M. luteus can be found in many places such as the human skin, water, dust, and soil. Micrococcus is generally thought of as harmless bacterium, but there have been rare cases of Micrococcus infections in people with compromised immune systems, as occurs with HIV patients.
Therefore when used in gel electrophoresis, markers effectively provide a logarithmic scale by which to estimate the size of the other fragments (providing the fragment sizes of the marker are known). Protein, DNA, and RNA markers with pre-determined fragment sizes and concentrations are commercially available.
In summary, agarose gel electrophoresis is a method of separating biological molecules using an electrical current. Ethidium bromide is a molecule commonly used to visualize DNA in agarose gel electrophoresis experiments. It intercalates between the nitrogenous bases of DNA and fluoresces under UV light. Loading buffer is a solution added to an electrophoresis sample to give it color and density.