The micronucleus test is widely employed in environmental health research. It can also be an excellent tool for learning important concepts in environmental health. In this article we present an inquiry-based laboratory exercise where students explore several theoretical and practical aspects of environmental mutagenesis employing the micronucleus as a central landmark. Performing the test in mussels exposed to colchicine and comparing the results with a control group, they learn (or refresh previous concepts) about cytogenetics and chromosome segregation in cell divisions; about DNA molecular structure and how it can be altered by different agents (mutagenesis); and about the value of basic genetic processes for applied research, for example biomarkers. (Contains 1 figure and 1 table.)