A high affinity, triplex-forming oligonucleotide and methods for use thereof wherein an oligonucleotide is used to form a triple-stranded nucleic acid molecule with a specific DNA segment of a target DNA molecule. Upon formation of the triplex, the binding of the oligonucleotide stimulates mutagenesis within or adjacent to the target sequence using cellular DNA synthesis or repair mechanisms thereby producing heritable changes in a human or animal. The mutation activates, inactivates or alters the activity and function of the target molecule. This mutation may be the result of a recombinagenic mechanism induced by the oligonucleotide.