In   the   next   round   of
   replication,  the  mismatched  members  of the base pair separate; the
   tautomer usually shifts back to its normal isomer.

   Replication of the 2 strands by normal base pairing results in a point
   mutation  called a transition mutation, where a purine substitutes for
   a purine, or a pyrimidine substitutes for a pyrimidine.

   In this example, the wild type T - A pair has mutated to C - G.