Gel electrophoresis is used for

Options

A. (a) construction of recombinant DNA using cloning vectors
B. (b) isolation of DNA molecules
C. (c) cutting of DNA into fragments
D. (d) separation of DNA fragments according to their size.

Answer

**Step-by-step Solution:**

1. **Understanding Gel Electrophoresis**: Gel electrophoresis is a technique used to separate macromolecules, primarily nucleic acids (DNA or RNA) and proteins, based on their size and charge.

2. **Principle of Gel Electrophoresis**: The process relies on the fact that DNA molecules are negatively charged due to their phosphate backbone. When an electric current is applied, these negatively charged molecules will migrate towards the positive electrode.

3. **Setup of the Gel**: In a typical setup, an agarose gel is prepared with wells where the DNA samples are loaded. The gel acts as a medium through which the DNA fragments can move.

4. **Migration of DNA Fragments**: As the electric current is applied, smaller DNA fragments move faster and travel further through the gel compared to larger fragments, which move more slowly. This results in the separation of DNA fragments based on size.

5. **Interpreting Results**: After the electrophoresis run is complete, the gel is stained to visualize the DNA bands. The bands represent different sizes of DNA fragments, with the position of each band indicating its size relative to others.

6. **Conclusion**: Based on the principle and results of gel electrophoresis, the correct answer to the question is that gel electrophoresis is used for the separation of DNA fragments according to their size.

**Final Answer**: D. Separation of DNA fragments according to their size.

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