds of advantages. In a changing environment, those individuals with a beneficial variation survive better. For example, bacteria that can withstand heat survive in a heatwave while others die. Variation ensures that at least some individuals in a population can adapt to new conditions.

Q4 (2 marks): Why are variations more in sexually reproducing organisms than in asexually reproducing organisms? In asexual reproduction, only one parent contributes DNA, so variations arise only from DNA copying errors. In sexual reproduction, two parents contribute genetic material. The combination of genes from both parents creates much greater diversity in the offspring.

Inherited Traits: Class 10 Heredity Important Questions

These class 10 heredity important questions test the definitions and reasoning that carry 1-mark and 2-mark in board papers.

Q5 (1 mark): What are inherited traits? Give one example. Inherited traits are characteristics passed from parents to offspring through genes. Example: free or attached earlobes in human beings.

Q6 (1 mark): What is a gene? A gene is a section of DNA that provides information for making one protein in the cell. Genes control characteristics or traits in an organism.

Q7 (2 marks): Why does a child not look exactly like either parent? A child inherits genetic material from both parents: one copy of each gene from the mother and one from the father. The combination of these two sets creates a unique genetic makeup. Dominant and recessive interactions among these genes result in a child who shares features with both parents but is identical to neither.

Q8 (2 marks): How do both parents contribute equally to the genetic makeup of the child? During sexual reproduction, each parent contributes one germ cell. Each germ cell carries one set of genes. When two germ cells fuse during fertilisation, the child receives one complete gene set from the mother and one from the father. This ensures equal genetic contribution from both parents.

Mendel's Contributions: Heredity Important Questions Class 10

These heredity important questions class 10 cover Mendel's experiments, which are the most heavily tested topic in this chapter. Expect at least one question on Mendel in every CBSE 2026 board paper.

Q9 (1 mark): Who is called the Father of Genetics? Gregor Johann Mendel (1822-1884) is called the Father of Genetics.

Q10 (1 mark): Name the plant Mendel used for his experiments. Mendel used Pisum sativum (garden pea) for his experiments.

Q11 (2 marks): Why did Mendel choose pea plants for his experiments? Mendel chose pea plants because they have a short life cycle, allowing results to be collected quickly. They show clearly contrasting pairs of traits such as tall/short, round/wrinkled seeds, and violet/white flowers. The plants produce a large number of offspring, making statistical analysis reliable.

Q12 (2 marks): What are Mendelian factors? How many contrasting characters did Mendel observe in pea plants? Mendelian factors are hereditary units that carry a character from parents to offspring: now called genes. Mendel identified seven pairs of contrasting characters in pea plants, including seed shape (round/wrinkled), seed colour (yellow/green), flower colour (violet/white), and plant height (tall/short).

Q13 (3 marks): What is the significance of Mendel's work? State three laws of Mendel. Mendel was the first scientist to keep a mathematical count of individuals showing each trait across generations, which allowed him to discover the rules of inheritance.

Law of Dominance: When two different alleles of a trait are present in an organism, only the dominant one expresses itself. The recessive allele remains hidden.

Law of Segregation: During gamete formation, the two copies of a gene separate so each gamete receives only one copy. The two copies come back together at fertilisation.

Law of Independent Assortment: When two or more pairs of contrasting traits are inherited, each pair is inherited independently of the other pairs.

Dominant and Recessive Traits: Heredity Class 10 Important Questions

Q14 (1 mark): What is a dominant trait? A dominant trait is one that expresses itself even when only one copy is present. For example, tallness (T) in pea plants is dominant over shortness (t).

Q15 (1 mark): What is a recessive trait? Give one example. A recessive trait is one that expresses itself only when both copies of the gene are recessive. Example: shortness (tt) in pea plants.

Q16 (2 marks): When Mendel crossed a tall plant with a short plant, he got no medium-height plants in F1. Why? In the F1 generation, all plants were tall because tallness is dominant over shortness. The dominant allele T completely suppresses the recessive allele t. So even though the F1 plants carry both alleles (Tt), only the dominant trait is expressed. No intermediate height appears because dominance works on an all-or-nothing basis.

Q17 (2 marks): Give two recessive and two dominant traits of the garden pea.

