 In this experiment, as in most molecular biology techniques, a control must be used to ensure successful experimentation.In molecular biology, procedures and technologies are continually being developed and older technologies abandoned.For example, before the advent of DNA gel electrophoresis (agarose or polyacrylamide), the size of DNA molecules was typically determined by rate sedimentation in sucrose gradients, a slow and labor-intensive technique requiring expensive instrumentation; prior to sucrose gradients, viscometry was used.