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Assertion (A): In humans, if… (Class 10 Science 2023, Q18)

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ScienceCBSE Class 10 · Board exam 2023, set 31/4/1 · 1 mark · Assertion-reason

CBSE Class 10 Science 2023: question 18

Set in the CBSE Class 10 board exam of 2023, paper 31/4/1, section A, question 18, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q18 · 1 mark · Assertion-reasonCompetency-basedHeredity

Assertion (A): In humans, if gene (B) is responsible for black eyes and gene (b) is responsible for brown eyes, then the colour of eyes of the progeny having gene combination Bb, bb or BB will be black only.

Reason (R): The black colour of the eyes is a dominant trait.

  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 2023 board paper, set 31/4/1.

Hints

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

Hint 1

Check each genotype one by one.

Hint 2

What does a homozygous recessive individual show?

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. B is dominant, so BB and Bb give black eyes, but bb gives brown eyes. Therefore A is false.

  2. R is true, because black is the dominant trait. Option (D) is correct.

    1 mark

Answer: Option (D)

Where the marks are

  • A false, R true (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 paper2023 board paper, set 31/4/1: 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.