Overview: Single nucleotide polymorphisms (SNPs) are DNA sequence variations that occur when a single nucleotide (A,T,C,or G) in the genome sequence is changed, which occur approximately once every 100 to 300 bases. There are many techniques for SNP detection and genotyping, such as restriction fragment length polymorphism PCR (RFLP-PCR), SSCP, allele specific hybridization, primer extension, allele specific oligonucleotide ligation, sequencing.