Gel electrophoresis is used for

Options

A. construction of recombinant DNA by joining with cloning vectors
B. isolation of DNA molecule
C. cutting of DNA into fragments
D. separation of DNA fragments according to their size

Answer

**Step-by-Step Solution:**

1. **Understanding Gel Electrophoresis**: Gel electrophoresis is a technique used in molecular biology to separate macromolecules like DNA, RNA, or proteins based on their size.

2. **Principle of Gel Electrophoresis**: The process involves placing DNA fragments in a gel matrix and applying an electric current. Since DNA is negatively charged due to its phosphate backbone, it will migrate towards the positive electrode when the current is applied.

3. **Movement of DNA Fragments**: The rate at which DNA fragments move through the gel depends on their size. Smaller fragments move faster and travel further through the gel compared to larger fragments, which move more slowly.

4. **Analyzing the Options**:
- **Option A**: Construction of recombinant DNA by joining with cloning vectors - This is incorrect as gel electrophoresis does not involve joining DNA fragments.
- **Option B**: Isolation of DNA molecules - This is also incorrect; gel electrophoresis does not isolate DNA but separates fragments.
- **Option C**: Cutting of DNA into fragments - This is incorrect; gel electrophoresis does not cut DNA but separates already cut fragments.
- **Option D**: Separation of DNA fragments according to their size - This is correct as gel electrophoresis is specifically designed for this purpose.

5. **Conclusion**: The correct answer is that gel electrophoresis is used for the separation of DNA fragments according to their size.

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