What factor primarily influences the resolution of DNA fragments on an agarose gel?

What factor primarily influences the resolution of DNA fragments on an agarose gel?

• A. The buffer used for electrophoresis
• B. The concentration of agarose in the gel
• C. The DNA sequence
• D. The staining method

Answer: (B)

The key idea is that the gel’s pore size, set by how much agarose you mix into the gel, determines how DNA fragments of different lengths move and separate. Higher agarose concentration creates smaller pores, which makes it easier to distinguish fragments that are close in size—especially smaller fragments—but it also slows their overall movement. Conversely, a lower concentration has larger pores, allowing fragments to migrate more quickly but with less ability to resolve near-sized fragments. This is why the factor primarily shaping resolution is the agarose concentration: it directly controls how finely the gel can discriminate between DNA fragment lengths. Other choices—the buffer, the DNA sequence, or the staining method—mainly affect stability, visualization, or general migration speed, not how well similar-sized fragments are separated.

The key idea is that the gel’s pore size, set by how much agarose you mix into the gel, determines how DNA fragments of different lengths move and separate. Higher agarose concentration creates smaller pores, which makes it easier to distinguish fragments that are close in size—especially smaller fragments—but it also slows their overall movement. Conversely, a lower concentration has larger pores, allowing fragments to migrate more quickly but with less ability to resolve near-sized fragments.

This is why the factor primarily shaping resolution is the agarose concentration: it directly controls how finely the gel can discriminate between DNA fragment lengths. Other choices—the buffer, the DNA sequence, or the staining method—mainly affect stability, visualization, or general migration speed, not how well similar-sized fragments are separated.