The phenotypic ratio in the `F_2` generation of dihybrid cross is

Options

A. `9:3:3:1`
B. `1:2:2:4:1:2:1:2:1 `
C. `7:1:1:7`
D. `12: 8:4 `

Answer

To determine the phenotypic ratio in the F2 generation of a dihybrid cross, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Dihybrid Cross**:
A dihybrid cross involves two traits, each represented by two alleles. For example, we can consider the traits of seed shape (round vs. wrinkled) and seed color (yellow vs. green). Let's denote:
- Round (R) is dominant over wrinkled (r)
- Yellow (Y) is dominant over green (y)

2. **Establish the Parental Generation (P)**:
We start with two homozygous parents:
- Parent 1: Round Yellow (RRYY)
- Parent 2: Wrinkled Green (rryy)

3. **Determine the F1 Generation**:
When we cross these two parents, all offspring in the F1 generation will be heterozygous for both traits:
- F1 Generation: All offspring will be Round Yellow (RrYy).

4. **Gamete Formation**:
Each F1 individual can produce four types of gametes due to independent assortment:
- RY (Round Yellow)
- Ry (Round Green)
- rY (Wrinkled Yellow)
- ry (Wrinkled Green)

5. **Set Up the F2 Generation**:
To find the F2 generation, we perform a cross between two F1 individuals (RrYy x RrYy). We can use a Punnett square to visualize the combinations of gametes.

6. **Construct the Punnett Square**:
The Punnett square for the dihybrid cross will be a 4x4 grid, where each row and column represents the gametes from each parent:
```
RY Ry rY ry
-------------------------
RY | RRYY | RRYy | RrYY | RrYy
-------------------------
Ry | RRYy | RRyy | RrYy | Rryy
-------------------------
rY | RrYY | RrYy | rrYY | rrYy
-------------------------
ry | RrYy | Rryy | rrYy | rryy
```

7. **Count the Phenotypes**:
Now we count the phenotypes based on the combinations:
- Round Yellow (RRYY, RRYy, RrYY, RrYy): 9
- Round Green (RRyy, Rryy): 3
- Wrinkled Yellow (rrYY, rrYy): 3
- Wrinkled Green (rryy): 1

8. **Calculate the Phenotypic Ratio**:
The phenotypic ratio in the F2 generation is therefore:
- Round Yellow : Round Green : Wrinkled Yellow : Wrinkled Green = 9 : 3 : 3 : 1

9. **Conclusion**:
The correct answer to the question is that the phenotypic ratio in the F2 generation of a dihybrid cross is **9:3:3:1**.