Viruses are small. So small that you cannot see them, even with standard microscopes. Have you ever wondered how researchers work with and quantitate viruses without being able to see them? Depending on the virus and the type of cell it infects, several different approaches can be employed. When grown in liquid culture, infected host cells will be killed and sometimes this can be easily seen. For example, photosynthetic algae are green when grown in culture, but lose this color when they are killed, making it easy to visualize when an infection has killed the algal cells. For other viruses, like poliovirus, infected cells adhere to the surface of a plate and as the virus kills those cells, empty areas start to appear. These areas, called plaques, can be more easily seen by staining the cells and counting the clear plaques that appear. A related technique is used for other viruses, like retroviruses, where host cells are genetically altered so that when a virus infects that cell and begins expressing its genes, it will also activate the expression of a biomarker that turns blue when stained. This approach is faster because it does not require the virus to complete several rounds of replication to kill the host cells and create a plaque. Instead, the infected cells will appear blue and can be directly counted. Students in Virology 3150 will be learning these important techniques to study both mammalian and algal viruses in Spring quarter.