 if it is always possible to go from a state formula_23 to a state formula_24 (possibly in several steps), then it is also ergodic.As a result, it has a unique "stationary distribution" formula_50, where formula_51 corresponds to the proportion of time spent in state formula_23 after the Markov chain has run for an infinite amount of time.In DNA evolution, under the assumption of a common process for each site, the stationary frequencies formula_53 correspond to equilibrium base compositions.