Originally Posted by butters
@wishmaes, can u show us the gel?
DNA migration is from black to red. etbr is from red to black thus longer u ran the gel the less etbr will be at red part of the tank. That is the part where ur low molecular weight DNA will be at the end of the run. It occured when u ran a pre-stain gel. the easiest way is to look at ur ladder. does the 100bp or 200bp is faint and almost disappear? However if the ladder band for 100bp or 200bp is very strong thus it is not related to etbr or running too long. so if possible show us the gel with the ladder beside the pcr product and tell us how much u load. thank!
I will agree with you totally. Prolonged run of a gel, means that you EtBr will migrate off your gel, and QQ then for your bands. In that case you might be able to restain your gel with EtBr, though is not recommended. Also check the intensity of your UV lamps. It has been reported that prolonged exposure of a DNA gel under a strong UV lamp may diffuse and ultimately disappear your DNA bands.