Abstract: A method of genotyping single nucleotide polymorphisms (SNP) and point mutations in nucleic acid based on chain extension by polymerase. This invention is based on the fact that the nucleoside immediately 5′ adjacent to any SNP/point mutation site is known, and the neighboring sequence immediately 3′ adjacent to the site is also known. A primer complimentary to the sequence directly adjacent the 3′ side of the SNP in a target polynucleotide is used for chain elongation. The polymerase reaction mixture contains one chain terminating nucleotide having the base complimentary to nucleotide directly adjacent to the 5′ side of the SNP of the target polynucleotide. An additional dNTP may be added to produce a primer with the maximum of two base extension. The resultant elongation/termination reaction product are analysed for incorporation of the chain terminator nucleotide or for chain length extension of the primer.