Mendel worked out the rules of heredity by working on garden pea using a number of visible contrasting characters. He conducted several experiments by making a cross with one or two pairs of contrasting characters of pea plant. On the basis of his observations he gave some interpretations which helped to study the mechanism of inheritance.
Generated by claude-sonnet-4-6 · 2026-06-15 06:53 · grounding stimulus
Model Answer
(i) In F₁ plants, Mendel observed:
- All plants were tall (no short plants appeared).
- Only one trait (tallness) was expressed; shortness was hidden.
(ii) A dominant trait is the one that expresses itself in F₁ generation (e.g., tallness), whereas a recessive trait is the one that remains hidden in F₁ but reappears in F₂ generation (e.g., shortness).
(iii) Mendel obtained F₂ generation by self-pollination of F₁ plants (RrYy × RrYy).
The ratio of parental combinations (Round Yellow : Wrinkled Green) in F₂ = 9 : 3 : 3 : 1 overall; parental types (RRYY and rryy types) appeared in ratio 9 : 1 among combinations.
Conclusion: The two pairs of traits assorted independently of each other — this is the Law of Independent Assortment.
Source: Heredity and Evolution, Mendel's Laws of Inheritance
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Explanation
- For (i), examiners expect two distinct observations about F₁ — all tall, and shortness hidden. One mark requires both points briefly stated.
- For (ii), a clear one-line contrast with examples scores full marks. Avoid long definitions.
- For (iii), three things are tested: method (self-pollination/selfing of F₁), the ratio (9:3:3:1 and parental combinations 9 round yellow : 3 wrinkled yellow : 3 round green : 1 wrinkled green, parental combos ratio 9:1), and the conclusion (Law of Independent Assortment). Cover all three for full 2 marks.