A method for determining the presence of an allele, including (a) binding a polymerase to a double stranded nucleic acid that includes a primer hybridized to a template, the template including a first allele of a locus; (b) adding a nucleotide to the primer via catalytic activity of the polymerase, thereby producing an extended nucleic acid; (c) dissociating the polymerase from the extended nucleic acid; (d) detecting dissociation of the polymerase from the extended nucleic acid; and (e) comparing the dissociation of the polymerase from the extended nucleic acid to dissociation of the polymerase from a second double stranded nucleic acid, the second double stranded nucleic acid including a primer hybridized to the same position of the locus as the primer of the extended nucleic acid.