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Answer the following. (Class 12 Biology 2026, Q23)

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BiologyCBSE Class 12 · Board exam 2026, set 57/1/1 · 3 marks · Short answer

CBSE Class 12 Biology 2026: question 23

Set in the CBSE Class 12 board exam of 2026, paper 57/1/1, section C, question 23, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q23 · 3 marks · Short answerCompetency-basedPrinciples of Inheritance and Variation

Answer the following.

  1. (a)

    What is pedigree analysis ? Mention its importance in human genetics. (2 pts.) (1 + 1)

    0 marks
  2. (b)

    Analyse the following pedigree and write the
    (i) Pattern of inheritance. (½)
    (ii) Give one example of disease showing such an inheritance pattern. (½)

    0 marks

Figure in the paper: Pedigree chart: a normal male and normal female parents at top; their six children in second row: normal male, affected male (filled), normal male (married to a normal female), the normal female, affected female (filled), normal male. The normal male–normal female couple has three children: an affected male (filled), and two normal females. See it in the official paper.

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

Why can human geneticists not do test crosses? What do they study instead?

Hint 2

Look at what happens when unaffected parents have affected children.

Hint 3

Check the sex of the affected children against the phenotype of their father.

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) Pedigree analysis is the study of how a trait is inherited over several generations of a family, using a family tree drawn with standard symbols.

    1 mark

  2. Importance: controlled crosses are not possible in humans, so pedigree analysis is used to trace the inheritance of a trait, abnormality or genetic disease. It shows whether the trait is dominant or recessive, autosomal or sex-linked, and helps in genetic counselling.

    1 mark

  3. (b)(i) Normal parents have affected children, so the trait is recessive and both parents are carriers. An affected daughter is born to a normal father; this rules out X-linked recessive inheritance, because the father would then have to be affected. The pattern is therefore autosomal recessive.

    ½ mark

  4. (ii) Example: sickle-cell anaemia (also phenylketonuria or thalassemia).

    ½ mark

Answer: (a) Study of inheritance of a trait over several generations of a family; used to trace the inheritance of traits and diseases; (b)(i) autosomal recessive; (ii) sickle-cell anaemia

Where the marks are

  • Correct definition of pedigree analysis (1 mark)
  • Importance: tracing the inheritance of a trait or disease in humans (1 mark)
  • Autosomal recessive (½ mark)
  • Correct example, e.g. sickle-cell anaemia/phenylketonuria/thalassemia (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.