In order to trace the inheritance of traits Mendel crossed pea plants having one contrasting character or a pair of contrasting characters. When he crossed pea plants having round and yellow seeds with pea plants having wrinkled and green seeds, he observed that no plants with wrinkled and green seeds were obtained in the F₁ generation. When the F₁ generation pea plants were cross-bred by self-pollination, the F₂ generation had seeds with different combinations of shape and colour also.
Generated by claude-sonnet-4-6 · 2026-06-15 06:54 · grounding stimulus
Model Answer
(a) Two pairs of contrasting characters used by Mendel (other than seed shape and colour):
- Tall plant vs. Dwarf plant
- Inflated pod vs. Constricted pod
(b) A dominant trait is the one that expresses itself in the F₁ generation (e.g., round, yellow seeds). A recessive trait is the one that remains hidden in F₁ but reappears in F₂ (e.g., wrinkled, green seeds).
(c) The F₂ generation shows seeds in the ratio 9 : 3 : 3 : 1
(9 Round Yellow : 3 Round Green : 3 Wrinkled Yellow : 1 Wrinkled Green).
Interpretation: The traits of seed shape and seed colour are independently inherited; they segregate independently during gamete formation and recombine freely. This is Mendel's Law of Independent Assortment.
Source: Heredity and Evolution, Mendel's Contribution
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Explanation
- (a) Any two of the seven pairs Mendel used are acceptable; tall/dwarf and inflated/constricted pod are safe choices.
- (b) The key distinction is expression in F₁ vs. hidden in F₁ but visible in F₂. Use the words "expresses" and "remains hidden/suppressed."
- (c) The 9:3:3:1 ratio is the standard dihybrid ratio — must be stated with the full description of each class. The interpretation must mention independent assortment; examiners look for this conclusion explicitly.