The Ames Test: Videos & Practice Problems

The Ames test is a scientific screening experiment designed to determine if a chemical is a mutagen, which means it can induce mutations in DNA. The test involves using control and experimental plates with His- bacteria on minimal media that lacks histidine. If the test chemical is a mutagen, it will induce mutations that convert His- bacteria to His+ bacteria, resulting in many His+ colonies. Conversely, if few colonies form, the chemical is not a mutagen. The number of His+ colonies directly correlates with the mutagenicity of the chemical, meaning more colonies indicate a higher mutagenic potential.

The Ames test determines if a chemical is a mutagen by observing the growth of His+ colonies on minimal media plates that lack histidine. His- bacteria are added to both control and experimental plates. The control plate receives a non-mutagenic chemical, while the experimental plate receives the test chemical. If the test chemical is a mutagen, it will induce mutations that convert His- bacteria to His+ bacteria, resulting in many His+ colonies. If the number of His+ colonies on the experimental plate is significantly higher than on the control plate, the chemical is considered a mutagen.

In the Ames test, histidine plays a crucial role in determining whether a chemical is a mutagen. The test uses minimal media that lacks histidine, meaning only His+ bacteria can grow on it. His- bacteria, which require histidine to grow, are added to the plates. If a test chemical induces mutations that convert His- bacteria to His+ bacteria, these His+ bacteria will grow and form colonies. The presence of many His+ colonies indicates that the test chemical is a mutagen, while few colonies suggest it is not.

In the Ames test, the control group consists of a plate with His- bacteria and a non-mutagenic chemical. This plate serves as a baseline to account for spontaneous mutations that naturally occur, resulting in a few His+ colonies. The experimental group consists of a plate with His- bacteria and the test chemical. If the test chemical is a mutagen, it will induce mutations that convert His- bacteria to His+ bacteria, resulting in many His+ colonies. Comparing the number of His+ colonies between the control and experimental groups helps determine the mutagenicity of the test chemical.

A high number of His+ colonies in the Ames test indicates that the test chemical is a mutagen. The test involves adding His- bacteria to minimal media plates that lack histidine. If the test chemical induces mutations that convert His- bacteria to His+ bacteria, these His+ bacteria will grow and form colonies. A high number of His+ colonies suggests that the chemical has a high mutagenic potential, as it has induced a significant number of mutations. Conversely, few His+ colonies indicate that the chemical is not a mutagen.