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Analyse the following two… (Class 12 Biology 2026, Q20a)

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BiologyCBSE Class 12 · Board exam 2026, set 57/1/1 · 2 marks · Very short answer

CBSE Class 12 Biology 2026: question 20(a)

Set in the CBSE Class 12 board exam of 2026, paper 57/1/1, section B, question 20(a), for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q20(a) · 2 marks · Very short answerCompetency-basedPrinciples of Inheritance and Variation

Analyse the following two cases of sex determination in different organisms :
Case I : Males have (XO) sex chromosomes and females have two copies of same sex chromosome (XX).
Case II : Females have two different sex chromosomes (ZW) and males have two copies of same sex chromosome (ZZ).
Identify the type of heterogamety in each case, giving one example of each.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 57/1/1.

Hints

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

Hint 1

Heterogamety means one sex produces two different kinds of gametes.

Hint 2

In each case, ask which sex carries two different sex chromosomes (or only one).

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. Case I (XX–XO): the male produces two kinds of gametes (with X and without X), so this is male heterogamety.

    ½ mark

  2. Example: grasshopper (many insects).

    ½ mark

  3. Case II (ZW–ZZ): the female produces two kinds of gametes (Z and W), so this is female heterogamety.

    ½ mark

  4. Example: birds, e.g. hen.

    ½ mark

Answer: Case I: male heterogamety, e.g. grasshopper; Case II: female heterogamety, e.g. birds (hen)

Where the marks are

  • Case I identified as male heterogamety (½ mark)
  • Correct example such as grasshopper (½ mark)
  • Case II identified as female heterogamety (½ mark)
  • Correct example such as birds/hen (½ 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 paper2026 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.