Abstract: Methods and compositions are provided for detecting DNA sequences, particularly single nucleotide polymorphisms, using a pair of nucleotide sequences, a primer and a snp detection sequence, where the snp detection sequence binds downstream from the primer to the target DNA in the direction of primer extension. The snp detection sequence is characterized by having a nucleotide complementary to the snp and adjacent nucleotides complementary to adjacent nucleotides in the target and an electrophoretic tag bonded to the 5′-nucleotide. The pair of sequences is combined with the target DNA under primer extension conditions, where the polymerase has 5′-3′ exonuclease activity. When the snp is present, the electrophoretic tag is released and can be detected by electrophoresis as indicative of the presence of the snp in the target DNA. The sequence containing the snp is exemplary of DNA sequences of interest generally.