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Mendel crossed pure tall pea… (Class 10 Science 2024, Q30)

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ScienceCBSE Class 10 · Board exam 2024, set 31/5/1 · 3 marks · Short answer

CBSE Class 10 Science 2024: question 30

Set in the CBSE Class 10 board exam of 2024, paper 31/5/1, section C, question 30, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q30 · 3 marks · Short answerHeredity

Mendel crossed pure tall pea plants (TT) with pure short pea plants (tt) and obtained progeny. When the plants of progeny were self-pollinated, plants of progeny were obtained.

  1. (a)

    What did the plants of progeny look like? Give their gene combination.

    1 mark
  2. (b)

    Why could the gene for shortness not be expressed in plants of progeny?

    1 mark
  3. (c)

    Write the ratio of the plants obtained in progeny and state the conclusion that can be drawn from this experiment.

    1 mark

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 31/5/1.

Hints

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

Hint 1

Each plant receives one factor from each parent. Write down which two factors it gets.

Hint 2

Self-cross Tt × Tt in a checkerboard and count how many offspring have at least one T.

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) All the plants were tall;

    ½ mark

  2. their gene combination is Tt.

    ½ mark

  3. (b) The gene for shortness (t) is recessive. In the presence of the dominant gene T it cannot express itself, so Tt plants look tall.

    1 mark

  4. (c) ratio: Tall : Short = 3 : 1 (genotypes TT : Tt : tt = 1 : 2 : 1).

    ½ mark

  5. Conclusion: the tall trait is dominant and the short trait is recessive. The recessive trait, hidden in , is not lost and reappears in .

    ½ mark

Answer: (a) All tall, Tt; (b) shortness is recessive and is masked by dominant T; (c) Tall : Short = 3 : 1, so tallness is dominant and shortness recessive.

Where the marks are

  • States that all plants are tall (½ mark)
  • Gives the genotype Tt (½ mark)
  • Explains that t is recessive and masked by T (1 mark)
  • Gives the ratio 3 : 1 (½ mark)
  • Concludes tall is dominant and short is recessive (½ mark)

Revise the chapter

Practise this chapterBoard-style questions from Heredity, one at a time, marked against the answer key and marking points.Back to the full paper2024 board paper, set 31/5/1: 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.