In a dihybrid test cross the genotypic ratio of the progeny is

Options

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

Explanation

To solve the question regarding the genotypic ratio of progeny in a dihybrid test cross, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Dihybrid Cross**:
- In a dihybrid cross, we consider two traits. For example, let's take seed shape (round vs. wrinkled) and seed color (yellow vs. green).
- Round (R) is dominant over wrinkled (r), and yellow (Y) is dominant over green (y).

2. **Identify the Parent Genotypes**:
- For the first parent (dihybrid), we can assume the genotype is RrYy (round yellow).
- The second parent (double recessive) will have the genotype rryy (wrinkled green).

3. **Determine the Gametes**:
- The first parent (RrYy) can produce four types of gametes due to independent assortment:
- RY (Round Yellow)
- Ry (Round Green)
- rY (Wrinkled Yellow)
- ry (Wrinkled Green)
- The second parent (rryy) can only produce one type of gamete:
- ry (Wrinkled Green)

4. **Set Up the Punnett Square**:
- We can set up a Punnett square to visualize the combinations of gametes:
```
| ry
------------
RY | RrYy (Round Yellow)
Ry | Rryy (Round Green)
rY | rrYy (Wrinkled Yellow)
ry | rryy (Wrinkled Green)
```

5. **Analyze the Progeny Genotypes**:
- From the combinations, we can see the resulting genotypes of the progeny:
- RrYy (Round Yellow)
- Rryy (Round Green)
- rrYy (Wrinkled Yellow)
- rryy (Wrinkled Green)

6. **Determine the Genotypic Ratio**:
- The resulting genotypes are in the ratio of 1:1:1:1.
- Therefore, the genotypic ratio of the progeny in a dihybrid test cross is 1:1:1:1.

### Conclusion:
The genotypic ratio of the progeny in a dihybrid test cross is **1:1:1:1**.