The source nucleotide is represented along the rows. The destination nucleotide is represented along the columns. To interpret the measure at 1st passage G/10th passage A, one could say there is a 0.47% probability that a G in the first passage will become an A at the 10th passage, P(A in 10th passage ∣ G in 1st passage) = 0.47%. Transition frequencies have been highlighted in bold. Because the table contains conditional probabilities, i.e. not marginal probabilities, the percentages in each row will sum to 100%, but the percentages down each column may not.