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Science — CBSE Class 10 board question

Q1. [1]
In an experiment with pea plants, a pure tall plant (TT) is crossed with a pure short plant (tt). The ratio of pure tall plant to pure short plants in F₂ generation will be
  1. (a) 1 : 3
  2. (b) 3 : 1
  3. (c) 1 : 1
  4. (d) 2 : 1
Previously asked in CBSE board exam
2023 31/6/1 Q9
Generated by claude-sonnet-4-6 · 2026-06-15 06:54 · grounding rag
Model Answer

(c) 1 : 1

In F₂, the genotypes are TT : Tt : tt = 1 : 2 : 1. Pure tall (TT) : pure short (tt) = 1 : 1.

Explanation

Students often confuse the phenotypic ratio (3 tall : 1 short) with the genotypic ratio. The question asks for pure plants only — TT and tt — both present in 1 out of 4 offspring each, giving 1 : 1. Hybrid tall (Tt) plants are tall in appearance but not pure, so they are excluded from the count.

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Previous-year CBSE Grade 10 board exam questions, organised by subject and chapter, each with a model answer — free to read and print.