FAQ: Why are the some of the bands in the DNA Ladder fainter at the bottom of the gel?

Most gel stains run in the opposite direction from that of the migrating DNA. As a result, the bottom of the precast gel might have a lower concentration of stain, which might result in un-uniform staining of the bottom bands. How much of the gel will end up with a lower stain concentration is highly dependent on the migration conditions (gel percentage, voltage, buffer, run time, etc.). This effect can be counteracted by adding some gel stain to the running buffer.