A virus is found to exist in N different strains and in each generation either stays the same or mutates into another strain with probability p/(N 1). Show that the probability that the strain in the n-th generation is the same as that at time zero is 1 pN + + (1 - 7) ( - 27) " N N-1 [Hint: Model this as a 2-state Markov process with the two states being "initial strain" and "other strain".]