In polymeric gene action, the modified dihybrid phenotypic ratio in `F_(2)` generation is
(a) `9:3:3:1`
(b) `13:3`
(c) `9:6:1`
(d) `12:3:4`

Options

A. `9:3:3:1`
B. `13:3`
C. `9:6:1`
D. `12:3:4`

Answer

To solve the question regarding the modified dihybrid phenotypic ratio in the F2 generation due to polymeric gene action, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Dihybrid Cross**: A dihybrid cross involves two traits, each controlled by different genes. The typical phenotypic ratio in a dihybrid cross (when both genes assort independently) is 9:3:3:1.

2. **Identify Polymeric Gene Action**: Polymeric gene action occurs when two or more genes influence the same trait, leading to a modified phenotypic ratio. This means that the interaction of these genes can alter the expected 9:3:3:1 ratio.

3. **Determine the Modified Ratio**: In cases of polymeric gene action, the modified phenotypic ratios can vary. Common modified ratios include 9:6:1, 12:3:4, and 13:3, among others.

4. **Analyze the Options**:
- (a) 9:3:3:1 - This is the standard dihybrid ratio.
- (b) 13:3 - This is a modified ratio but not the most common one associated with polymeric gene action.
- (c) 9:6:1 - This is a recognized modified ratio due to polymeric gene action.
- (d) 12:3:4 - This is another modified ratio but not the one we are looking for in this context.

5. **Select the Correct Answer**: Based on the understanding of polymeric gene action and the analysis of the options, the correct answer is (c) 9:6:1.

### Final Answer:
The modified dihybrid phenotypic ratio in F2 generation due to polymeric gene action is **(c) 9:6:1**.