<p>In this simulation, colored beads were poured through each set of clear tubes.  The beads represented chemicals or molecules entering a pathway which would alter them.  The tubes represented the pathways which consisted of different genes being expressed at different levels.  The first scenario represents a properly engineered pathway where the output of both genes is similar.  This model allowed the beads to flow through the tubes with a constant pace.  Our second scenario represented what can happen when a gene in the pathway is over-expressed.  Here, the first gene was expressing at almost double what the second gene could take in.  This caused the beads to build-up in the first tube while only allowing a small amount through the rest of the pathway.</p>