In a typical dihybrid cross the `F_(2)` phenotypic ratio is

Options

A. `3:1`
B. `1:2:1`
C. `9:3:3:1`
D. `1:2:2:4:1:2:1:2:1`

Answer

To solve the question regarding the F2 phenotypic ratio in a typical dihybrid cross, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Dihybrid Cross**: A dihybrid cross involves two traits, each represented by two alleles. For example, consider two traits: seed color (Yellow - Y, Green - y) and seed shape (Round - R, Wrinkled - r).

2. **Identify Parent Genotypes**: In a typical dihybrid cross, one parent may have the genotype YYRR (homozygous yellow round) and the other may have the genotype yyrr (homozygous green wrinkled).

3. **Determine Gametes**: The gametes produced by the YYRR parent will be YR, and the gametes produced by the yyrr parent will be yr. When these gametes combine, the F1 generation will all be heterozygous (YyRr), exhibiting the dominant traits (yellow round).

4. **Self-Fertilization of F1 Generation**: When the F1 generation (YyRr) is self-fertilized, we can use a Punnett square to determine the F2 generation. The gametes from YyRr will be YR, Yr, yR, and yr.

5. **Construct the Punnett Square**: Set up a 4x4 Punnett square using the gametes from both parents:
- The rows represent the gametes from one parent (YyRr).
- The columns represent the gametes from the other parent (YyRr).

6. **Count the Phenotypes**: After filling in the Punnett square, we will find the following phenotypes:
- Yellow Round (YYRR, YYRr, YyRR, YyRr): 9
- Yellow Wrinkled (YYrr, Yyrr): 3
- Green Round (yyRR, yyRr): 3
- Green Wrinkled (yyrr): 1

7. **Calculate the Phenotypic Ratio**: The phenotypic ratio of the offspring in the F2 generation will be 9 (Yellow Round) : 3 (Yellow Wrinkled) : 3 (Green Round) : 1 (Green Wrinkled), which simplifies to 9:3:3:1.

8. **Select the Correct Answer**: Therefore, the correct F2 phenotypic ratio in a typical dihybrid cross is **9:3:3:1**.

### Final Answer:
The F2 phenotypic ratio in a typical dihybrid cross is **9:3:3:1**.