Genotypic ratio of a dihybrid cross is

Options

A. `12:3:1`
B. `15:1`
C. `1:2:1`
D. `1:2:2:4:1:2:1:2:1`

Answer

To determine the genotypic ratio of a dihybrid cross, we can follow these steps:

### Step 1: Understand the Basics of Dihybrid Cross
A dihybrid cross involves two traits, each with two alleles. For example, let’s consider the traits for seed shape (Round, R, dominant over Wrinkled, r) and seed color (Yellow, Y, dominant over Green, y).

### Step 2: Determine the Parental Genotypes
Assume we are crossing two heterozygous parents for both traits:
- Parent 1: RrYy (Round Yellow)
- Parent 2: RrYy (Round Yellow)

### Step 3: Set Up a Punnett Square
To find the genotypic ratio, we can set up a 4x4 Punnett square since each parent can produce four types of gametes (RY, Ry, rY, ry).

### Step 4: Fill in the Punnett Square
The gametes from each parent will combine in the following way:

| | RY | Ry | rY | ry |
|-------|------|------|------|------|
| **RY** | RRY Y | RRYy | RrYy | Rryy |
| **Ry** | RRYy | RRyy | RrYy | Rryy |
| **rY** | RrYy | RrYy | rrYy | rryy |
| **ry** | RrYy | Rryy | rrYy | rryy |

### Step 5: Count the Genotypes
From the Punnett square, we can count the different genotypes:
1. RRY Y (1)
2. RRYy (2)
3. RrYy (4)
4. Rryy (2)
5. RRyy (1)
6. RrYy (4)
7. rryy (1)

### Step 6: Write the Genotypic Ratio
Now, we can summarize the counts:
- 1 RRY Y
- 2 RRYy
- 4 RrYy
- 1 RRyy
- 2 Rryy
- 1 rryy

The genotypic ratio is:
- 1:2:2:1:4:1

### Final Genotypic Ratio
The final genotypic ratio for a dihybrid cross is **1:2:2:1:4:1**.

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