Which one of the following is used as vector for cloning genes into higher organisms ?

Options

A. Baculovirus
B. Salmonella typhimurium
C. Rhizopus nigricans
D. Retrovirus

Answer

To determine which vector is used for cloning genes into higher organisms, let's analyze the options provided:

1. **Baculovirus**: This is a virus commonly used as a vector for gene expression in insect cells. While it is effective for insect systems, it is not typically used for higher organisms like mammals.

2. **Salmonella typhimurium**: This bacterium is known for its plasmids and is primarily used in bacterial transformation studies. It has applications in vaccine development but is not a common vector for cloning genes into higher organisms.

3. **Rhizopus negricans**: This is a multicellular fungus. While fungi can be used in genetic studies, they are not the primary vectors for cloning genes into higher organisms.

4. **Retrovirus**: Retroviruses are RNA viruses that can integrate their genetic material into the host's DNA. They are widely used as vectors for gene therapy and for cloning genes into higher organisms, especially in mammalian cells. The reverse transcriptase enzyme allows the conversion of RNA into DNA, which can then be integrated into the host genome.

Based on this analysis, the correct answer is **Retrovirus**.

### Step-by-Step Solution:
1. **Identify the options**: Baculovirus, Salmonella typhimurium, Rhizopus negricans, Retrovirus.
2. **Analyze each option**:
- Baculovirus: Used in insect cells, not higher organisms.
- Salmonella typhimurium: Used in bacterial transformation, not primarily for higher organisms.
- Rhizopus negricans: A fungus, not typically used for cloning in higher organisms.
- Retrovirus: RNA virus that integrates into host DNA, suitable for higher organisms.
3. **Determine the most suitable vector**: Retrovirus is the most appropriate choice for cloning genes into higher organisms.