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Mendel crossed a pure tall… (Class 10 Science 2023, Q23)

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ScienceCBSE Class 10 · Board exam 2023, set 31/2/1 · 2 marks · Very short answer

CBSE Class 10 Science 2023: question 23

Set in the CBSE Class 10 board exam of 2023, paper 31/2/1, section B, question 23, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q23 · 2 marks · Very short answerHeredity

Mendel crossed a pure tall pea plant (TT) with a pure short pea plant (tt) and obtained all tall plants in generation.

  1. (a)

    What is the gene combination present in the plants of generation ?

    1 mark
  2. (b)

    Give reason why only tall plants are observed in progeny.

    1 mark
  3. (c)

    What will be the ratio of the plants obtained in the generation when plants are self-pollinated ?

    1 mark

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 31/2/1.

Hints

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

Hint 1

Write the gametes each parent can produce.

Hint 2

If a plant carries both T and t, which one shows up?

Hint 3

Draw a 2 × 2 checkerboard for Tt × Tt and count the plants with 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) The cross is TT × tt. The tall parent gives gamete T and the short parent gives gamete t, so every plant is Tt (heterozygous).

    ½ mark

  2. (b) The trait for tallness (T) is dominant over the trait for shortness (t). In Tt plants only the dominant trait is expressed, and the recessive trait stays hidden, so all plants are tall.

    1 mark

  3. (c) Selfing Tt × Tt gives TT : Tt : tt = 1 : 2 : 1. So in , Tall : Short = 3 : 1.

    ½ mark

Answer: (a) Tt; (b) tallness is dominant over shortness, so only it is expressed; (c) Tall : Short = 3 : 1

Where the marks are

  • Gene combination Tt (½ mark)
  • Reason: tall trait is dominant, so only it is expressed in F₁ (1 mark)
  • F₂ ratio Tall : Short = 3 : 1 (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 paper2023 board paper, set 31/2/1: 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.