The number of type of genomes found in recombinant cosmids is ( when only 1 gene is introduced)

Options

A. 1
B. 3
C. 2
D. Many

Answer

To determine the number of types of genomes found in recombinant cosmids when only one gene is introduced, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Cosmids**: Cosmids are hybrid vectors that combine features of plasmids and bacteriophage lambda. They are used in cloning and can carry larger DNA fragments than traditional plasmids.

2. **Identify Components of Cosmids**: Cosmids consist of:
- **Plasmid DNA**: This is the circular DNA that can replicate independently within a bacterial cell.
- **Cos Sites**: These are sequences derived from the lambda phage that allow the cosmid to be packaged into a phage particle.

3. **Determine Existing Genomes in Cosmids**: A normal cosmid already contains two types of genomes:
- The genome of the plasmid.
- The genome from the lambda phage (cos sites).

4. **Introduce a New Gene**: When we introduce one gene from an external organism into the cosmid, we are essentially adding a third type of genome. This gene will be integrated into the existing cosmid structure.

5. **Count the Total Types of Genomes**:
- Existing genomes: 2 (from the plasmid and lambda phage).
- New genome introduced: 1 (the gene from the external organism).
- Total: 2 (existing) + 1 (new) = 3 types of genomes.

### Final Answer:
The total number of types of genomes found in recombinant cosmids when only one gene is introduced is **3**.

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