Class 10 Science · Chapter 8

Heredity

285 Class 10 Science questions on Heredity from the NCERT textbook, NCERT Exemplar and CBSE board papers 2017–2026, each with its answer and a step-by-step solution.

CBSE Class 10 Science previous year papers, with answers →

Questions · page 8 of 15

1. Q141 CBSE 2024
   A plant having blue ​coloured flowers (BB) is crossed with a plant having white coloured flowers (bb) :

   1. (a)Name ​the term ​used for the trait, which is observed in ${\text{F}}_1$ generation. Give its ​gene combination.
   2. (b)If the plants obtained in ${\text{F}}_1$ generation are self-pollinated, write the percentage of (i) plants with flowers of blue colour, and (ii) plants with flowers of white colour in ${\text{F}}_2$ generation. What did the reappearance of plants ​with ​white coloured ​flowers in ${\text{F}}_2$ generation indicate ?
   Show answer

   The ${\text{F}}_1$ trait is dominant ($\text{Bb}$); ${\text{F}}_2$ is 75% blue and 25% white, white being a recessive trait hidden in ${\text{F}}_1$.

   (a) The trait seen in ${\text{F}}_1$ (blue) is the dominant trait; its gene combination is Bb. (b) In ${\text{F}}_2$, (i) $75\%$ of the plants have blue flowers and (ii) $25\%$ have white flowers (BB : Bb : bb $=1:2:1$, so blue : white $=3:1$). The reappearance of white flowers shows that the factor for white colour (b) was present in the ${\text{F}}_1$ plants but was not expressed because it is recessive; the two factors do not blend but remain separate and separate out when gametes form, so two b factors can come together again in ${\text{F}}_2$.

   Step-by-step solution →
2. Q142 CBSE 2024
   What is the probability ​of a male ​child or a ​female child being ​born ​in case of human ​beings ? Explain.
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   The probability of a male child and of a female child is $\frac{1}{2}$ (50%) each, because the father's sperm decides the sex.

   The probability is $\frac{1}{2}$ (50%) for a male child and $\frac{1}{2}$ (50%) for a female child. The mother (XX) produces only X-carrying eggs, while the father (XY) produces X-carrying and Y-carrying sperms in equal numbers. If an X-carrying sperm fertilises the egg the child is XX, a girl; if a Y-carrying sperm does, the child is XY, a boy. Both are equally likely, so the sex of the child is decided by the father's sperm, and each sex has an equal chance.

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3. Q143 CBSE 2024
   Is it ​possible ​that ​a ​trait gets inherited, ​but not expressed ? ​Give an example to ​justify your answer.
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   Yes: in Mendel's cross all ${\text{F}}_1$ plants were tall though they inherited the factor for shortness, which reappeared in one quarter of ${\text{F}}_2$.

   Yes. Example: Mendel crossed pure tall pea plants (TT) with pure short, or dwarf, pea plants (tt). All the ${\text{F}}_1$ plants were tall (Tt). Each ${\text{F}}_1$ plant had inherited the factor for shortness (t) from its short parent, but this trait was not expressed because the factor for tallness (T) is dominant. When the ${\text{F}}_1$ plants were self-pollinated, about one quarter of the ${\text{F}}_2$ plants were short (tt), in the ratio 3 tall : 1 short. The reappearance of short plants in ${\text{F}}_2$ shows that the shortness trait had been inherited by the ${\text{F}}_1$ plants but not expressed.

   Step-by-step solution →
4. Q144 CBSE 2024
   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.

   1. (i)When Mendel crossed pea plants with pure tall and pure short characteristics to produce ${\text{F}}_1$ progeny, which two observations were made by him in ${\text{F}}_1$ plants?[1]
   2. (ii)Write one difference between dominant and recessive trait.[1]
   3. (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.[2]
   4. (iii)(b)OR : Justify the statement : “It is possible that a trait is inherited but may not be expressed.”[2]
   Show answer

   ${\text{F}}_1$ plants are all tall; selfing them gives $9:3:3:1$ in ${\text{F}}_2$ and shows independent inheritance; a recessive trait can stay hidden.