Q18 (3 marks): A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this enough to say which trait is dominant? Why or why not? No, this information alone is not enough. Blood group is determined by a pair of genes: one from each parent. The father has blood group A, but if his genotype is AO (one A allele and one O allele), he can pass on the O allele to the child. The mother with blood group O has genotype OO and always passes O. We cannot determine dominance from this information alone because we do not know whether the A trait was received in a homozygous or heterozygous form.

Monohybrid Cross: Heredity Class 10 Important Questions

Monohybrid cross questions carry 3-mark and 5-mark marks in CBSE 2026 board papers. These important questions of heredity class 10 require both the Punnett square and the ratio to score full marks.

Q19 (1 mark): What is a monohybrid cross? A monohybrid cross is a cross between two plants that differ in only one pair of contrasting traits. The F2 phenotypic ratio is 3:1.

Q20 (1 mark): What is the phenotypic ratio of the F2 generation in a monohybrid cross? The phenotypic ratio in the F2 generation of a monohybrid cross is 3:1 (three dominant : one recessive).

Q21 (3 marks): Explain Mendel's monohybrid cross with a suitable diagram. Mendel crossed a tall pea plant (TT) with a short pea plant (tt).

P generation: TT x tt. F1 generation: All offspring are Tt — all tall. Only the dominant trait is expressed.

F1 x F1: Tt x Tt.

Result: TT (tall), Tt (tall), Tt (tall), tt (short). Phenotypic ratio = 3 tall : 1 short. Genotypic ratio = 1TT : 2Tt : 1tt.

This experiment shows that the recessive trait (shortness) was not lost in F1. It was hidden. It reappears in F2, proving that both alleles were inherited by F1 plants.

Q22 (5 marks): Mendel crossed a tall pea plant bearing violet flowers with a short pea plant bearing white flowers. The progeny all bore violet flowers but almost half were short. What does this suggest about the genetic makeup of the tall parent? The tall parent's genotype is TtWW. The fact that all F1 progeny bore violet flowers means violet is dominant and the tall parent contributed W in a homozygous form (WW): no white flowers appeared. The fact that almost half the progeny were short means the tall parent was heterozygous for height (Tt). The cross Tt x tt gives 50% tall (Tt) and 50% short (tt). This matches the observation.

Dihybrid Cross and Independent Inheritance: Heredity Class 10 Extra Questions

These heredity class 10 extra questions on dihybrid cross appear as 3-mark and 5-mark questions in CBSE 2026 board papers. The 9:3:3:1 ratio and independent assortment must both be explained in full for maximum marks.

Q23 (1 mark): What is a dihybrid cross? A dihybrid cross involves two pairs of contrasting traits. The F2 phenotypic ratio is 9:3:3:1.

Q24 (2 marks): What are the four phenotypes seen in F2 of a dihybrid cross between round yellow seeds and wrinkled green seeds? When RRyy (round, green) is crossed with rrYY (wrinkled, yellow), F1 is all RrYy (round, yellow). F2 phenotypes and ratio: Round, yellow (9); Round, green (3); Wrinkled, yellow (3); Wrinkled, green (1). Total ratio = 9:3:3:1.

The appearance of round green and wrinkled yellow in F2 (combinations not present in either parent) proves that the two traits are inherited independently.

Q25 (3 marks): How do Mendel's experiments show that traits are inherited independently? In Mendel's dihybrid cross, he crossed a round green seeded pea plant (RRyy) with a wrinkled yellow seeded plant (rrYY). All F1 plants had round yellow seeds (RrYy). When F1 plants self-pollinated, F2 plants showed four phenotypes in the ratio 9:3:3:1.

Two new combinations appeared (round green and wrinkled yellow) that were not present in either parent plant. This proves that the seed shape gene and seed colour gene assort independently during gamete formation. Their inheritance is not linked to each other.

How Traits Get Expressed: Genes, DNA and Proteins

Q26 (2 marks): How do genes control characteristics of an organism? Genes control characteristics through proteins. A section of DNA called a gene provides instructions for making one specific protein. That protein (often an enzyme) controls a biological process. For example, a gene controls how efficiently a plant makes the enzyme involved in producing the growth hormone, which determines whether the plant is tall or short.

Q27 (2 marks): Why must each germ cell have only one set of genes? Each germ cell must carry only one set of genes so that when two germ cells combine during fertilisation, the resulting zygote has exactly two sets of genes. If germ cells carried two sets, the zygote would have four sets, doubling with each generation and making the chromosome number unstable.

