List two differences between dominant traits and recessive traits. What percentage of pea plants in the F2 generation were with yellow seeds when Mendel crossed yellow (YY) and green coloured (yy) seeds ?
Generated by claude-sonnet-4-6 · 2026-06-15 06:52 · grounding rag
Model Answer
Differences between Dominant and Recessive Traits:
| Dominant Trait | Recessive Trait |
|---|---|
| Expressed when even one copy of the gene is present (e.g., Tt or TT) | Expressed only when both copies are the same recessive gene (e.g., tt) |
| Masks the recessive trait | Gets masked/suppressed in the presence of the dominant gene |
Percentage of yellow-seeded plants in F2 generation:
Cross: YY × yy → F1: Yy (all yellow)
F1 × F1: Yy × Yy → F2: YY : Yy : yy = 1 : 2 : 1
Plants with yellow seeds (YY + Yy) = 75%
Source: Heredity, Section 8.2.2
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Explanation
- Give exactly two differences — one mark each.
- The cross/calculation carries one mark; show the F2 ratio clearly and state 75%. Examiners look for the Punnett logic (F1 = Yy, F2 ratio) and the final percentage. Writing just "75%" without the cross loses marks.
- Remember: yellow (Y) is dominant over green (y), so YY and Yy both appear yellow.