   (i) (1) All the ${\text{F}}_1$ plants were tall. (2) No plant was short or of a medium height: only one parental trait (tallness) was expressed, not a mixture of the two. (ii) A dominant trait is expressed even when only one copy of its factor is present (as tallness in $\text{Tt}$ plants), whereas a recessive trait is expressed only when both copies are recessive (as shortness in $\text{tt}$ plants). (iii)(a) The ${\text{F}}_2$ generation was obtained by self-pollination of the ${\text{F}}_1$ plants (all $\text{RrYy}$, round yellow). The ${\text{F}}_2$ ratio is round yellow : round green : wrinkled yellow : wrinkled green $=9:3:3:1$, so the parental combinations, round yellow and wrinkled green, appear in the ratio $9:1$. Conclusions: round and yellow are dominant, and since new combinations (round green, wrinkled yellow) appear, the traits of seed shape and seed colour are inherited independently. (iii)(b) In a cross of pure tall ($\text{TT}$) and pure short ($\text{tt}$) plants, all the ${\text{F}}_1$ plants are tall ($\text{Tt}$): they carry the factor for shortness but do not express it, because tallness is dominant. On self-pollination of the ${\text{F}}_1$ plants, short ($\text{tt}$) plants reappear in ${\text{F}}_2$ (about one in four), so the short trait was inherited by the ${\text{F}}_1$ plants without being expressed.

   Step-by-step solution →
5. Q145 CBSE 2024
   In one of his ​famous experiments of tracing the inheritance of ​traits when Mendel cross-pollinated a pure tall pea plant with a pure ​dwarf pea plant, he got only tall ​pea plants in the ${\text{F}}_1$ generation. When ${\text{F}}_1$ tall pea plants ​were self-pollinated, Mendel got ${\text{F}}_2$ generation pea plants in which both tall and dwarf pea ​plants were present.

   1. (a)List any two pairs of contrasting characters, other than those mentioned above used by Mendel in his experiments.[1]
   2. (b)Differentiate between dominant and recessive traits.[1]
   3. (c)(i)State the ratio of tall pea plants and dwarf pea plants in ${\text{F}}_2$ generation. Give reason for the appearance of dwarf pea plants in ${\text{F}}_2$ generation.[2]
   4. (c)(ii)OR : Differentiate between ${\text{F}}_1$ generation and ${\text{F}}_2$ generation in context of Mendel’s experiment.[2]
   Show answer

   Round/wrinkled seeds and violet/white flowers; dominant shows with one copy; $F_2$ is 3 tall : 1 dwarf because $F_1$ plants are $\text{Tt}$.

   (a) Any two of: round and wrinkled seeds; violet and white flowers; yellow and green seeds. (b) A dominant trait is expressed even when only one copy of its gene is present (TT or Tt), so it is the trait seen in the ${\text{F}}_1$ (tallness); a recessive trait is expressed only when both copies are recessive (tt), so it stays hidden in the ${\text{F}}_1$ (dwarfness). (c)(i) Tall : dwarf = 3 : 1. The ${\text{F}}_1$ plants are Tt: they carry the recessive gene for dwarfness without expressing it. On self-pollination half the gametes of each plant carry t, and when two such gametes fuse the offspring is tt, which is dwarf (one plant in four). OR (c)(ii) ${\text{F}}_1$ generation: produced by cross-pollinating the pure tall (TT) and pure dwarf (tt) parents; all plants are tall and all are Tt (hybrid); only the dominant trait appears. ${\text{F}}_2$ generation: produced by self-pollinating the ${\text{F}}_1$ plants; tall and dwarf plants appear in the ratio 3 : 1 (TT : Tt : tt = 1 : 2 : 1); the recessive trait appears again.

   Step-by-step solution →
6. Q146 CBSE 2023
   In an ​experiment with pea plants, a pure tall plant (TT) is crossed ​with ​a ​pure short plant (tt). The ratio of pure tall plant to pure short ​plants in ${\text{F}}_2$ generation ​will ​be

   1. (a)$1:3$
   2. (b)$3:1$
   3. (c)$1:1$
   4. (d)$2:1$
   Show answer

   (c) $1:1$

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7. Q147 CBSE 2023
   The statement that ​correctly ​describes ​the ​characteristic(s) of ​a ​gene ​is :

   1. (a)In individuals of a given species, a specific gene is located on a particular chromosome.
   2. (b)A gene is not the information source for making proteins in the cell.
   3. (c)Each chromosome has only one gene located all along its length.
   4. (d)All the inherited traits in human beings are not controlled by genes.
   Show answer

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

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8. Q148 CBSE 2023
   A cross between ​pea plant with white flowers (vv) ​and pea plant ​with violet flowers (VV) ​resulted in $F_2$ progeny in which ratio ​of violet ​(VV) and white (vv) flowers will be ​:

   1. (a)$1:1$
   2. (b)$2:1$
   3. (c)$3:1$
   4. (d)$1:3$
   Show answer

   (a) $1:1$

   Step-by-step solution →
9. Q149 CBSE 2023
   Consider the following two ​statements :

   1. (i)The trait that expresses itself in $F_1$ generation.
   2. (ii)The trait that ​keeps on passing from one ​generation to another. The ​appropriate ​terms ​for the statements (i) and (ii) respectively ​are :