Q28 (2 marks): What is a chromosome? How does it help in independent inheritance of traits? A chromosome is a separate, independent piece of DNA that carries a set of genes. Genes for different traits are located on different chromosomes. They sort independently during germ cell formation. This physical separation of chromosomes is the mechanism behind Mendel's law of independent assortment.

Sex Determination in Human Beings: Heredity Class 10 Important Questions

Sex determination is a high-probability topic in CBSE 2026 board papers. These heredity class 10 questions and answers on sex determination appear as both 2-mark and 5-mark questions.

Q29 (1 mark): What are autosomes and sex chromosomes? Human cells have 23 pairs of chromosomes. 22 pairs are autosomes: identical in males and females. The 23rd pair is the sex chromosomes. Women have XX and men have XY.

Q30 (1 mark): How many autosomes are present in a human sperm? 22 autosomes are present in a human sperm, along with either an X or a Y sex chromosome.

Q31 (2 marks): How is the sex of the child determined in human beings? The sex of the child is determined by the father's sperm. All eggs from the mother carry one X chromosome. The father produces two types of sperm: half carry X and half carry Y. If a sperm carrying X fertilises the egg, the child is a girl (XX). If a sperm carrying Y fertilises the egg, the child is a boy (XY).

Q32 (3 marks): Explain sex determination in human beings with the help of a diagram.

Father (XY) produces two types of gametes: X-sperm and Y-sperm (50% each). Mother (XX) produces only one type of gamete: X-egg.

Probability of a girl = 50%; probability of a boy = 50%. The sex of the child is determined at the moment of fertilisation. It depends entirely on whether the father contributes an X or a Y chromosome.

Q33 (5 marks): Describe the full mechanism by which sex is determined in human beings. Why is the father responsible for the sex of the child? In human beings, sex is genetically determined by the sex chromosomes. Most human chromosomes exist as 22 matched pairs called autosomes. The 23rd pair is the sex chromosomes, which differ in males and females.

Females have two identical sex chromosomes, both called X (XX). Males have a mismatched pair: one normal-sized X and one short Y chromosome (XY).

During gamete formation, each germ cell receives one chromosome from each pair. The mother, being XX, always produces eggs carrying one X chromosome. The father, being XY, produces two types of sperm: 50% carry X and 50% carry Y.

When an X-bearing sperm fertilises the egg: XX = female child. When a Y-bearing sperm fertilises the egg: XY = male child.

Since the mother always contributes X and the father determines whether X or Y is passed on, the sex of the child is decided by the father's sperm. This is why the father is responsible for determining the sex of the child.

Heredity Class 10 PYQ: Board-Style Questions

These heredity class 10 pyq are based on the pattern of actual CBSE board questions from this chapter. Practising these heredity pyqs class 10 sets builds the exact format and length the examiner expects.

PYQ 1 (1 mark): A Mendelian experiment crossed tall plants (TT) with short plants (tt). What was the phenotype of all F1 plants? All F1 plants were tall (Tt). Tallness is dominant, so the dominant trait is expressed in all F1 offspring.

PYQ 2 (1 mark): What is the percentage possibility of a couple having a daughter? 50 percent. Half the father's sperm carry X and half carry Y. When X-bearing sperm fertilises the egg, a girl is born. The probability is equal for both sexes.

PYQ 3 (2 marks): A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. Can we say whether light eye colour is dominant or recessive? No. We cannot determine dominance from this information alone. Each parent contributes one copy of the eye colour gene. If both parents have light eyes, they may both be homozygous recessive. Cross-breeding between light-eyed and dark-eyed parents and observing F1 offspring would give clearer information.

PYQ 4 (3 marks): Two pink-coloured flowers on crossing give 1 red, 2 pink, and 1 white offspring. Explain the inheritance pattern. This is an example of incomplete dominance. Neither the red allele (R) nor the white allele (r) is fully dominant over the other. The heterozygous genotype Rr gives pink: a blended phenotype. The cross Rr x Rr gives: RR (red), Rr (pink), Rr (pink), rr (white). Phenotypic ratio = 1:2:1.

