The 6X gel loading buffer is composed of 0.03% Bromophenol Blue, 0.03% Xylene cyanol FF, 60 mM EDTA, pH 7.6 and 60% glycerol calcium or magnesium in molecular biology grade water. The EDTA is added as a chelating agent to terminate enzymatic reactions requiring magnesium. Adding 1 volume of DNA Gel Loading Buffer to 9 or 5 volumes of sample increases the density of the sample and gives it color, thus facilitating loading. In addition, the two dyes migrate in the same direction as nucleic acids, serving as rough indicators of the electrophoretic progress.