The present invention provides novel donor polynucleotides formed by linking the two ends of a genomic fragment containing a cleavable site by a polynucleotide carrying a positive selection marker gene and a negative selection marker gene. Use of the donor polynucleotide makes it possible to modify only a target gene with avoiding the possibility of introducing mutations to sequences, called off-target, which are other than the target sequence, by introducing cleavage in a homologous site of the donor polynucleotide without introducing cleavage in a target gene locus.

The present invention provides donor polynucleotides formed by linking the two ends of a genomic fragment containing a cleavable site by a polynucleotide carrying a positive selection marker gene and a negative selection marker gene. Use of the donor polynucleotide makes it possible to modify only a target gene with avoiding the possibility of introducing mutations to sequences, called off-target, which are other than the target sequence, by introducing cleavage in a homologous site of the donor polynucleotide without introducing cleavage in a target gene locus.