How many plants with the double dominant character are appear in mendel's dihybrid ratio of F2 generation?

Mendel's Dihybrid Ratio in the F2 Generation

In Mendel's dihybrid cross, he studied the inheritance of two different traits simultaneously. He chose pea plants and conducted experiments by crossing pure-breeding parental plants that differed in two traits, such as flower color (purple or white) and seed shape (round or wrinkled). Mendel observed the F1 generation and then allowed them to self-pollinate to obtain the F2 generation.

Dihybrid Cross and the Law of Independent Assortment

Mendel's experiments led to the formulation of the Law of Independent Assortment. According to this law, during gamete formation, the alleles for different traits segregate independently of each other. As a result, the combinations of alleles for one trait do not influence the combinations for another trait.

Expected Phenotypic Ratio in the F2 Generation

When Mendel crossed the F1 generation plants, he observed a phenotypic ratio of 9:3:3:1 in the F2 generation. This ratio can be further explained as follows:

1. 9 plants with both dominant traits: These plants have both dominant alleles for both traits. For example, if the dominant alleles for flower color are represented by "P" and for seed shape by "R", then the genotype of these plants would be PPRR.

2. 3 plants with dominant trait for one trait and recessive trait for the other: These plants have one dominant allele and one recessive allele for each trait. For example, the genotype of these plants could be PpRR, PPrr, or Pprr.

3. 3 plants with dominant trait for one trait and recessive trait for the other: These plants also have one dominant allele and one recessive allele for each trait, but the alleles are switched compared to the previous category. For example, the genotype of these plants could be PPrr, PpRR, or Pprr.

4. 1 plant with both recessive traits: These plants have both recessive alleles for both traits. For example, if the recessive alleles for flower color are represented by "p" and for seed shape by "r", then the genotype of this plant would be pprr.

Conclusion

In Mendel's dihybrid cross, the F2 generation follows a phenotypic ratio of 9:3:3:1. Among these, 9 plants have both dominant traits, which means they have the double dominant characters. These plants possess the dominant alleles for both traits and exhibit the dominant phenotypes for flower color and seed shape.