What is the criterion for DNA fragments movement on agarose gel during gel electrophoresis ?

Options

A. The large the fragmetn size , the farther it moves
B. The smaller the fragment size, the farther it moves
C. Positively charged fragments move to farther end
D. Negatively charged fragments do not move

Answer

### Step-by-Step Solution:

1. **Understanding Gel Electrophoresis**: Gel electrophoresis is a technique used to separate DNA fragments based on their size and charge. In this process, an agarose gel acts as a medium through which the DNA fragments move when an electric current is applied.

2. **Charge of DNA Fragments**: DNA molecules are inherently negatively charged due to the phosphate backbone. When an electric current is applied, these negatively charged DNA fragments will migrate towards the positively charged electrode (anode).

3. **Movement Based on Size**: The movement of DNA fragments through the agarose gel is also influenced by their size. Smaller DNA fragments can navigate through the pores of the gel more easily and therefore move faster compared to larger fragments, which encounter more resistance and move slower.

4. **Evaluating the Options**:
- **Option A**: "The larger the fragment size, further it moves" - This is incorrect because larger fragments move slower.
- **Option B**: "The smaller the fragment size, further it moves" - This is correct as smaller fragments can travel further in the gel.
- **Option C**: "Positively charged fragments move further and negatively charged fragments don't move" - This is incorrect because DNA is negatively charged and moves towards the positive electrode.
- **Option D**: "Negatively charged fragments don't move" - This is also incorrect since negatively charged DNA fragments do move towards the positive electrode.

5. **Conclusion**: The correct criterion for the movement of DNA fragments on agarose gel during gel electrophoresis is that smaller fragments move further than larger fragments due to their ability to pass through the gel matrix more easily.

### Final Answer:
The correct criterion for DNA fragments movement on agarose gel during gel electrophoresis is: **The smaller the fragment size, the further it moves.**