2.Molecular Evidence - use molecular techniques to determine differences in genes between normal and cancer tissues. These mutations may lead to differences in cell phenotype in vitro. Example - when rats were treated with nitrosomethylurea, a DNA alkylating agent, theydeveloped beast tumors that contained mutated ras oncogenes. Can also scan precancerous cells for abnormalities such as increases in chromosome number, loss of dependence on growth factors, and immortalized growth. Ames Test - Assays the mutagenicity of chemicals in special mutated strains of Salmonella bacteria.
Some strains detect nucleic acid substitution while another detects frame-shift mutations.
The complete battery tests 4 mutatnt strains of bacteria, each detecting a different kind of mutation. These bacteria are mutants that are unable to produce histidine needed for their growth. Test to see whether a chemical reverts the bacteria to the wild-type strain that can grow without added histidine. Mammalian cell culture are also performed using cells deficient in HPRT which can't synthesize nucleic acids. Normal cells die in the prescnce of these drugs while mutated cells can grow.