Two nonallelic genes produces the new phenotype when present together but fail to do so independently then it is called : -

Options

A. Epistasis
B. Polygene
C. Non complimentry gene
D. Complimentry gene

Answer

To solve the question, "Two nonallelic genes produce a new phenotype when present together but fail to do so independently then it is called:", we can follow these steps:

### Step 1: Understand the Terms
- **Nonallelic Genes**: These are genes located at different loci on a chromosome that do not have alternative forms (alleles) for the same trait.
- **Phenotype**: The observable characteristics or traits of an organism.

### Step 2: Analyze the Options
- **A. Epistasis**: This refers to the interaction between genes where the effect of one gene is masked or suppressed by another gene. This does not fit the description of producing a new phenotype when both genes are present.

- **B. Polygen**: This term is not commonly used in genetics. It might refer to polygenic inheritance, where multiple genes contribute to a single trait, but it does not fit the scenario described.

- **C. Non-complementary Genes**: This refers to a situation where the recessive alleles of different gene loci fail to complement each other. This does not align with the description of producing a new phenotype when both genes are present.

- **D. Complementary Genes**: This is the correct term. Complementary genes are nonallelic genes that work together to produce a new phenotype. When both genes are present, they interact to create a new trait, but if either gene is absent, the new phenotype does not manifest.

### Step 3: Conclusion
Based on the analysis, the correct answer is **D. Complementary genes**. These genes produce a new phenotype only when both are present together, which aligns with the question.

### Final Answer
**D. Complementary genes**

---