Heredity Class 10 important questions with answers

What comes in the exam

• Heredity is in the World of Living unit, which is worth 25 marks in all.
• About a third of the questions are 1-mark MCQs.
• 3-mark questions, Assertion–Reason, 2-mark questions and 4-mark case studies come in similar numbers, and no 5-mark question has come from this chapter.
• Almost every year you get Mendel's crosses with one pair of traits (F1 and F2), crosses with two pairs (seed shape and colour), how genes control traits through proteins, and how sex is decided in humans.
• Questions on traits coming from both parents also come almost every year.

Top 10 Heredity questions from board papers

Real CBSE questions, printed as they appeared. Open each answer to see the marking and the steps.

1. Q1 MCQ · 1 mark CBSE · 2026

   F2 of round-green × wrinkled

   Two pea plants one with round green seeds (RRyy) and another with wrinkled yellow seeds (rrYY) were crossed. All the seeds of F1 progeny have round, yellow seeds (RrYy). When F1 plants are self-pollinated, the F2 progeny will have new combination of characters. (i) Round, yellow (ii) Round, green (iii) Wrinkled, yellow (iv) Wrinkled, green Choose the option that shows new combination of characters in F2 progeny.

   • (A) (i) and (ii)
   • (B) (i) and (iv)
   • (C) (iii) and (iv)
   • (D) (i) and (iii)
   Answer and marking

   Correct option: (B) (i) and (iv)

   1. Note the parents' combinations: round-green and wrinkled-yellow. Old combinations: round green, wrinkled yellow
   2. New ones are those not seen in either parent. Round yellow (i) and wrinkled green (iv) ⇒ Option (B) 1 mark

   Answer: (B) (i) and (iv)

   Marks: Correct option 1

   For full marks: 'New' means compared with the parents, not with F1.

   Where students lose marks: Picking (C) (iii) and (iv): wrinkled yellow was a parent, so it is not new.

   CBSE marking scheme

   Parents were round-green and wrinkled-yellow, so the new combinations in F2 are round-yellow (i) and wrinkled-green (iv).

   Write your answer, send a photo, get it marked in Dhee →
2. Q2 MCQ · 1 mark CBSE · 2026

   Zygote from a Y-bearing sperm

   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
   Answer and marking

   Correct option: (C) 44 + XY

   1. Add the egg's and the Y-sperm's chromosomes. Egg 22 + X ; Y-sperm 22 + Y
   2. Together they give the zygote. 44 + XY (a boy) ⇒ Option (C) 1 mark

   Answer: (C) 44 + XY

   Marks: Correct option 1

   For full marks: Write the full count: 44 autosomes plus the sex chromosomes.

   Where students lose marks: Picking (D) 22 + XY: forgetting both gametes add 22 autosomes each.

   CBSE marking scheme

   Egg gives 22 + X, sperm gives 22 + Y, so zygote = 44 + XY (a boy).

   Write your answer, send a photo, get it marked in Dhee →
3. Q3 Very short answer · 2 marks CBSE · 2025

   Proteins and tallness in plants

   "Proteins control the expression of various characters." Explain this statement by taking an example of "tallness" as a characteristic in plants.

   Answer and marking

   1. Trace height back from the hormone to the enzyme and the gene. Plant height depends on the amount of a plant hormone ; the amount made depends on the efficiency of an enzyme (a protein), which is coded by a gene 1 mark
   2. Now say how a good or poor enzyme changes the height. Efficient enzyme → more hormone → tall plant ; inefficient enzyme → less hormone → short plant 1 mark

   Answer: Gene → enzyme (protein) → amount of hormone → tall or short plant

   Marks: Gene to enzyme 1 · Enzyme to height 1

   For full marks: Write the word 'enzyme (a protein)'; the link between protein and the hormone amount is what the question tests.

   Where students lose marks: Saying the gene makes the plant tall directly, skipping the enzyme and the hormone in between.

   CBSE marking scheme

   Plant height depends on the amount of a particular plant hormone; the amount made depends on the efficiency of an enzyme (a protein) for that process, which is coded by a gene (DNA sequence). An efficient enzyme makes a lot of hormone and the plant is tall; an inefficient one makes the plant short (2).

   Write your answer, send a photo, get it marked in Dhee →
4. Q4 Very short answer · 2 marks CBSE · 2024

   Flow diagram: boy or girl chance

   In human beings, the probability of getting a male or a female child is 50%. Explain with the help of a flow diagram only.

