In a cross between red coloured and white coloured flowers, when plants with red coloured flowers of F1 generation were self pollinated, plants of F2 generation were obtained in which 75% of plants were with red flowers and 25% plants were with white flowers. Explain the inheritance of traits in the above cross with the help of a flow chart only along with the ratio of plants obtained.
Generated by claude-sonnet-4-6 · 2026-06-15 06:54 · grounding rag
Model Answer
Cross between Red (RR) × White (rr) flowers:
$$RR \times rr$$
$$\downarrow$$
$$\text{F}_1: \text{All } Rr \text{ (Red flowers)}$$
$$\downarrow \text{(Self-pollination)}$$
$$\text{F}_2: RR : Rr : rr = 1:2:1$$
Ratio: 3 Red (RR + Rr) : 1 White (rr) → 3:1
Red (R) is the dominant trait; White (r) is the recessive trait.
Source: Chapter 8 – Heredity, Section 8.2.2
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Explanation
- The examiner wants a flow chart format showing P, F₁, and F₂ generations — not a paragraph. Draw the cross clearly with arrows.
- Write the genotypes (RR, Rr, rr) alongside phenotypes.
- Always state the 3:1 phenotypic ratio and identify which trait is dominant/recessive — these are the likely marking points for 2 marks.
- Since red flowers appear in F₁, red is dominant; white reappears in F₂, confirming it is recessive.