Q1. [3]
Table showing Mendelian cross results:
Parents: A pea plant with red flowers was crossed with a pea plant with white flowers.
F1: 30 seeds were sown and all bore plants with red flowers.
F2: 44 seeds were sown, 33 plants bore red flowers and 11 plants bore white flowers.
Study the given table and answer the following questions :
- (a) Depict the information given in the table in the form of a cross.
- (b) Deduce the F2 phenotypic ratio/F2 ratio showing external look as well as genotypic/genetic makeup ratio.
Previously asked in CBSE board exam
2026 31/4/1 Q14
Generated by claude-sonnet-4-6 · 2026-06-15 06:51 · grounding stimulus
Model Answer
(a) Cross:
Let Red (R) be dominant over white (r).
P: RR (Red) × rr (White)
F₁: All Rr (Red)
F₁ × F₁: Rr × Rr
F₂:
| | R | r |
|--|--|--|
| R | RR | Rr |
| r | Rr | rr |
F₂: RR : Rr : rr → 1 : 2 : 1
(b) F₂ Ratios:
- Phenotypic ratio (external appearance): Red : White = 3 : 1 (33 red : 11 white, approximately 3:1)
- Genotypic ratio (genetic makeup): RR : Rr : rr = 1 : 2 : 1
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Explanation
- (a) CBSE expects the actual Punnett square or gamete cross notation. Show P, F₁, and F₁×F₁ steps clearly using dominant (capital) and recessive (small) letters.
- (b) Two separate ratios must be stated: phenotypic (3:1) and genotypic (1:2:1). Examiners deduct marks if either is missing. The 33:11 from the table confirms the 3:1 ratio.
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