   Answer and marking

   1. Start the flow diagram with the parents and the gametes each one makes. Father XY → sperms X or Y (half each) ; Mother XX → eggs only X 1 mark
   2. Join each sperm with the egg and read off the child. X sperm + X egg → XX (girl) ; Y sperm + X egg → XY (boy) ; so the chance of each is 50% 1 mark

   Answer: Father XY gives X or Y sperm, mother gives only X; XX girl, XY boy, so 50% each

   Marks: Parents and gametes 1 · Offspring 1

   For full marks: Show both gametes from the father, X and Y, in the diagram; the 50% comes from them being equal in number.

   Where students lose marks: Writing the mother as XY or giving her Y eggs; the mother is XX and every egg carries X.

   CBSE marking scheme

   Flow diagram: father XY gives sperms X or Y; mother XX gives only X eggs (½+½). X sperm + X egg → XX girl; Y sperm + X egg → XY boy (½+½), so each is 50%.

   Write your answer, send a photo, get it marked in Dhee →
5. Q5 Very short answer · 2 marks CBSE · 2023

   Mendel's TT × tt cross questions

   Mendel crossed a pure tall pea plant (TT) with a pure short pea plant (tt) and obtained all tall plants in F1 generation. (a) What is the gene combination present in the plants of F1 generation? (b) Give reason why only tall plants are observed in F1 progeny. (c) What will be the ratio of the plants obtained in the F2 generation when F1 plants are self-pollinated?

   Answer and marking

   1. (a) Write the gene pair each F1 plant gets, one from each parent. Tt 0.5 marks
   2. (b) Say which trait shows when both are present. Tallness is dominant ; only the dominant trait is expressed in F1. 1 mark
   3. (c) Give the F2 ratio after selfing F1. Tall : short = 3 : 1 0.5 marks

   Answer: (a) Tt ; (b) tallness is dominant ; (c) 3 tall : 1 short

   Marks: F1 genes ½ · Reason 1 · F2 ratio ½

   For full marks: In (b) use the word 'dominant'; the full mark rests on saying tallness is the dominant trait.

   Where students lose marks: Writing the genotype ratio 1 : 2 : 1 in (c) when the question asks for the plants, tall : short = 3 : 1.

   CBSE marking scheme

   (a) Tt (½). (b) Tallness is dominant; only the dominant trait is expressed in F1 (1). (c) Tall : short = 3 : 1 (½).

   Write your answer, send a photo, get it marked in Dhee →

6. Q6 Short answer · 3 marks CBSE · 2025

   Round yellow × wrinkled green

   A pure pea plant having round (R), yellow (Y) seeds is crossed with another pure pea plant having wrinkled (r), green (y) seeds. Subsequently F1 progeny is self-pollinated to obtain F2 progeny. (a) What do the seeds of F1 generation look like? (b) Give the possible combinations of traits in seeds of F2 generation. Also give their ratio. (c) State the reason of obtaining seeds of new combination of traits in F2 generation.

   Answer and marking

   1. (a) Show the dominant traits, since F1 gets one of each gene. Round, yellow seeds 1 mark
   2. (b) List all four F2 seed types with their numbers. Round yellow 9 : round green 3 : wrinkled yellow 3 : wrinkled green 1 1 mark
   3. (c) Explain why shape and colour can mix in new ways. The traits for shape and colour are inherited independently (independent inheritance of traits). 1 mark

   Answer: (a) Round yellow ; (b) 9 RY : 3 RG : 3 WY : 1 WG ; (c) traits are inherited independently

   Marks: F1 seeds 1 · F2 combinations and ratio 1 · Reason 1

   For full marks: In (c) write 'traits are inherited independently'; that is the line that explains round green and wrinkled yellow.

   Where students lose marks: Writing the 3 : 1 ratio in (b); two traits are followed here, so F2 gives 9 : 3 : 3 : 1.

   CBSE marking scheme

   (a) Round, yellow (1). (b) Round yellow 9 : round green 3 : wrinkled yellow 3 : wrinkled green 1 (1). (c) Traits are inherited independently / independent assortment (1).

   Write your answer, send a photo, get it marked in Dhee →
7. Q7 Case study · 4 marks CBSE · 2026

   Case: bread-wheat genome

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

   Answer and marking

   1. (a) Expand the short form. Deoxyribonucleic acid 1 mark
   2. (b) Name the division that halves the chromosome number. Meiosis (reduction division) ; the chromosome number is halved 1 mark
   3. (c)(i) Link India's climates to different wheat varieties. India has varied climates, so variant wheat varieties are needed 1 mark
   4. Say how a suited variety helps the crop survive. Farmers grow the variety best suited to their climate, giving better survival and better grain quality 1 mark
   5. (c)(ii) Say what a gene is. A section of DNA that codes for one protein is a gene. 1 mark
   6. Use plant height to show the chain from gene to trait. Height depends on a growth hormone, whose amount depends on an enzyme made from a gene ; a less efficient gene variant → less enzyme → less hormone → short plant 1 mark

   Answer: (a) Deoxyribonucleic acid ; (b) meiosis ; (c)(i) suited varieties survive varied climates / (c)(ii) gene → protein (enzyme) → hormone → trait

   Marks: (a) 1 · (b) 1 · (c) 2

   For full marks: In (c)(ii) start with 'a section of DNA that codes for a protein is a gene', then give the height example.

