Ratio of complementary genes is

Options

A. `9 : 3 : 4`
B. `12 : 3 : 1`
C. `9 : 3 : 3 : 4`
D. `9 : 7`

Answer

To solve the question regarding the ratio of complementary genes, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Complementary Genes**:
- Complementary genes are two non-allelic genes that interact to produce a specific phenotype. Each gene contributes to the expression of a trait, and when both are present in their dominant forms, they produce a new trait.

2. **Mendelian Ratios**:
- In a typical dihybrid cross involving two genes, the expected Mendelian ratio for the phenotypes is 9:3:3:1. This ratio represents the different combinations of dominant and recessive alleles from both genes.

3. **Effect of Complementation**:
- When two complementary genes are involved, the interaction between the dominant alleles leads to a modification of the expected Mendelian ratio. Instead of the typical 9:3:3:1 ratio, the presence of both dominant alleles results in a new phenotype.

4. **Final Ratio for Complementary Genes**:
- The modified ratio for complementary genes is 9:7. This means that when both genes are present in their dominant forms, they complement each other, leading to a specific phenotype, while the absence of either dominant allele results in a different phenotype.

5. **Conclusion**:
- Therefore, the ratio of complementary genes is 9:7.

### Final Answer:
The ratio of complementary genes is **9:7** (Option D).

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