The genotypes of a plant variety were TtHh, Tthh, ttHh and tthh, where T = tallness and H= hairy stem. Which one of the following crosses would produce progeny giving a phenotypic ratio approximately 1:1:1:1 ?

Options

A. `TtHhxx TtHh`
B. `TtHhxxTthh`
C. `TtHhxxttHh`
D. `TtHhxxtthh`

Answer

To solve the problem, we need to determine which cross among the given options would yield a phenotypic ratio of approximately 1:1:1:1 for the traits of tallness (T) and hairy stem (H) in plants.

### Step-by-Step Solution:

1. **Identify the Genotypes**: The genotypes provided are:
- TtHh (tall and hairy)
- Tthh (tall and smooth)
- ttHh (short and hairy)
- tthh (short and smooth)

Here, T (tall) and H (hairy) are dominant traits, while t (short) and h (smooth) are recessive traits.

2. **Understanding the Desired Ratio**: A phenotypic ratio of 1:1:1:1 means that we want to produce four different phenotypes in equal proportions. This typically occurs when we cross a heterozygous individual with a homozygous recessive individual.

3. **Select the Appropriate Cross**:
- To achieve a 1:1:1:1 ratio, we can cross a heterozygous individual (TtHh) with a homozygous recessive individual (tthh). This cross will produce gametes from both parents that can combine in such a way to yield four distinct phenotypes.

4. **Using a Punnett Square**:
- For the cross TtHh (heterozygous) x tthh (homozygous recessive):
- The gametes from TtHh are: TH, Th, tH, th
- The gametes from tthh are: th (only one type)
- Filling in the Punnett square:
```
th
----------------
| TtHh | tall and hairy
| Tthh | tall and smooth
| ttHh | short and hairy
| tthh | short and smooth
```
- The resulting phenotypes will be:
- Tall and hairy (TtHh) - 1
- Tall and smooth (Tthh) - 1
- Short and hairy (ttHh) - 1
- Short and smooth (tthh) - 1

5. **Conclusion**: The cross TtHh x tthh yields a phenotypic ratio of 1:1:1:1, confirming that this is the correct cross to achieve the desired outcome.

### Final Answer:
The cross that would produce progeny giving a phenotypic ratio approximately 1:1:1:1 is **TtHh x tthh** (Option D).