The `F_2` dihybrid ratio 9 : 3 : 4 is explained on the basis of

Options

A. Epistatic gene
B. Supplementary gene
C. Allelic interaction
D. Complementary gene interaction

Explanation

To solve the question regarding the `F2` dihybrid ratio of 9:3:4, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understand the Dihybrid Cross**: A dihybrid cross involves two traits, each controlled by different genes. When two heterozygous individuals are crossed (e.g., AaBb x AaBb), the expected phenotypic ratio in the `F2` generation is typically 9:3:3:1 if the genes assort independently.

2. **Identify the Given Ratio**: The question states that the `F2` dihybrid ratio is 9:3:4. This is different from the typical 9:3:3:1 ratio, indicating that there is some interaction between the genes involved.

3. **Determine the Type of Gene Interaction**: The 9:3:4 ratio is indicative of supplementary gene interaction. In supplementary gene interaction, two different genes affect the same trait, and the presence of dominant alleles from both genes results in a different phenotype.

4. **Explain Supplementary Gene Interaction**: In this interaction, if both dominant alleles are present, a specific phenotype is expressed. If only one dominant allele from either gene is present, a different phenotype is produced. If neither dominant allele is present, another phenotype is expressed. This leads to three distinct phenotypic outcomes, which correspond to the 9:3:4 ratio.

5. **Conclusion**: Therefore, the `F2` dihybrid ratio of 9:3:4 is explained on the basis of supplementary gene interaction.

### Final Answer:
The `F2` dihybrid ratio of 9:3:4 is explained on the basis of supplementary gene interaction.

---