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Explain the mechanism of… (Class 10 Science 2025, Q23b)

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ScienceCBSE Class 10 · Board exam 2025, set 31/6/1 · 2 marks · Very short answer

CBSE Class 10 Science 2025: question 23(b)

Set in the CBSE Class 10 board exam of 2025, paper 31/6/1, section B, question 23(b), for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q23(b) · 2 marks · Very short answerHeredity

Explain the mechanism of inheritance used by sexually reproducing organisms to ensure the stability of DNA of the species.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/6/1.

Hints

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

Hint 1

If gametes carried the full chromosome number, what would happen to the zygote's chromosome number each generation?

Hint 2

Think about how many chromosomes of each pair go into a gamete, and what fertilisation does.

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. Every body cell has two copies of each chromosome, one from the male parent and one from the female parent. During gamete formation (meiosis), each germ cell receives only one chromosome from each pair, so a gamete has half the number of chromosomes (a single set).

    1 mark

  2. At fertilisation, a male gamete and a female gamete fuse. The zygote then gets the normal (paired) number of chromosomes again. In this way the chromosome number and DNA content stay constant from generation to generation, keeping the DNA of the species stable.

    1 mark

Answer: Gametes carry a single set of chromosomes (half the number); their fusion at fertilisation restores the full number, so DNA content stays constant.

Where the marks are

  • States that gametes get one chromosome of each pair, i.e. half the chromosome number (1 mark)
  • Explains that fusion of gametes restores the normal number, keeping DNA stable (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 paper2025 board paper, set 31/6/1: 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.