Class 10 Science · Chapter 8

Heredity

120 Class 10 Science questions on Heredity from the NCERT textbook, NCERT Exemplar and CBSE board papers 2024–2026, each with its answer and a step-by-step solution.

CBSE Class 10 Science previous year papers, with answers →

Questions · page 5 of 6

1. Q81 CBSE 2026
   Show the cross ​and ​observations made by Mendel when ​he ​crossed pure tall pea plant ​with a pure short pea ​plant to get ${\text{F}}_1$ progeny.
   Show answer

   The cross $TT\times tt$ gives all-tall $Tt$ plants in ${\text{F}}_1$; tallness is dominant, shortness is recessive, and the traits do not blend.

   Cross: Parents: pure tall ($\text{TT}$) $\times$ pure short ($\text{tt}$). Gametes: $\text{T}$ from the tall parent and $\text{t}$ from the short parent. ${\text{F}}_1$ progeny: $\text{Tt}$, all tall. Observations: (1) All the ${\text{F}}_1$ plants were tall. (2) No plant was short or of medium height, so the traits did not blend. (3) Only one parental trait, tallness, was expressed: tallness is dominant and shortness is recessive (present but hidden in the ${\text{F}}_1$).

   Step-by-step solution →
2. Q82 CBSE 2026
   1. (a)Show a cross between a pea plant having round ​& green seed with a pea plant having ​wrinkled and yellow seeds ​upto ${\text{F}}_2$ ​generation.
   2. (b)Also write ​down ​results ​of ${\text{F}}_2$ generation.
   Show answer

   $F_1$ is all round yellow ($RrYy$); $F_2$ gives round yellow : round green : wrinkled yellow : wrinkled green $=9:3:3:1$.

   (a) Round ($R$) is dominant over wrinkled ($r$) and yellow ($Y$) over green ($y$), so the parents are $RRyy$ (round, green) and $rrYY$ (wrinkled, yellow). Their only gametes are $Ry$ and $rY$, so the whole $F_1$ is $RrYy$ and bears round, yellow seeds. Selfing the $F_1$ ($RrYy\times RrYy$) gives the four gametes $RY$, $Ry$, $rY$ and $ry$ from each side, and the $4\times 4$ Punnett square of $F_2$ holds $16$ combinations, row by row (gametes $RY$, $Ry$, $rY$, $ry$ along both sides): $RRYY$, $RRYy$, $RrYY$, $RrYy$; $RRYy$, $RRyy$, $RrYy$, $Rryy$; $RrYY$, $RrYy$, $rrYY$, $rrYy$; $RrYy$, $Rryy$, $rrYy$, $rryy$. (b) The $F_2$ generation gives four kinds of seed in the ratio $9:3:3:1$ — $9$ round yellow, $3$ round green, $3$ wrinkled yellow and $1$ wrinkled green out of every $16$. The parental combinations round-green and wrinkled-yellow reappear, and the new combinations round-yellow and wrinkled-green appear as well, which shows that seed shape and seed colour are inherited independently of each other.

   Step-by-step solution →
3. Q83 CBSE 2026
   “Each organism ​has two sets of ​all genes, one inherited from each parent i.e. both parents contribute equally to the DNA of the progeny during sexual reproduction”. If ​such is the case, then how is ​the ​stability of DNA of the species ensured ? ​Discuss.
   Show answer

   Gametes get half the chromosomes (one set), and fertilisation restores the full number ($23+23=46$), so the DNA of the species stays stable.

   If both parents really passed on the two sets of genes each of them carries, the progeny would have four sets, the next generation eight, and the amount of DNA would double in every generation. This does not happen, because sexual reproduction includes a halving step. Each body cell has two copies of each chromosome, one from the male parent and the other from the female parent. When germ cells are formed, each germ cell (gamete) takes only one chromosome from each pair, which may be of either maternal or paternal origin, so a gamete carries one set of genes instead of two and half the number of chromosomes; in human beings a body cell has 46 chromosomes (23 pairs) while a sperm or an egg has 23. When two germ cells unite at fertilisation, the zygote once again has two copies of each chromosome, 23 plus 23 giving 46, so the normal number of chromosomes is restored in the progeny. This re-establishment of the number of chromosomes, and so of the amount of DNA, in every generation ensures the stability of the DNA of the species.

