Q1. [2] medium initial-understanding
In Mendel's experiment, when F1 tall plants were self-pollinated, one quarter of the F2 offspring were short. What does the reappearance of the short trait in F2 prove about the F1 tall plants?
Generated by claude-sonnet-4-6 · 2026-06-26 01:02 · grounding rag
Model Answer
The reappearance of short plants in F₂ proves that the F₁ tall plants were not pure tall — they had inherited both the tallness and shortness traits. The shortness trait was present but not expressed (recessive) in F₁. This shows that two copies of a factor (gene) controlling a trait are present, where 'T' (tallness) is dominant and 't' (shortness) is recessive, giving F₁ genotype Tt.
Source: Chapter 8, Section 8.2.2
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Explanation
- The key point examiners want: F₁ plants carried both traits (Tt), but only expressed the dominant one.
- Second key point: shortness is recessive — it reappears only when both copies are 't' (tt) in F₂.
- Mention dominant/recessive terminology and the idea of two copies of genes — these fetch marks.
- Avoid saying "the trait disappeared in F₁" without explaining it was hidden, not gone.