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Study the cross given below… (Class 12 Biology 2025, Q19)

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BiologyCBSE Class 12 · Board exam 2025, set 57/1/1 · 2 marks · Very short answer

CBSE Class 12 Biology 2025: question 19

Set in the CBSE Class 12 board exam of 2025, paper 57/1/1, section B, question 19, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q19 · 2 marks · Very short answerCompetency-basedPrinciples of Inheritance and Variation

Study the cross given below :

Identify the abnormalities '1' and '2' in the offsprings of a cross done between a couple and distinguish between them.

Figure in the paper: Cross between parents 44+XY (male) and 44+XX (female). Male gametes: 22+XY and 22+O. Female gametes: 22+X and 22+X. Lines join gametes to offspring groups: group '1' (offsprings from fusion involving 22+XY gamete with 22+X, i.e. 44+XXY) and group '2' (from 22+O gamete with 22+X, i.e. 44+XO). See it in the official paper.

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

Add the gametes in each case to work out the chromosome complement of the offspring.

Hint 2

XXY and XO are two well-known sex-chromosome aneuploidies. Which has one chromosome extra and which has one missing?

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. 1 = Klinefelter's syndrome (44 + XXY). It results from fusion of the abnormal 22 + XY sperm with a normal 22 + X egg.

    ½ mark

  2. 2 = Turner's syndrome (44 + XO). It results from fusion of the 22 + O sperm with a 22 + X egg.

    ½ mark
  3. Klinefelter's syndromeTurner's syndrome
    Extra X chromosome; 47 chromosomes (trisomy of sex chromosomes)One X chromosome missing; 45 chromosomes (monosomy)
    Sterile male with overall masculine development but feminine features such as gynaecomastia; tall statureSterile female with rudimentary ovaries, short stature and lack of secondary sexual characters
    1 mark

Answer: 1 = Klinefelter's syndrome (44+XXY, sterile male); 2 = Turner's syndrome (44+XO, sterile female).

Where the marks are

  • Identifies 1 as Klinefelter's syndrome (½ mark)
  • Identifies 2 as Turner's syndrome (½ mark)
  • Any one correct difference, e.g. 47 chromosomes/extra X vs 45 chromosomes/missing X, or sterile male vs sterile female (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.