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Explain with the help of a… (Class 10 Science 2025, Q24)

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ScienceCBSE Class 10 · Board exam 2025, set 31/4/1 · 2 marks · Very short answer

CBSE Class 10 Science 2025: question 24

Set in the CBSE Class 10 board exam of 2025, paper 31/4/1, section B, question 24, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q24 · 2 marks · Very short answerHeredity

Explain with the help of a flow chart that in human beings father is responsible for the sex (male or female) of the child.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/4/1.

Hints

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

Hint 1

Write the sex chromosomes of the father and the mother.

Hint 2

Which parent can produce two different kinds of gametes?

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. Flow chart

    Father (XY) → sperms: 50% carry X, 50% carry Y

    Mother (XX) → all ova carry X

    Sperm (X) + Ovum (X) → zygote XX → girl

    Sperm (Y) + Ovum (X) → zygote XY → boy

    1 mark

  2. The mother can only give an X chromosome, but the father can give either X or Y. So the sex of the child depends on which type of sperm fertilises the ovum. Therefore the father is responsible for the sex of the child.

    1 mark

Answer: X-sperm + X-ovum gives XX (girl); Y-sperm + X-ovum gives XY (boy). Only the father can contribute Y, so the father decides the sex of the child.

Where the marks are

  • Flow chart showing XY father and XX mother with the X/Y sperm and X ovum combinations (1 mark)
  • Concludes that X-sperm gives a girl and Y-sperm gives a boy, so the father decides the sex (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 paper2025 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.