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.
The idea behind DNA gel electrophoresis is to separate the fragments of a DNA sample and compare the results to a positive and negative control to determine if a DNA sample contains a particular gene. The size of the DNA fragments in the sample are determined by the specific primers used to fragment the DNA.