I am trying to distinguish between 393 and 374 band lengths by RFLP method. I am running in 3.5% agarose gel in 25x15cm gel electrophoresis to visualize the enzyme cut. I could not distinguish the bands with 60 minutes of running at 120 volts. When I ran for another 25 minutes, the bands faded, but the marker was visible. If I run it directly for 85 minutes, no bands including marker are visible in the gel. I also tried post staining method with ethidium bromide, but it didn't work. Any suggestions? Thank you...