   Step-by-step solution →
4. Q84 CBSE 2026
   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 ${\text{F}}_1$ generation. Answer the following ​questions ​:

   1. (a)Why only tall pea plants were observed in ${\text{F}}_1$ progeny ?[1]
   2. (b)By which method did Mendel obtain ${\text{F}}_2$ progeny ?[1]
   3. (c)(i)Write one difference between dominant and recessive trait.[2]
   4. (c)(ii)OR : Write two observations made by Mendel about ${\text{F}}_1$ progeny.[2]
   Show answer

   Tallness is dominant, so all ${\text{F}}_1$ are $\text{Tt}$ and tall; self-pollination gives ${\text{F}}_2$ in the ratio $3:1$; a recessive trait needs two factors.

   (a) Tallness is dominant over shortness. Every ${\text{F}}_1$ plant received $\text{T}$ from the tall parent and $\text{t}$ from the short parent, so all were $\text{Tt}$; in $\text{Tt}$ the dominant $\text{T}$ is expressed and $\text{t}$ is masked, so all were tall. (b) By self-pollination of the ${\text{F}}_1$ tall plants ($\text{Tt}\times \text{Tt}$), which gave tall and short plants in the ratio $3:1$ in the ${\text{F}}_2$. (c)(i) A dominant trait is expressed even when only one factor for it is present ($\text{Tt}$), so it appears in the ${\text{F}}_1$; a recessive trait is expressed only when both factors are recessive ($\text{tt}$), so it is hidden in the ${\text{F}}_1$ and reappears in the ${\text{F}}_2$. OR (c)(ii) All the ${\text{F}}_1$ plants were tall, showing the trait of only one parent; and none was short or of medium height, so the parental traits did not blend.

   Step-by-step solution →
5. Q85 CBSE 2026
   Read the following passage and ​answer the questions that follow : Indian scientists helped crack the DNA ​code of ‘bread-wheat’ genome, which would help ​improve global food security. It ​will allow faster breeding for climate-resilient varieties with drought, heat and frost tolerance, disease-resistant and superior quality ​grain. It may also help people suffering from allergy to ​wheat gluten. The information generated will help identify genes controlling yield, ​grain quality, resistance to diseases, etc. A variety of grains can thus ​be produced.

   1. (a)Write the full form of DNA.[1]
   2. (b)What type of cell division is involved in the formation of gametes ?[1]
   3. (c)(i)Variations confer an advantage to an individual to survive. Justify.[2]
   4. (c)(ii)OR : How do genes control characteristics or traits ?[2]
   Show answer

   DNA is deoxyribonucleic acid; meiosis forms gametes; suitable variations help survival; genes control traits by controlling protein synthesis.

   (a) DNA is deoxyribonucleic acid. (b) Meiosis, the reduction division: each gamete receives half the number of chromosomes of the parent cell, so the full number is restored when two gametes fuse at fertilisation. (c)(i) Individuals of a species are not all alike, and these differences are variations; depending on its nature, a variation suits its carrier to particular conditions. India has a variety of climatic conditions, so variations among wheat varieties, such as drought, heat or frost tolerance and disease resistance, let farmers grow the variety best suited to the climate of each region, which gives the benefit of survival and better grain quality. In the same way, when the surroundings change, for example a sudden rise in temperature, a population of bacteria is mostly killed, but the few with a heat-resistant variation survive and multiply. A variation therefore gives the individual that carries it a better chance of survival, and it is the basis of evolution. OR (c)(ii) Traits are brought about by proteins, and each protein is made according to the information in a gene, which is a section of DNA. For example, the height of a plant depends on the amount of a plant hormone it makes; the amount of that hormone depends on the efficiency of the enzyme that produces it, and an enzyme is a protein. The gene coding for that enzyme therefore decides how much hormone is made and so how tall the plant grows. If the gene is altered, a less efficient enzyme is made, less hormone is produced and the plant is short. Genes thus control characteristics by controlling the synthesis of proteins.

