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In order to study… (Class 10 Science SQP 2026-27, Q15)

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ScienceCBSE Class 10 · Sample paper, session 2026-27 · 4 marks · Long answer

CBSE Class 10 Science sample paper 2026-27: question 15

From the official CBSE sample question paper for 2026-27, section A, question 15, for 4 marks. Try it first; the hints and our step-by-step solution are below.

Q15 · 4 marks · Long answerCompetency-basedHeredity

In order to study patterns of inheritance, Neha had performed typical Mendelian experiments with pea plants in the field. In experiment one, she crossed a pea plant having white flowers (vv) with another pea plant bearing violet flowers (VV). In another experiment, in addition to the colour of the flower she also focussed on the height of the pea plant. This time she crossed a pea plant having violet flowers and tall height (VVTT) with another pea plant having white flowers and short height (vvtt). What percentage is expected for the following traits as a result of these experiments? Give a reason.

  1. A

    Violet flowers in F1 and F2 generation in experiment one?

    1 mark
  2. B

    Tall height plants with white flowers in F2 generation in experiment two?

    1 mark
  3. C

    Attempt either sub-part C or D. Percentage of medium height plants with light violet flowers in F1 and F2 generations in experiment two? Give a reason.

    0 marks

  4. OR

    D

    Percentage of short height plants with white flowers in F1 and F2 generations in experiment two?

    2 marks

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2026-27.

Hints

Open one hint at a time and try again before the next.

Hint 1

Write the F1 genotype first, then self it.

Hint 2

For two traits, multiply the separate probabilities, e.g. P(vv) × P(T_).

Hint 3

Does Mendel's pea plant ever show a 'half-way' trait?

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. A. Cross: . All gametes are and , so all F1 plants are . Violet is dominant, so 100% violet in F1.

    ½ mark

  2. F1 selfed: . Violet plants , so 75% violet in F2, because a single dominant gives violet colour.

    ½ mark

  3. B. Cross: F1 all . Selfing F1 gives the dihybrid ratio 9 : 3 : 3 : 1. Tall white plants have genotype or : = 18.75%. This is a combination of one recessive and one dominant trait.

    1 mark

  4. C. (alternative to D, carries 2 marks if attempted instead): 0% in both F1 and F2. In pea plants these traits show complete dominance. A single or gives the same effect as two copies, so no blending or intermediate (medium height, light violet) plants are produced.

  5. D. F1: all plants are , showing only dominant traits (violet, tall). So short plants with white flowers = 0%.

    1 mark

  6. F2: short white plants must be double recessive : = 6.25%.

    1 mark

Answer: A. F1 100%, F2 75% violet; B. 3/16 = 18.75%; C. 0% in F1 and F2 (no intermediate traits, complete dominance); D. F1 0%, F2 1/16 = 6.25%.

Where the marks are

  • F1 100% and F2 75% violet with dominance reason (1 mark)
  • Tall white = 3/16 or 18.75% (1 mark)
  • C: 0% in both generations because no intermediate (blended) traits form (2 marks), OR
  • D: F1 0% since only dominant traits appear (1 mark); F2 1/16 or 6.25% as vvtt (1 mark)

Revise the chapter

  • Chapter: Heredity (notes, formulas, where marks are lost and every past question)
Practise this chapterBoard-style questions from Heredity, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2026-27: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.