Abstract: In order to facilitate the screening of an organism, or a population of organisms, carrying heterozygous mutations for identifying the presence of a mutation in a gene of interest, a method is provided which utilizes mismatch binding proteins, such as MutS. The method comprises the steps of denaturing double stranded nucleic acid present in a nucleic acid sample from an organism; allowing the nucleic acid to anneal; and removing homoduplexes from the annealed sample, thereby retaining heteroduplexes in the sample. A positive signal from a probe specific for the gene of interest indicates that the organism carries a mutation in the gene.