Gel electrophoresis is used for

Options

A. Isolation of DNA molecule
B. Cutting of DNA into fragments
C. Separation of DNA fragments according to their size
D. Construction of recombinant DNA by joining with cloning vectors

Answer

### Step-by-Step Solution:

1. **Understanding Gel Electrophoresis**: Gel electrophoresis is a laboratory technique used to separate mixtures of DNA, RNA, or proteins based on their size and charge.

2. **Identifying the Charge of DNA**: DNA molecules are negatively charged due to the phosphate backbone. This property is crucial for the electrophoresis process.

3. **Setting Up the Gel**: In gel electrophoresis, a gel matrix (usually agarose or polyacrylamide) is prepared and placed in a chamber. The gel acts as a medium through which the DNA fragments will move.

4. **Applying Electric Current**: An electric current is applied across the gel. The negative end (cathode) is connected to the side where the DNA samples are loaded, and the positive end (anode) is on the opposite side.

5. **Movement of DNA Fragments**: Since DNA is negatively charged, it will migrate towards the positive electrode. Smaller DNA fragments move faster and travel further through the gel than larger fragments.

6. **Separation Based on Size**: As the electric current runs, the DNA fragments are separated based on their size. Smaller fragments will be found further away from the starting point compared to larger fragments.

7. **Conclusion**: The primary purpose of gel electrophoresis is to separate DNA fragments according to their size. Therefore, the correct answer to the question is that gel electrophoresis is used for the separation of DNA fragments according to their size.

### Final Answer:
Gel electrophoresis is used for the separation of DNA fragments according to their size.

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