The addition of DNA Loading Buffer to a DNA sample adds color and increases the density to simplify the loading process. It contains two dyes, bromphenol blue and xylene cyanol FF, at low concentrations to avoid masking DNA fragments in the samples. In an electric field, the dyes move toward the anode at predictable rates. After electrophoresis, the buffer yields two clearly separated bands of color: in agarose gels from 0.5% to 1.4% in concentration, bromphenol blue migrates with 300bp linear double-stranded DNA fragment, whereas xylene cyanol FF co-migrates with linear double-stranded DNA approximately 4kb length.