What is the ratio of one pair of contrasting character in `F_(2)` of a dihybrid ratio.

Options

A. `3:1`
B. `9:3:3:1`
C. `5:3`
D. `1:2:2:4:1:2:1:2:1`

Answer

To determine the ratio of one pair of contrasting characters in the F2 generation 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 'R' vs. wrinkled 'r') and seed color (yellow 'Y' vs. green 'y').

2. **Parental Generation (P)**:
In the parental generation, we can have two homozygous parents:
- Parent 1: Round Yellow (RRYY)
- Parent 2: Wrinkled Green (rryy)

3. **F1 Generation**:
When these two parents are crossed, all offspring (F1 generation) will be heterozygous for both traits:
- F1: RrYy (Round Yellow)

4. **F2 Generation**:
To obtain the F2 generation, we cross two F1 individuals (RrYy x RrYy). This will result in a phenotypic ratio.

5. **Phenotypic Ratio Calculation**:
The phenotypic ratio of the F2 generation from a dihybrid cross is typically 9:3:3:1. This means:
- 9 Round Yellow
- 3 Round Green
- 3 Wrinkled Yellow
- 1 Wrinkled Green

6. **Identifying One Pair of Contrasting Characters**:
If we focus on one pair of contrasting characters, such as seed shape (Round vs. Wrinkled), we can see that:
- Round (R_) = 9 (from Round Yellow and Round Green)
- Wrinkled (rr) = 3 (from Wrinkled Yellow and Wrinkled Green)

7. **Final Ratio**:
Therefore, the ratio of one pair of contrasting characters (Round vs. Wrinkled) in the F2 generation is 3:1.

### Final Answer:
The ratio of one pair of contrasting characters in the F2 generation of a dihybrid cross is **3:1**.

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