A cloning vector is a small piece of DNA that can be stably maintained in an organism, and into which a foreign DNA fragment can be inserted for cloning purposes. Describe the characteristics a cloning vector must possess. Why the DNA cannot pass through the cell membrane? Explain. How a bacterial cell is made 'competent to take up recombinant DNA from the medium?

Explanation

### Step-by-Step Solution:

1. **Definition of Cloning Vector**:
A cloning vector is a small piece of DNA that can be stably maintained in an organism, allowing for the insertion of a foreign DNA fragment for cloning purposes. This foreign DNA is often referred to as the "gene of interest".

2. **Characteristics of a Cloning Vector**:
- **Insertion Site**: A cloning vector must contain a site where the foreign DNA can be inserted. This is typically achieved using restriction enzymes that cut the DNA at specific sequences.
- **Selectable Markers**: The cloning vector should have selectable markers that help identify which cells have taken up the vector with the foreign DNA. This allows researchers to distinguish between transformants (cells that have taken up the vector) and non-transformants (cells that have not).
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