Teams of computer scientists and biology students work together to develop a simulated experiment on mutations in mice. The simulation is programmed with the complete sequence of mouse DNA. Then it calculates the frequency of mutations under three conditions: when the mice are subjected to tobacco smoke, subjected to ultraviolet radiation, and kept under normal conditions. For each mutation, the simulation identifies whether the mutation affects a mouse protein. The biology students prepare the data table shown below to organize the results of the simulation. Conditions Frequency of Mutations (altered DNA base pairs) Percent of Mutations that Affect Proteins Normal Tobaco Smoke Ultraviolet Light What is the independent variable of the simulated experiment?