State the null hypothesis for the experiment whose data are graphed in Figure 2. Provide evidence to support or refute the scientists’ claim that more colonies grew in strains C3 and C6 than in the other strains because the genes for proteins that are normally targeted by the toxic chemical contain nucleotides with incorrect bases in the C3 and C6 cells. The scientists additionally determined that the C3 and C6 strains had no decrease in virulence (disease-causing ability) in comparison with the virulence of the other clinical isolate strains and concluded that these two strains have mutator phenotypes. Explain why mutator phenotypes were found only among clinical isolate strains and not among environmental strains.