   Step-by-step solution →
6. Q86 CBSE 2025
   A tall ​pea ​plant with round seeds (TTRR) is ​crossed with a short pea plant ​with ​wrinkled ​seeds (ttrr). The $F_1$ ​generation will be

   1. (a)25% tall with round seeds
   2. (b)50% tall with wrinkled seeds
   3. (c)75% tall with wrinkled seeds
   4. (d)100% tall with round seeds
   Show answer

   (d) 100% tall with round seeds

   Step-by-step solution →
7. Q87 CBSE 2025
   Mendel ​obtained ${\text{F}}_2$ ​generation by

   1. (a)self pollinating ${\text{F}}_1$ generation plants
   2. (b)cross pollinating ${\text{F}}_1$ generation plants with plants having dominant trait.
   3. (c)cross pollinating ${\text{F}}_1$ generation plants with plants having recessive trait.
   4. (d)cross pollinating both the parents.
   Show answer

   (a) self pollinating ${\text{F}}_1$ generation plants

   Step-by-step solution →
8. Q88 CBSE 2025
   When a ​pure-tall pea ​plant is crossed with a ​pure-dwarf pea ​plant, the percentage of tall pea plants ​in $F_1$ and $F_2$ generation pea plants ​will be ​respectively :

   1. (a)$100\%$ ; $25\%$
   2. (b)$100\%$ ; $50\%$
   3. (c)$100\%$ ; $75\%$
   4. (d)$100\%$ ; $100\%$
   Show answer

   (c) $100\%$ ; $75\%$

   Step-by-step solution →
9. Q89 CBSE 2025
   The unit of heredity is :

   1. (a)Chromosome
   2. (b)Chromatin
   3. (c)Gene
   4. (d)DNA
   Show answer

   (c) Gene

   Step-by-step solution →
10. Q90 CBSE 2025
    In garden pea, violet ​colour flower ​is the dominant trait over ​white colour flower which is the recessive ​trait. When parent plant with violet ​coloured flowers (Vv) is crossed with a parent ​plant with white ​flowers, the possible percentage of occurrence of traits in the F1 progeny ​would be :

    1. (a)$100\%$ violet
    2. (b)$50\%$ violet, $50\%$ white
    3. (c)$25\%$ violet, $75\%$ white
    4. (d)$75\%$ violet, $25\%$ white
    Show answer

    (b) $50\%$ violet, $50\%$ white

    Step-by-step solution →
11. Q91 CBSE 2025
    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 :

    1. (a)$50\%$ round and green
    2. (b)$75\%$ wrinkled and green
    3. (c)$100\%$ round and yellow
    4. (d)$75\%$ wrinkled and yellow
    Show answer

    (c) $100\%$ round and yellow

    Step-by-step solution →
12. Q92 CBSE 2025
    A cross ​made between two pea plants ​produces ​50% ​tall ​and 50% short ​pea ​plants. The gene combination of the parental pea ​plants must be :

    1. (a)TT and tt
    2. (b)Tt and Tt
    3. (c)Tt and tt
    4. (d)TT and Tt
    Show answer

    (c) Tt and tt

    Step-by-step solution →
13. Q93 CBSE 2025
    Two statements are given — ​one ​labelled ​as Assertion (A) and the other labelled as ​Reason (R). Select the correct answer to this question from the ​codes ​(a), (b), (c) and ​(d) as ​given below.

    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.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer

    (c) Assertion (A) is true, but Reason (R) is false.

    Step-by-step solution →
14. Q94 CBSE 2025
    Two statements are given ​— ​one ​labelled as Assertion (A) and the other labelled as Reason (R). Select the ​correct answer ​from the codes ​given below.

    Assertion (A): A mango seed will germinate to form a mango tree.

    Reason (R): Heredity determines the process by which traits and characteristics are reliably inherited from parents to offspring.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer

    (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).

    Step-by-step solution →
15. Q95 CBSE 2025
    Two statements ​are given — one labelled Assertion ​(A) and ​the other labelled Reason (R). Select the correct answer ​to ​this question from the ​codes ​(a), (b), ​(c) and (d) given below.

    Assertion (A): In reptiles, the temperature at which the fertilized eggs are kept decides the sex of the offsprings.

    Reason (R): Sex is not genetically determined in some animals.

    1. (a)Both, Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
    2. (b)Both, Assertion (A) and Reason (R) are true, and Reason (R) is not the correct explanation of Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer

    (a) Both, Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).

