What is the first step in the Southern Blot technique

Options

A. Denaturation of DNA on the gel for hybridization with specific probe
B. Production of a group of genetically identical cells
C. Digestion of DNA by restriction enzyme
D. Isolation of DNA from a nucleated cell such as the one from the scene of crime.

Explanation

### Step-by-Step Solution:

1. **Understanding Southern Blot Technique**: The Southern Blot technique is a method used to detect specific DNA sequences within a DNA sample. It involves several steps to isolate, fragment, and analyze DNA.

2. **Identifying the First Step**: The first step in the Southern Blot technique is the isolation of DNA from a nucleated cell. This could be from various sources, including a sample from a crime scene.

3. **Fragmentation of DNA**: After isolation, the next step involves breaking the DNA into smaller fragments. This is typically done using restriction enzymes that cut the DNA at specific sequences.

4. **Gel Electrophoresis**: The fragmented DNA is then separated according to size using gel electrophoresis. This process allows for the visualization of the DNA fragments based on their length.

5. **Denaturation of DNA**: Following separation, the double-stranded DNA fragments are denatured, meaning they are separated into single strands. This is crucial for the subsequent hybridization step.

6. **Transfer to Blotting Membrane**: Finally, the single-stranded DNA is transferred from the gel to a blotting membrane, where it can be probed for specific sequences.

### Conclusion:
The first step in the Southern Blot technique is the **isolation of DNA from a nucleated cell**.