Which of the following depicts phenotypic ratio of dihybrid cross?

Options

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

Answer

To determine the phenotypic ratio of a 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, let’s consider two traits: seed shape (round vs. wrinkled) and seed color (yellow vs. green). The alleles can be represented as R (round), r (wrinkled), Y (yellow), and y (green).

2. **Determine Parental Genotypes**: For a typical dihybrid cross, we can take two homozygous parents. For example, one parent could be RRYY (round yellow) and the other rryy (wrinkled green).

3. **F1 Generation**: When these two parents are crossed, all offspring in the F1 generation will be heterozygous for both traits (RrYy), displaying the dominant phenotypes (round yellow).

4. **F2 Generation**: To find the phenotypic ratio, we need to cross the F1 generation (RrYy x RrYy). This can be done using a Punnett square, which will help visualize the combinations of alleles.

5. **Construct the Punnett Square**: Create a 4x4 Punnett square to represent the combinations of the alleles from the two parents. The rows and columns will represent the gametes from each parent.

6. **Count the Phenotypes**: After filling in the Punnett square, count the different phenotypic combinations:
- Round Yellow (RY): 9
- Round Green (Rg): 3
- Wrinkled Yellow (rY): 3
- Wrinkled Green (rg): 1

7. **Determine the Phenotypic Ratio**: The resulting phenotypic ratio from the dihybrid cross is 9:3:3:1.

8. **Select the Correct Option**: Based on the options provided, the correct answer is option B: 9:3:3:1.

### Final Answer:
The phenotypic ratio of a dihybrid cross is **9:3:3:1** (Option B).

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