Abstract: The invention pertains to a method for targeted alteration of a duplex acceptor DNA sequence, comprising combining the duplex acceptor DNA sequence with a donor oligonucleotide, wherein the duplex acceptor DNA sequence contains a first DNA sequence and a second DNA sequence which is the complement of the first DNA sequence and wherein the donor oligonucleotide comprises a domain that comprises at least one mismatch with respect to the duplex acceptor DNA sequence to be altered, preferably with respect to the first DNA sequence, and wherein a section of the donor oligonucleotide is methylated to a higher degree than the second DNA sequence and/or wherein the second DNA is methylated to a lower degree than the corresponding section of the donor oligonucleotide, optionally in the presence of proteins that are capable of targeted nucleotide exchange and to oligonucleotides for use in the method.