The function of loading dye in electrophoresis is to allow the DNA sample to sink into the wells of the gel and to allow scientists to visually track the DNA sample as it runs through the gel. Gel electrophoresis is a method used by scientists to separate DNA into various size strands. The loading dye causes the DNA sample to be denser than the running buffer.
The difference in density forces the DNA sample to sink into the bottom of the well and prevents the sample from diffusing into the buffer. Loading dyes consist of tracking dyes that migrate with the DNA samples. Glycerol and bromophenol blue is a common mixture used to create a loading buffer. The glycerol binds to the DNA and makes it heavier, while bromophenol blue stains the DNA. An ethidium bromide solution is generally used when running a gel electrophoresis. Ethidium bromide is a chemical that can be seen under ultraviolet lighting. Ethidium bromide and other fluorescent dyes bind to DNA samples and glow when placed in a transilluminator. The amount of dye used is crucial when running a gel electrophoresis. Specific dyes correlate to certain band sizes in DNA samples. Too much or too little dye can obscure the expected DNA sample size.