State Mendel’s law of independent assortment and illustrate it with a cross between two heterozygous pea plants for seed shape (Rr) and seed colour (Yy).
Answer
Mendel’s law of independent assortment says that alleles of different genes segregate independently during gamete formation, so the genotype of one trait does not affect the genotype of another. In the Rr × Yy cross, the two genes assort independently producing a 9:3:3:1 phenotypic ratio in the F2 generation.
Step-by-step solution
- Write the statement of the law: alleles of different genes segregate independently during gamete formation.
- Explain that independence means the allele received for one trait does not influence the allele received for another trait.
- Identify the two heterozygous traits: seed shape (Rr) and seed colour (Yy).
- List the possible gametes from each parent: RY, Ry, rY, ry.
- Construct a 4×4 Punnett square using these gametes.
- Count the phenotypic classes: 9 round‑yellow, 3 round‑green, 3 wrinkled‑yellow, 1 wrinkled‑green, giving a 9:3:3:1 ratio.
Common mistake: Assuming linked genes give a 9:3:3:1 ratio without checking linkage
Concept tested: Law of independent assortment
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