Q1. [3] medium initial-understanding
In Mendel's cross between tall and short pea plants, all F1 plants were tall, but short plants reappeared in the F2 generation. What does this reappearance tell us about the fate of the 'shortness' trait in the F1 generation? Name the terms used for the two traits involved.
Generated by claude-sonnet-4-6 · 2026-06-26 01:02 · grounding rag
Model Answer
The reappearance of short plants in F2 shows that the 'shortness' trait was not lost or destroyed in the F1 generation — it was merely hidden (unexpressed). The F1 plants inherited both the tallness and shortness factors, but only tallness was expressed. When F1 plants self-pollinated, the shortness factor was transmitted to the next generation and reappeared in ¼ of F2 plants.
- The trait that gets expressed (tallness) is called the dominant trait.
- The trait that remains hidden (shortness) is called the recessive trait.
Source: Chapter 8, Section 8.2.2 – Rules for the Inheritance of Traits
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Explanation
- The key idea examiners expect: the recessive trait is inherited but not expressed in F1 — it is carried in the Tt genotype. Students often incorrectly say the trait "disappeared" or "mixed."
- Always name both terms (dominant and recessive) with examples — this question specifically asks for both, so leaving either out loses marks.
- The 3-mark split is roughly: 1 mark for explaining shortness was hidden (not lost), 1 mark for it being carried in F1 and reappearing in F2, 1 mark for correctly naming dominant and recessive with the correct trait matched to each term.