PYQ 5 (5 marks): Outline a project which aims to find the dominant coat colour in dogs. Select a pure-breeding male dog with a black coat (genotype BB) and a pure-breeding female dog with a brown coat (genotype bb). Cross them. Observe the coat colour of all F1 offspring. If all F1 pups are black, then black is dominant over brown. If all are brown, then brown is dominant.

To confirm, cross the F1 dogs with each other (Bb x Bb). If black is dominant, the F2 ratio should be 3 black : 1 brown. The colour that appears in 75% of F2 offspring is the dominant coat colour.

Heredity Class 10 Extra Questions and Answers

These heredity class 10 extra questions and answers go beyond the standard NCERT exercises. They appear in pre-board and CBSE 2026 school assessments.

Extra Q1 (2 marks): What is the difference between inherited and acquired traits?

Extra Q2 (2 marks): Why are acquired traits not inherited? Acquired traits are changes that happen in the non-reproductive tissues (somatic cells) of an organism during its lifetime. These changes do not alter the DNA in the germ cells. Since germ cells carry the genetic information passed to the next generation, traits that only affect body cells cannot be inherited.

Extra Q3 (2 marks): What is genotype and phenotype? The genotype is the actual genetic constitution of an organism: the specific alleles it carries (e.g. Tt, TT, tt). The phenotype is the physical expression of those genes (e.g. tall or short). Two organisms can have different genotypes (TT and Tt) but the same phenotype (both tall).

Extra Q4 (3 marks): If a round green seeded pea plant (RRyy) is crossed with a wrinkled yellow seeded plant (rrYY), what will the F1 seeds look like? What ratio will you see if F1 plants are self-pollinated? The F1 seeds will all be round and yellow (RrYy). Round seed (R) is dominant over wrinkled (r) and yellow (Y) is dominant over green (y). When F1 plants (RrYy) self-pollinate, the F2 ratio will be: Round yellow : Round green : Wrinkled yellow : Wrinkled green = 9:3:3:1.

Extra Q5 (3 marks): What is the significance of the 9:3:3:1 ratio? The 9:3:3:1 ratio appears in the F2 generation of a dihybrid cross. It proves that two different traits are inherited independently. The appearance of new trait combinations in F2 (round green and wrinkled yellow, absent in both parents and F1) demonstrates that genes for different traits are on separate chromosomes. This is the experimental basis of Mendel's Law of Independent Assortment.

Important Diagrams from Heredity Class 10

These are the three diagrams you must draw and label for CBSE 2026 board exams. CBSE awards marks specifically for correct labels and the Punnett square grid.

Diagram 1: Monohybrid Cross (Tall x Short) Show P generation → F1 (all Tt, all tall) → F1 x F1 → F2 (TT, Tt, Tt, tt; ratio 3 tall : 1 short).

Diagram 2: Dihybrid Cross (Round Green x Wrinkled Yellow) Show P generation → F1 (all RrYy, all round yellow) → F1 x F1 → F2 Punnett square showing 9:3:3:1 ratio.

Diagram 3: Sex Determination in Human Beings Show father (XY) producing X-sperm and Y-sperm. Mother (XX) producing only X-eggs. Show XX = female, XY = male. Label gametes, zygotes, and offspring sex.

Class 10 Heredity Important Topics for Quick Revision

These important questions from heredity class 10 are most likely to appear in CBSE 2026 board papers. Use this list as your final revision checklist.

Variation during reproduction: why it happens and its significance. Mendel's experiment: what he did, what he found, and what it means. Dominant and recessive traits: definition and how to identify from a cross. Monohybrid cross: Punnett square, phenotypic ratio 3:1, genotypic ratio 1:2:1. Dihybrid cross: Punnett square, phenotypic ratio 9:3:3:1, independent assortment. How genes express traits: through proteins and enzymes. Chromosomes: role in carrying genes and enabling independent assortment. Sex determination: XX female, XY male, role of father's sperm.

Marks distribution (approximate): 1-mark questions: definitions of heredity, gene, dominant/recessive trait, genotype, phenotype. 2-mark questions: difference between inherited and acquired traits, sex determination explanation, why acquired traits are not inherited. 3-mark questions: Mendel's experiment, monohybrid cross diagram, sex determination diagram. 5-mark questions: full dihybrid cross with Punnett square, complete explanation of sex determination.