Final answer:
The Ames test measures if a chemical can cause DNA mutations, indicating mutagenic and potential carcinogenic properties. It uses mutated bacteria to assess the increase in mutation rate when exposed to the chemical, providing a fast and cost-effective screening tool compared to animal testing.
Step-by-step explanation:
The Ames test is a biological assay used to determine if a chemical is a mutagen. This test indicates whether a chemical has the potential to cause mutations in DNA, which can be a predictor for carcinogenicity. By employing a strain of Salmonella typhimurium that is unable to produce the amino acid histidine due to a genetic mutation, scientists can observe whether exposure to the chemical induces a mutation that restores the bacteria's ability to synthesize histidine. A positive Ames test indicates an increased number of such revertant colonies, which suggests that the chemical is mutagenic and may pose a cancer risk. This test is preferred over the use of animal models for initial screenings because it is more rapid, less expensive, and reduces the need for animal testing.