   Where students lose marks: Writing mitosis in (b); gametes form by meiosis, which halves the chromosome number.

   CBSE marking scheme

   (a) Deoxyribonucleic acid (1). (b) Meiosis - reduction division, chromosome number halved (1). (c)(i) India has varied climates; variant wheat varieties let farmers grow the variety best suited to a climate, giving better survival and grain quality (2). OR (c)(ii) A section of DNA that codes for one protein is a gene. E.g. plant height depends on a growth hormone whose amount depends on the efficiency of an enzyme made from a gene; a less efficient gene variant gives less enzyme, less hormone and a short plant (2).

   Write your answer, send a photo, get it marked in Dhee →
8. Q8 Case study · 4 marks CBSE · 2026

   Case: Mendel's tall × short

   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 F1 generation. Answer the following questions: (i) Why only tall pea plants were observed in F1 progeny? (1) (ii) By which method did Mendel obtain F2 progeny? (1) (iii) (a) Write one difference between dominant and recessive trait. (2) OR (iii) (b) Write two observations made by Mendel about F1 progeny. (2)

   Answer and marking

   1. (i) Give the F1 genes and say which one wins. F1 plants are Tt ; T (tall) is dominant over t, so all are tall 1 mark
   2. (ii) Name how F1 plants were bred to get F2. Self-pollination 1 mark
   3. (iii)(a) Say how a dominant trait shows itself. A dominant trait expresses itself over the recessive one, in both TT and Tt. 1 mark
   4. Now say when a recessive trait can show. A recessive trait cannot express itself when the dominant is present ; it shows only as tt. 1 mark
   5. (iii)(b) Give the first observation about F1 height. All F1 plants were tall. 1 mark
   6. Give a second observation. There were no medium or short plants in F1 (F1 resembled only one parent). 1 mark

   Answer: (i) Tt, tall is dominant ; (ii) self-pollination ; (iii)(a) dominant shows in TT and Tt, recessive only in tt / (iii)(b) all tall, no medium or short plants

   Marks: (i) 1 · (ii) 1 · (iii) 2

   For full marks: In (iii)(a) write the gene pairs, TT and Tt for dominant and tt for recessive; they make the difference exact.

   Where students lose marks: In (ii) writing cross-pollination; F2 came from self-pollinating the F1 plants.

   CBSE marking scheme

   (i) F1 plants are Tt and T (tall) is dominant over t, so all are tall (1). (ii) Self-pollination (1). (iii)(a) Dominant trait expresses itself over the recessive, in both TT and Tt; recessive trait cannot express itself in presence of the dominant, shows only as tt (2). OR (iii)(b) All F1 plants were tall; no medium/short plants in F1; F1 resembled only one parent (any two, 1+1).

   Write your answer, send a photo, get it marked in Dhee →
9. Q9 Case study · 4 marks CBSE · 2025

   Case: autosomes, sex chromosomes

   In human beings, there are 23 pairs of chromosomes. Out of these 23 pairs of chromosomes (i.e. 46 chromosomes), 22 pairs of chromosomes are called autosomes and one pair of chromosomes, i.e. two chromosomes, are called sex chromosomes. The sex chromosomes are of two types — 'X' chromosomes and 'Y' chromosomes. The sex of a child (i.e. progeny) is decided at the time of fertilisation. In other words, at the time of zygote formation the sex chromosomes inherited from the parents of a child decide whether the new born will be a boy or a girl. (i) What are chromosomes ? (ii) Why is the pair of sex chromosomes in human males called mismatched pair ? (iii) (A) Show with the help of a flow chart that the statistical probability of getting a boy or a girl is 50 : 50. OR (iii) (B) Mention two examples of animals where sex is not determined genetically like human beings. Describe in brief the method of sex determination in these animals.

