Skip to content

A karyotype of a human… (Class 12 Biology 2025, Q21)

questionbuddy.in/q/cbse-12-biology-2025-57-7-1-q21-karyotype-human-suffering-certain-disorder

BiologyCBSE Class 12 · Board exam 2025, set 57/7/1 · 2 marks · Very short answer

CBSE Class 12 Biology 2025: question 21

Set in the CBSE Class 12 board exam of 2025, paper 57/7/1, section B, question 21, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q21 · 2 marks · Very short answerCompetency-basedPrinciples of Inheritance and Variation

A karyotype of a human suffering from a certain disorder is given below :
(a) Identify the disorder. (1/2)
(b) Write the symptoms of the disorder. (1/2)
(c) Give reason for such a disorder. (1)

Figure in the paper: Human karyotype with chromosome pairs numbered 1-22 and sex chromosomes labelled X X Y; the karyotype shows an extra X chromosome (XXY). See it in the official paper.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 57/7/1.

Hints

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

Hint 1

Count the sex chromosomes in the karyotype.

Hint 2

XXY points to a chromosomal disorder caused by a failure of segregation during meiosis.

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. (a) The karyotype shows 44 autosomes plus XXY (47 chromosomes), so the disorder is Klinefelter's syndrome.

    ½ mark

  2. (b) Symptoms: the person has an overall masculine build but shows feminine development, including development of breasts (gynaecomastia). He is sterile and often tall with feminised characters.

    ½ mark

  3. (c) Reason: the disorder is an aneuploidy. It is caused by non-disjunction, the failure of the sex chromosomes or chromatids to separate during gamete formation. A gamete with an extra X takes part in fertilisation, giving a male with XXY (trisomy of sex chromosomes).

    1 mark

Answer: (a) Klinefelter's syndrome; (b) gynaecomastia and sterility; (c) non-disjunction gives an extra X chromosome (47, XXY).

Where the marks are

  • Identifies Klinefelter's syndrome (½ mark)
  • Any correct symptom, such as gynaecomastia, sterility or feminised characters (½ mark)
  • Non-disjunction or aneuploidy giving an extra X in a male (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 57/7/1: 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.