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Assertion (A) : When the two… (Class 12 Biology 2025, Q16)

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BiologyCBSE Class 12 · Board exam 2025, set 57/1/1 · 1 mark · Assertion-reason

CBSE Class 12 Biology 2025: question 16

Set in the CBSE Class 12 board exam of 2025, paper 57/1/1, section A, question 16, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q16 · 1 mark · Assertion-reasonCompetency-basedPrinciples of Inheritance and Variation

Assertion (A) : When the two genes in a dihybrid cross are situated on the same chromosome, the proportion of parental gene combinations is much higher than non-parental type.
Reason (R) : Higher parental gene combinations can be attributed to crossing over between two genes.

  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.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 57/1/1.

Hints

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

Hint 1

Ask what crossing over produces.

Hint 2

Recombinants come from crossing over.

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. Assertion (A) is true: tightly linked genes give far more parental combinations than recombinants.

  2. Reason (R) is false: crossing over produces the non-parental (recombinant) types. Parental types are high because linked genes tend to stay together. The answer is option (C).

    1 mark

Answer: Option (C)

Where the marks are

  • A true, R false (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Principles of Inheritance and Variation, one at a time, marked against the answer key and marking points.Back to the full paper2025 board paper, set 57/1/1: 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.