Heredity — Class 10 Science PYQs

19 previous-year board questions (2026) with marking-scheme solutions, grouped by topic and marks.

Try each question first, then press ↓ (or tap Show Solution) to reveal the answer. Press ↓ again for the next question.

Marks:

Heredity: inherited traits; Mendel's experiments and laws

1 Mark Questions
11 Mark · March 2026 · Standardopen â†—
Choose the correct statements with reference to chromosomes :
(i) carry hereditary information from parents to next generation.
(ii) are thread-like structures located inside the nucleus of an animal cell.
(iii) always exist in pairs in human gametes.
(iv) are involved in the process of cell division.
  • (a)(i) and (ii)
  • (b)(iii) and (iv)
  • (c)(i), (ii) and (iv)
  • (d)(ii), (iii) and (iv)
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(C)/ (i), (ii) and (iv) (1 Mark)
21 Mark · March 2026 · Standardopen â†—
The number of chromosomes in parents and offspring of a particular species undergoing sexual reproduction remains constant due to :
  • (a)doubling of chromosomes after zygote formation.
  • (b)halving of chromosomes after zygote formation.
  • (c)doubling of chromosomes before gamete formation.
  • (d)halving of chromosomes at the time of gamete formation.
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(D) halving of chromosomes at the time of gamete formation.
31 Mark · March 2026 · Standardopen â†—
Identify the traits that cannot be transmitted from parents to the off springs :
(i) Swimming technique
(ii) Blood group
(iii) Eye colour
(iv) Dancing skills
Options :
  • (a)(i) and (ii)
  • (b)(i) and (iv)
  • (c)(iii) and (iv)
  • (d)(ii) and (iii)
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(B) / (i) and (iv)
41 Mark · March 2026 · Standardopen â†—
Question Nos. 8 & 9 consists of two statements : Assertion
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(A) / Both, Assertion (A) and Reason (R) are true, and Reason (R) is correct explanation of Assertion (A). (1 Mark)
2 Marks Questions
52 Marks · March 2026 · Standardopen â†—
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 :
(a) Why only tall pea plants were observed in $\text{F}_1$ progeny ?
(b) By which method did Mendel obtain $\text{F}_2$ progeny ?
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(a) In F1 progeny, pea plants have ‘Tt' where ‘T' is dominant over ‘t'
so all the plants of F1 progeny were tall. / Tall height is dominant
trait over short height. (1)
(b) Self-pollination (1)
(c) (i)
Dominant trait
i) Expresses itself over recessive trait.
ii) Expresses in both conditions-TT and Tt. (2)
Recessive trait
i) Unable to express itself in presence of a dominant trait.
ii) Expresses itself only when it is 'tt' or in pure condition. (2)
(any one, any other suitable difference)
OR
(c) (ii) Mendel's observations:
• All plants of F1 progeny were tall.
• No medium/ no short height plants observed in F1 progeny.
• F1 progeny resembled one parent only. (1+1)
(any two observations)
62 Marks · March 2026 · Standardopen â†—
(c) (i) Write one difference between dominant and recessive trait.
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(a) In F1 progeny, pea plants have ‘Tt' where ‘T' is dominant over ‘t'
so all the plants of F1 progeny were tall. / Tall height is dominant
trait over short height. (1)
(b) Self-pollination (1)
(c) (i)
Dominant trait
i) Expresses itself over recessive trait.
ii) Expresses in both conditions-TT and Tt. (2)
Recessive trait
i) Unable to express itself in presence of a dominant trait.
ii) Expresses itself only when it is 'tt' or in pure condition. (2)
(any one, any other suitable difference)
OR
(c) (ii) Mendel's observations:
• All plants of F1 progeny were tall.
• No medium/ no short height plants observed in F1 progeny.
