The ratio 9:7 is produced due to -

Options

A. complementary genes
B. supplementary genes
C. lethal genes
D. epistatic genes

Answer

### Step-by-Step Solution:

1. **Understanding the Ratio**: The ratio 9:7 is a phenotypic ratio that arises from a specific type of genetic interaction. This ratio is typically associated with complementary gene action.

2. **Complementary Genes**: Complementary genes are two different genes that work together to produce a particular phenotype. For the 9:7 ratio to occur, both genes must be present in their dominant forms.

3. **Genetic Combinations**: In a typical dihybrid cross involving two complementary genes (let's denote them as gene R and gene Y), the possible combinations of alleles can be represented as:
- RRYY (dominant for both genes)
- RRYy (dominant for R, recessive for Y)
- RrYY (dominant for Y, recessive for R)
- RrYy (dominant for both)
- Rryy (recessive for R, dominant for Y)
- rrYY (recessive for Y, dominant for R)
- rryy (recessive for both)

4. **Phenotypic Outcomes**: The phenotypic outcomes of these combinations lead to:
- 9 individuals showing the dominant phenotype (where at least one dominant allele from both genes is present).
- 7 individuals showing a different phenotype (where at least one gene is recessive).

5. **Conclusion**: Therefore, the 9:7 ratio is produced due to the interaction of complementary genes, where both genes must be present in their dominant forms to express the dominant phenotype.

### Final Answer:
The ratio 9:7 is produced due to complementary gene interaction.

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