In this lab, we will demonstrate the concept of natural selection. We will start with a population of color-coded bacteria (white and purple). The white bacteria represents a mutant with a growth advantage. The students will watch as the relative frequency of the white bacteria increases with time. Eventually, the white bacteria will completely overtake the population, a phenomenon known as an adaptive sweep.
An introduction to the lab can be found here.
Natural Selection describes serial dilution and has the worksheet for students. They will calculate growth of the bacteria, and the selection coefficient s for the white/purple strains.