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In a genetic experiment… (Class 10 Science SQP 2025-26, Q14)

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ScienceCBSE Class 10 · Sample paper, session 2025-26 · 3 marks · Short answer

CBSE Class 10 Science sample paper 2025-26: question 14

From the official CBSE sample question paper for 2025-26, section A, question 14, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q14 · 3 marks · Short answerHeredity

In a genetic experiment, plants with pure round green seeds () were crossed with plants with wrinkled yellow seeds ().

  1. (i)

    Show the gametes formed when F1 was self-pollinated.

    1 mark
  2. (ii)

    A total of 144 seeds were produced which developed into saplings. Show the ratio in which these traits are independently inherited in these 144 saplings.

    2 marks

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2025-26.

Hints

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

Hint 1

First find the F1 genotype from the parents' gametes.

Hint 2

A dihybrid F2 has 16 boxes. How many saplings does each box stand for out of 144?

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. Cross: RRyy (round green) × rrYY (wrinkled yellow). The parents' gametes are Ry and rY, so the F1 is RrYy (round yellow).

  2. (i) When F1 (RrYy) is self-pollinated, each plant forms four kinds of gametes in equal numbers: RY, Ry, rY, ry.

    1 mark

  3. (ii) A 4 × 4 checkerboard gives 16 combinations. Since the two traits are inherited independently, the phenotypes occur in the ratio Round yellow : Round green : Wrinkled yellow : Wrinkled green = 9 : 3 : 3 : 1.

    1 mark

  4. For 144 saplings, one part = . Round yellow = ; Round green = ; Wrinkled yellow = ; Wrinkled green = .

    1 mark

Answer: (i) Gametes: RY, Ry, rY, ry; (ii) 9:3:3:1, i.e. round yellow 81, round green 27, wrinkled yellow 27, wrinkled green 9

Where the marks are

  • Writes the four F1 gametes RY, Ry, rY, ry (1 mark)
  • Gives the 9:3:3:1 dihybrid ratio with correct phenotypes (1 mark)
  • Converts the ratio to 81 : 27 : 27 : 9 out of 144 (1 mark)

Revise the chapter

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 2025-26: 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.