In recombinant DNA technology before the use of restriction endonuclease , we have to isolated and precipitate the genetic material (DNA) . For this purpose we use following different enzyme / chemical :

Options

A. Ethidium bromide
B. RNA polymerase
C. `T_4` ligase
D. Chilled Ethanol

Answer

To solve the question regarding the enzymes or chemicals used to isolate and precipitate DNA before the use of restriction endonucleases in recombinant DNA technology, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for the enzymes or chemicals used to isolate and precipitate DNA prior to the application of restriction endonucleases in recombinant DNA technology.

2. **Evaluating the Options**:
- **Option 1: Ethidium Bromide**: This is an intercalating agent used primarily for staining DNA in gel electrophoresis. It does not play a role in isolating or precipitating DNA. **(Incorrect)**
- **Option 2: RNA Polymerase**: This enzyme synthesizes RNA from a DNA template and is not involved in the isolation or precipitation of DNA. **(Incorrect)**
- **Option 3: T4 Ligase**: This enzyme is used to join DNA fragments together but is not used for isolating or precipitating DNA. **(Incorrect)**
- **Option 4: Chilled Ethanol**: Chilled ethanol is commonly used to precipitate DNA from a solution. When DNA is mixed with chilled ethanol, it becomes less soluble and precipitates out of the solution. **(Correct)**

3. **Conclusion**: After evaluating all the options, the correct answer is **Option 4: Chilled Ethanol**.