In the Markov process, five categories of transition events change the state of the system. The rates of all of these events are denoted by φi. Processes 2, 3, and 5 all result from phages infecting the bacteria. Processes 4 results from phage infecting some bacteria, which could be the population under study, or a different host population of bacteria. There is an additional category of events, not shown in this figure, which is evolution of the virus due to mutation or recombination.