• F1 progeny resembled one parent only. (1+1)
(any two observations)
72 Marks · March 2026 · Standardopen â†—
(c) (ii) Write two observations made by Mendel about $\text{F}_1$ progeny.
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(a) In F1 progeny, pea plants have ‘Tt' where ‘T' is dominant over ‘t'
so all the plants of F1 progeny were tall. / Tall height is dominant
trait over short height. (1)
(b) Self-pollination (1)
(c) (i)
Dominant trait
i) Expresses itself over recessive trait.
ii) Expresses in both conditions-TT and Tt. (2)
Recessive trait
i) Unable to express itself in presence of a dominant trait.
ii) Expresses itself only when it is 'tt' or in pure condition. (2)
(any one, any other suitable difference)
OR
(c) (ii) Mendel's observations:
• All plants of F1 progeny were tall.
• No medium/ no short height plants observed in F1 progeny.
• F1 progeny resembled one parent only. (1+1)
(any two observations)
82 Marks · March 2026 · Standardopen â†—
"Variation is useful for the survival of species over time." Explain this statement with the help of an example.
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Variation provides chance for species to survive under unfavourable / changing environmental conditions. e.g. if there were a population of bacteria living in temperate waters and if water temperature increased by global warming, most of these bacteria would die but the few variants resistant to heat would survive and grow further.
(or any other suitable example)
92 Marks · March 2026 · Standardopen â†—
Do all variations in a species have equal chances of surviving in the environment in which they find themselves ? Explain.
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* No (½ Mark)
* Different variations give different advantages to organisms and only those which are beneficial to the organisms for survival are passed on to their progeny. Example- if there were a population of bacteria living in temperate waters and if water temperature increased by global warming, most of these bacteria would die but the few variants resistant to heat would survive and grow further. (1½ Marks)
3 Marks Questions
103 Marks · March 2026 · Standardopen â†—
A blue colour flower (BB) bearing plant is crossed with a plant with white coloured flowers (bb).
(a) State the colour of the flowers you would expect in their $\text{F}_1$ progeny.
(b) What must be the percentage of white flower plants in the $\text{F}_2$ generation, if the $\text{F}_1$ plants are self-pollinated ?
(c) State the expected ratio of genotypes BB and bb in $\text{F}_2$ progeny.
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(a) All Blue flowers
(b) Parents: BB $\times$ bb
Gametes (B) (b)
F1 Bb (Blue)
Self Pollination Bb $\times$ Bb
Gametes (B), (b)
B BB Bb
b Bb bb
25% flowers are white
(Blue: White= 3:1, $\frac{1}{2} \times 100 = 25$)
(c) BB: bb :: 1: 1
4 Marks Questions
114 Marks · March 2026 · Standardopen â†—
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 :
(a) Why only tall pea plants were observed in $\text{F}_1$ progeny ?
(b) By which method did Mendel obtain $\text{F}_2$ progeny?
(c) (i) Write one difference between dominant and recessive trait.
OR
(c) (ii) Write two observations made by Mendel about $\text{F}_1$ progeny.
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(a) In F1 progeny, pea plants have ‘Tt' where ‘T’ is dominant over ‘t’
so all the plants of F1 progeny were tall. / Tall height is dominant
1
trait over short height.
(b) Self-pollination
1
(c) (i)
Dominant trait
Recessive trait
i) Expresses itself over
i) Unable to express itself
recessive trait.
in presence of a
2
dominant trait.
ii) Expresses in both
ii) Expresses itself only
conditions-TT and Tt.
when it is 'tt' or in pure
condition.
(any one, any other suitable difference)

