In Mendel's experiments, the dihybrid phenotypic ratio was 

Key Points

• Gregor Mendel is known as the Father of Genetics as he gave the Principles of Inheritance that formed the basis of genetics.
• His experiments involved plant hybridizations on garden pea plant.
• Dihybrid cross - is a cross or hybridization between 2 parents differing in 2 traits.
• Each of the traits had 2 distinct phenotypic characters - one dominant, one recessive.

Explanation:

• Mendel chose 2 traits:
  • Seed shape - Round (dominant) and wrinkled (recessive).
  • Seed color - Yellow (dominant) and green (recessive).
• From the cross between these 2 parental generation plants, he obtained the F1 generation where all plants had Round, Yellow seeds.
• These F1 plants were self-fertilized to get the F2 generation.
• The phenotypic and genotypic ratios are then observed from the F2 generation.

Important Points

• The characters can be expressed in homozygous or heterozygous conditions:
  • Yellow - YY, Yy
  • Green - yy
  • Round - RR, Rr
  • Wrinkled - rr
• The characters in the F2 generation were expressed in the proportions given above.
• Thus, we can get the phenotypic ratio of this dihybrid cross as:

9 (Round, Yellow) : 3 (Round, Green) : 3 (Wrinkled, Yellow): 1 (Wrinkled, Green)

• We get 4 phenotypes from a dihybrid cross.