   1. (a)Recessive trait, Dominant trait
   2. (b)Dominant trait, Recessive trait
   3. (c)Dominant trait, Inherited trait
   4. (d)Recessive trait, Inherited trait
   Show answer

   (c) Dominant trait, Inherited trait

   Step-by-step solution →
10. Q150 CBSE 2023
    When a ​pure ​tall pea plant is crossed with a pure ​dwarf pea plant, the percentage ​of tall pea plant in ${\text{F}}_1$ and ${\text{F}}_2$ generation pea ​plants ​respectively will ​be :

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

    (c) 100%; 75%

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11. Q151 CBSE 2023
    Which pair ​of ​sex chromosome ​will determine ​a male ?

    1. (a)XO
    2. (b)XX
    3. (c)XY
    4. (d)YY
    Show answer

    (c) XY

    Step-by-step solution →
12. Q152 CBSE 2023
    Which one ​of ​the ​given ​statements ​is incorrect ​:

    1. (a)DNA has the complete information for a particular characteristic.
    2. (b)DNA is the molecule responsible for the inheritance of characters from parents to offsprings.
    3. (c)Change in information will produce a different protein.
    4. (d)Characteristics will remain the same even if protein changes.
    Show answer

    (d) Characteristics will remain the same even if protein changes.

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13. Q153 CBSE 2023
    In ​a cross between ​pure tall pea plants (TT) and pure ​dwarf pea plants (tt) the offsprings of $F_1$ ​generation ​were all tall. When $F_1$ generation was self-crossed, ​the gene combinations ​of the ​offsprings of $F_2$ generation will be :

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

    (a) TT : Tt : tt

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14. Q154 CBSE 2023
    When an ​'X' bearing ​sperm fertilises ​the ​egg, the ​resulting zygote ​has the following combination of ​chromosomes :

    1. (a)$44+\text{XX}$
    2. (b)$44+\text{XY}$
    3. (c)$22+\text{XX}$
    4. (d)$22+\text{XY}$
    Show answer

    (a) $44+\text{XX}$

    Step-by-step solution →
15. Q155 CBSE 2023
    These consist of ​two ​statements – Assertion (A) ​and Reason (R). Answer this question selecting the ​appropriate ​option ​given below :

    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.

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

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

    Step-by-step solution →
16. Q156 CBSE 2023
    These consist of ​two statements ​– Assertion (A) and Reason (R). Answer this ​question ​selecting ​the ​appropriate ​option ​given below.

    Assertion (A): In humans, if gene (B) is responsible for black eyes and gene (b) is responsible for brown eyes, then the colour of eyes of the progeny having gene combination Bb, bb or BB will be black only.

    Reason (R): The black colour of the eyes is a dominant trait.

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

    (d) (A) is false but (R) is true.

    Step-by-step solution →
17. Q157 CBSE 2023
    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): Human populations show a great deal of variations in traits.

    Reason (R): All variations in a species have equal chances of surviving in the environment in which they live.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the 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 →
18. Q158 CBSE 2023
    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): Human beings have one pair of sex chromosomes.

    Reason (R): All children, whether boys or girls, inherit an X-chromosome from their father.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the 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 →
19. Q159 CBSE 2023
    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): Each human trait is influenced by both paternal and maternal DNA.

    Reason (R): As compared to the father, the mother contributes more amount of genetic material to the child.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the 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 →
20. Q160 CBSE 2023
    Mendel crossed a pure tall ​pea plant ​(TT) with a pure short pea ​plant ​(tt) and obtained all tall plants in ${\text{F}}_1$ generation.

    1. (a)What is the ​gene combination present in the plants ​of ${\text{F}}_1$ generation ?
    2. (b)Give ​reason why only tall plants are observed in ${\text{F}}_1$ progeny.
    3. (c)What will be the ratio of the plants obtained in ​the ${\text{F}}_2$ generation when ${\text{F}}_1$ plants are self-pollinated ?
    Show answer

    (a) The gene combination is Tt; (b) tallness (T) is dominant over shortness (t); (c) tall : short = 3 : 1 in ${\text{F}}_2$.

    (a) Every plant of the ${\text{F}}_1$ generation has the gene combination $Tt$, one allele from each parent. (b) $T$, the allele for tallness, is dominant over $t$, the allele for shortness, so a single $T$ is enough to make the plant tall and the effect of $t$ remains hidden. Every ${\text{F}}_1$ plant is $Tt$, so every one of them is tall. (c) On self-pollinating the ${\text{F}}_1$ plants the ${\text{F}}_2$ generation shows tall : short $=3:1$ (the underlying genotypic ratio being $1TT:2Tt:1tt$).

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