   Answer and marking

   1. (i) Describe what chromosomes look like and what they carry. Thread-like structures carrying genes (DNA) that pass inherited information from parents to the next generation. 1 mark
   2. (ii) Compare the sizes of the two sex chromosomes in males. Males have one normal-sized X and one short Y chromosome. 1 mark
   3. (iii)(A) Start the flow chart with each parent's gametes. Mother XX → eggs only X ; Father XY → sperm X or Y in equal numbers 1 mark
   4. Join the gametes and read off the chances. X egg + X sperm → XX girl ; X egg + Y sperm → XY boy ; so 50 : 50 1 mark
   5. (iii)(B) Give the first animal and its cue. Some reptiles: the incubation temperature of the fertilised eggs decides the sex. 1 mark
   6. Give the second animal and what it can do. Snails can change sex, so their sex is not genetically determined. 1 mark

   Answer: (i) thread-like carriers of genes ; (ii) X normal, Y short ; (iii)(A) XX girl, XY boy, 50 : 50 / (iii)(B) reptiles: temperature, snails: change sex

   Marks: (i) 1 · (ii) 1 · (iii) 2

   For full marks: In (iii)(A) write 'X or Y sperm in equal numbers'; that is where the 50 : 50 comes from.

   Where students lose marks: In (iii)(B) naming reptiles and snails but not describing how sex is decided in each.

   CBSE marking scheme

   (i) Thread-like structures carrying genes / DNA that pass inherited information from parents to the next generation (1). (ii) Males have one normal-sized X and a short Y chromosome (1). (iii)(A) Flow chart: mother XX gives only X eggs; father XY gives X or Y sperm in equal numbers; X egg + X sperm → XX girl, X egg + Y sperm → XY boy, so 50 : 50 (2). OR (B) Some reptiles: incubation temperature of fertilised eggs decides sex (1); snails can change sex, so sex is not genetically determined (1).

   Write your answer, send a photo, get it marked in Dhee →
10. Q10 Case study · 4 marks CBSE · 2025

    Case: who determines baby's sex

    The process of determining the sex of a newborn is purely genetic. But still many people in some societies believe that only the woman (mother) is responsible for determination of the sex of the child and blame her. In fact, the sex of the child is genetically determined. But there are some animals where sex is not genetically determined. (i) Define sex chromosomes. (1) (ii) Mention one example of animals where sex is not genetically determined. How is sex determined in these animals? Explain. (1) (iii) Does the genetic combination of the mother play a significant role in determining the sex of newborn? Explain. (2) OR (iii) How is equal genetic contribution of male and female parents ensured in progeny? (2)

    Answer and marking

    1. (i) Say what these special chromosomes decide. Sex chromosomes are the pair of chromosomes that determine the sex of a person. 1 mark
    2. (ii) Name one animal and say what decides its sex. Some reptiles: the temperature at which the eggs are incubated decides the sex (or snails can change sex). 1 mark
    3. (iii) Answer the question first. No. 1 mark
    4. Then show why only the father's chromosome matters. The mother always gives an X ; X from the father → girl (XX), Y from the father → boy (XY) 1 mark
    5. (iii) Say how both parents make their gametes. Both parents form gametes by meiosis, which halves the chromosome number. 1 mark
    6. Then say what fertilisation brings together. Fusion at fertilisation restores the full set, half from each parent. 1 mark

    Answer: (i) the pair that decides sex ; (ii) reptiles: incubation temperature ; (iii) No, mother always gives X / (iii) gametes halve, fusion restores, half from each parent

    Marks: (i) 1 · (ii) 1 · (iii) 2

    For full marks: In (iii) write 'No' clearly first; that answer carries a full mark before the explanation.

    Where students lose marks: In (ii) naming the animal but not saying what decides its sex, such as temperature.

    CBSE marking scheme

    (i) The chromosome pair that determines sex in humans (1) (ii) Some reptiles/lizards – temperature of incubation; or snails – can change sex (environmental factors) (½+½) (iii) No (1); mother always gives X; a child getting X from father is a girl (XX), Y from father is a boy (XY) (1) OR (iii) Both parents form gametes by meiosis, halving chromosome number; fusion at fertilisation restores the full set, half from each parent (2)

    Write your answer, send a photo, get it marked in Dhee →

Free 10-question test: Heredity

MCQ and Assertion–Reason questions from CBSE papers. About 10 minutes. Your score shows straight away.

Common mistakes in Heredity

How to write for full marks

• Show every cross as a cross diagram or Punnett square: parents, gametes, F1, then F1 self-pollinated, then F2. Write the gene letters and how each plant looks. A cross diagram or a Punnett square both earn the marks.
• Use the letters the question gives, with a capital letter for the dominant trait, like T for tall and t for short.
• For 'dominant vs recessive', write both halves: a dominant trait shows with one copy; a recessive trait shows only when both copies are recessive. Each half carries ½ mark.
• In Assertion–Reason, judge A and R on their own first. Then ask whether R gives the reason for A. A true R can still fail to explain A.
• For 'give two examples where sex is not decided by genes', name two different animals and say how sex is decided in each. Each carries 1 mark.

Not in the 2026-27 exam

Leave these out of your revision.

• Evolution: school assessment only
• Sex determination beyond a brief introduction
• Information in the NCERT boxes

Questions students ask