Monohybrid and dihybrid inheritance

1 Mark Questions
121 Mark · March 2026 · Standardopen â†—
The genotype of green stemmed tomato plant is denoted by 'GG' and that of purple stemmed tomato plant as 'gg'. Hybrid of a cross between these two were self-pollinated to obtain $\text{F}_2$ progeny. What will be the ratio of GG, Gg and gg in this $\text{F}_2$ progeny ?
  • (a)2:1:1
  • (b)3:1:0
  • (c)1:1:2
  • (d)1:2:1
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(D) / 1:2:1 (1 Mark)
131 Mark · March 2026 · Standardopen â†—
Two pea plants, one with round green seeds (RRyy) and another with wrinkled yellow (rrYY) seeds were crossed with each other which produced $F_1$ progeny that have only round yellow (RrYy) seeds. When $F_1$ plants are self-pollinated, the $F_2$ progeny will have which new combination of characters, as compared to the parents :
(i) Round, yellow
(ii) Round, green
(iii) Wrinkled, yellow
(iv) Wrinkled, green
Correct options are :
  • (a)(i) and (ii)
  • (b)(i) and (iv)
  • (c)(ii) and (iv)
  • (d)(i) and (iii)
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(B) / (i) and (iv) (1 Mark)
141 Mark · March 2026 · Standardopen â†—
Round, green seeded pea plant (RRyy) was crossed with wrinkled, yellow seeded pea plant (rrYY), and $\text{F}_1$ progeny is produced.
All plants of $\text{F}_1$ progeny will have :
  • (a)round and green seeds
  • (b)round and yellow seeds
  • (c)wrinkled and green seeds
  • (d)wrinkled and yellow seeds
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(B)/ Round and yellow seeds (1 Mark)
3 Marks Questions
153 Marks · March 2026 · Standardopen â†—
Use the following information for Pea plants :
Dominant allele for tall plants – T
Recessive allele for short plants – t
Dominant allele for purple flowers – P
Recessive allele for white flowers – p
(a) Perform a cross between pure plant dominant for both the traits with another plant which is recessive for both the traits and work out the progeny upto $\text{F}_2$ generation.
(b) What is the probability of obtaining tall plants with white flowers in $\text{F}_2$ progeny?
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(a) Parents: TTPP (tall purple) x ttpp (short white)
Gametes: TP, tp
$F_1$: TtPp
Selfing of $F_1$: TtPp x TtPp (1 Mark)
$F_2$ gametes: TP, Tp, tP, tp.
Phenotypic ratio: tall and purple: 9, tall and white: 3, short and purple: 3, short and white: 1 (1 Mark)
(b) In $F_2$ progeny probability of Tall, White = 3/16 (1 Mark)

Sex determination

1 Mark Questions
161 Mark · March 2026 · Standardopen â†—
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 ?
(i) Gamete carrying X chromosome from female parent.
(ii) Gamete carrying X chromosome from male parent.
(iii) Gamete carrying Y chromosome from male parent.
Options:
  • (a)(ii) and (iii)
  • (b)(i) only
  • (c)(i) and (iii)
  • (d)(iii) only
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(A) / (ii) and (iii) (1)
171 Mark · March 2026 · Standardopen â†—
When a human egg is fertilized by a sperm having ‘Y’ chromosome, the zygote has the following combination of chromosomes :
  • (a)44 + XX
  • (b)22 + XX
  • (c)44 + XY
  • (d)22 + XY
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(C)/ 44 + XY (1 Mark)
3 Marks Questions
183 Marks · March 2026 · Standardopen â†—
(a) A couple are parents to 4 daughters in a sequence, and do not have any son. Does this indicate that the husband does not produced Y-chromosome bearing sperms ? Explain.
(b) What are the chances of this couple bearing yet another daughter ? Show with the help of a cross.
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Solution not available.
193 Marks · March 2026 · Standardopen â†—
(a) Giving two examples, justify the statement that the sex of the offspring in all animals is not always genetically determined.
(b) Differentiate between the sex chromosomes of male and female human beings.
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(a)
* In a few reptiles, the temperature at which fertilised eggs are kept determine whether the animal developing from the eggs will be male or female. (1 Mark)
* In snails, individuals can change sex. (1 Mark) (Any other example)
(b)
* Male sex chromosome: Male has a mismatched pair i.e, 'XY' chromosomes. (1 Mark)
* Female sex chromosome: Female has a perfect pair i.e. 'XX' chromosomes. (1 Mark)
* Male sex chromosome: Y chromosome is smaller than X chromosome. (1 Mark)
* Female sex chromosome: Both X chromosomes are of same size. (1 Mark) (Any one difference, Any other difference)