point mutation has transition (when a purine base is substituted with another purine or pyramidine with pyramidine) or transversion (purine with pyramidine or vice versa) point mutations give rise to silent mutation, nonsense mutation and missense mutation. silent mutations are the least harmful cause their change of the base does not result in anything cause they code for the same amino acid. missense codes for a different amino acid, and nonsense codes for a stop codon.