    Step-by-step solution →
16. Q96 CBSE 2025
    “Proteins control ​the expression of various characters.” ​Explain ​this statement by taking ​an ​example of ​“tallness” as ​a characteristic in ​plants.
    Show answer

    Tallness depends on a hormone made by an enzyme (a protein) coded by a gene; an altered gene gives a short plant.

    A gene carries the information for making a protein, so a character can only be expressed through a protein. The height of a plant depends on the amount of plant growth hormone it makes, and that hormone is made by an enzyme, which is a protein. If the gene works efficiently, plenty of the active enzyme is made, plenty of hormone is produced and the plant is tall. If that gene is altered so that the enzyme is less efficient, less hormone is made and the plant remains short. Tallness is therefore controlled by the protein the gene codes for, which is what is meant by saying that proteins control the expression of characters.

    Step-by-step solution →
17. Q97 CBSE 2025
    Explain ​the mechanism of inheritance ​used ​by sexually reproducing organisms ​to ​ensure the stability ​of DNA ​of the ​species.
    Show answer

    Gametes carry half the chromosomes and fertilisation restores the full number, so the species' DNA stays stable from generation to generation.

    In sexually reproducing organisms the germ cells, or gametes, are made by a special cell division that halves the chromosome number, so a gamete carries only one set of chromosomes, $n$, while a body cell carries two, $2n$. At fertilisation a male gamete fuses with a female gamete, so the zygote receives one set from each parent and the full number $2n$ is restored. In a human, $23+23=46$. The halving and the doubling cancel exactly, so the amount of DNA and the number of chromosomes of the species stay stable from generation to generation, even though each offspring gets a fresh combination of genes.

    Step-by-step solution →
18. Q98 CBSE 2025
    1. (a)Explain how the proteins ​control the 'characteristics' ​in an organism with the help of ​an example of 'tallness' trait ​in ​pea ​plant.
    2. (b)Name the section ​of DNA that controls the 'characteristics' in an organism.
    Show answer

    (a) An efficient gene gives plenty of gibberellin and a tall plant, an altered gene gives a dwarf; (b) a gene.

    (a) A gene does not produce a characteristic directly: it carries the information for making a protein. In the pea plant the height depends on the amount of the hormone gibberellin, and gibberellin is made by an enzyme, which is a protein coded for by a gene. If the gene works efficiently, plenty of the enzyme and so plenty of gibberellin is made and the plant is tall; if the gene is altered, the enzyme is less efficient, less gibberellin is made and the plant is dwarf. So the gene controls the protein, and the protein controls the characteristic. (b) The section of DNA that controls a characteristic is called a gene.

    Step-by-step solution →
19. Q99 CBSE 2025
    Explain with ​the ​help of a flow chart that ​in ​human beings ​father is ​responsible ​for ​the sex (male or female) of the child.
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    Every egg carries X but sperms carry X or Y, so the father's sperm decides the child's sex.

    A human mother is $44+\text{XX}$ and a father is $44+\text{XY}$. In gamete formation each gamete receives one chromosome of each pair, so every egg carries $22+\text{X}$, while half the sperms carry $22+\text{X}$ and half carry $22+\text{Y}$. At fertilisation, an X-carrying sperm gives a zygote $44+\text{XX}$, which develops into a girl, and a Y-carrying sperm gives $44+\text{XY}$, which develops into a boy. Since the mother can contribute only an X, the sex of the child depends entirely on which kind of sperm fertilises the egg, so the father is responsible for the sex of the child.

    Step-by-step solution →
20. Q100 CBSE 2025
    1. (a)Explain how the proteins control the ‘characteristics’ in ​an organism with ​the ​help of an ​example ​of ‘short height’ trait in pea plant.
    2. (b)​Name ​the information source of ​making proteins in a cell.
    Show answer

    (a) An altered gene gives a less efficient enzyme, so less growth hormone is made and the pea plant stays short; (b) DNA.

    (a) Proteins control characteristics; many of them work as enzymes. Plant height depends on the amount of a growth hormone, which is made by a process that needs a particular enzyme. In a short pea plant the gene for this enzyme has an alteration that makes the enzyme less efficient, so less hormone is made and the plant stays short; with an efficient enzyme a lot of hormone is made and the plant grows tall. Thus genes control traits through the proteins made from them. (b) Cellular DNA is the information source for making proteins; the section of DNA that carries the information for one protein is its gene.

    Step-by-step solution →