Q1. [2] § 8.2.2 Rules for the Inheritance of Traits – Mendel's Contributions
Using height (tallness / dwarfness) of a plant as an example, show that genes control the characteristics or traits in an organism.
Previously asked in CBSE board exam
2022 31/4/1 Q3 (main)
Generated by claude-sonnet-4-6 · 2026-06-15 06:54 · grounding rag
Model Answer
In pea plants, height is controlled by a gene with two forms (alleles): 'T' (tallness) and 't' (dwarfness). When a tall plant (TT) is crossed with a short plant (tt), all F₁ plants are tall (Tt). When F₁ plants self-pollinate, F₂ plants are tall (TT/Tt) or short (tt) in a 3:1 ratio. This shows that the gene 'T' or 't' directly determines whether the plant is tall or dwarf — proving genes control traits.
Source: Chapter 8, Section 8.2.2 – Rules for the Inheritance of Traits
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Explanation
- Examiners want you to mention: alleles (T and t), F₁ result (all tall), F₂ result (3 tall : 1 short), and the conclusion that genes control traits.
- State that 'T' is dominant (one copy sufficient) and 'tt' gives short plant (recessive — both copies needed).
- Avoid lengthy diagrams unless asked; a brief cross notation (TT × tt → Tt) is enough to support the explanation within the word limit.
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