Certified in Public Health (CPH) Practice Exam

Which assay is best for detecting genetic damage from ionizing radiation exposure?

1. Comet (or single-cell gel electrophoresis) assay

2. Ames test for reversion mutations

3. Increased mutation frequency at the HGPRT locus of hamster cells

4. None of these assays

The correct answer is: Comet (or single-cell gel electrophoresis) assay

The Comet assay, also known as single-cell gel electrophoresis, is highly effective for detecting genetic damage caused by ionizing radiation. This assay allows for the quantification of DNA strand breaks in individual cells. When cells are exposed to ionizing radiation, the DNA can become fragmented. The Comet assay involves embedding cells in a gel and subjecting them to an electric field, which causes the fragmented DNA to migrate out of the cell like a comet tail—hence the name. The extent of DNA damage can then be quantified by measuring the tail length and intensity, providing a clear indicator of genetic damage. In contrast, the other assays mentioned focus on different mechanisms of mutagenesis or do not specifically target the type of damage caused by radiation. For instance, the Ames test is utilized primarily to assess the mutagenic potential of compounds through the reversion of mutations in bacteria, while the increased mutation frequency at the HGPRT locus is more related to assessing overall mutation rates rather than directly measuring DNA damage from radiation exposure. Therefore, the Comet assay is the most appropriate choice for detecting specific genetic damage resulting from ionizing radiation exposure.