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Study the pedigree chart… (Class 12 Biology 2025, Q20)

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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 20

Set in the CBSE Class 12 board exam of 2025, paper 57/1/1, section B, question 20, for 2 marks. Try it first; the hints and our step-by-step solution are below.

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

Study the pedigree chart given below, showing the inheritance pattern of blood group in a family :

Answer the following questions :

  1. (a)

    Give the possible genotypes of individual 1 and 2.

    0 marks
  2. (b)

    Which antigen or antigens will be present on the plasma membranes of the R.B.Cs of individuals '5' and '8' ?

    0 marks

Figure in the paper: Pedigree. Parents: 1 (male, blood group B) and 2 (female, A). Generation I children: 3 (female, B) married to 4 (male, A); 5 (male, AB); 6 (female, B); 7 (male, A). Generation II (children of 3 and 4): 8 (female, O) and 9 (male, B). 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

Look at the children of 1 and 2. Can a child with group A come from a group B father who is homozygous?

Hint 2

Blood group O means genotype . Which antigen does the allele produce?

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) Individual 1 (blood group B): genotype . Their child 7 has blood group A. That child must get from mother 2 and therefore from father 1.

    ½ mark

  2. Individual 2 (blood group A): genotype . Their child 3 has blood group B. That child gets from father 1 and must get from mother 2.

    ½ mark

  3. (b) Individual 5 (AB): both antigen A and antigen B are present on the RBC surface, because and are co-dominant.

    ½ mark

  4. **Individual 8 (O, ): neither antigen A nor antigen B** is present on the RBCs.

    ½ mark

Answer: (a) 1 = , 2 = ; (b) 5 has both A and B antigens; 8 has neither.

Where the marks are

  • Genotype of 1 as (½ mark)
  • Genotype of 2 as (½ mark)
  • Individual 5 has both A and B antigens (½ mark)
  • Individual 8 has no A or B antigen (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 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.