CBSE · Class 10 · Science · HeredityExplain Mendel's law of independent assortment with the help of a dihybrid cross. Also, work out the phenotypic and genotypic ratios of the F2 generation taking seed shape (round/wrinkled) and seed color (yellow/green) as the two traits.

Introduction to Independent Assortment\nMendel's Law of Independent Assortment states that when two pairs of traits are combined in a hybrid, segregation of one pair of characters is independent of the other pair of characters at the time of gamete formation. This law is best understood using a dihybrid cross.

Experiment and Traits\nGregor Mendel crossed pea plants with two contrasting pairs of traits:

• Seed Shape: Round (R) is dominant over wrinkled (r).
• Seed Color: Yellow (Y) is dominant over green (y).

Cross Details

1. Parental Generation (P): Pure breeding round yellow seeds (RRYY) were crossed with pure breeding wrinkled green seeds (rryy).
2. First Filial Generation (F1): The F1 generation plants all had round yellow seeds with the genotype RrYy, demonstrating the dominance of round and yellow traits.
3. Self-pollination of F1: When F1 generation plants (RrYy) were self-pollinated, gametes with combinations of alleles (RY, Ry, rY, ry) were formed independently.

Punnett Square and F2 Generation\nA 16-square Punnett square is used to determine the F2 progeny:

• Gametes from male and female: RY, Ry, rY, ry.
• Phenotypic Combinations:
  • Round and Yellow = 9
  • Round and Green = 3
  • Wrinkled and Yellow = 3
  • Wrinkled and Green = 1

Phenotypic and Genotypic Ratios

• Phenotypic Ratio: 9 : 3 : 3 : 1
• Genotypic Ratio: A more complex ratio of 1:2:1:2:4:2:1:2:1, reflecting the independent assortment of alleles during gamete production.