This unit provides a set of protocols for high throughput SNP genotyping using oligonucleotide microarrays. The basic protocol utilizes allele-specific hybridization in which the microarray provides both the allele discrimination and read-out. In the alternate approach, the allele discrimination is accomplished in solution and then the array is used to provide the read-out of the genotyping reaction. Single nucleotide polymorphisms (SNPs) offer several advantages over other genetic markers including their high density in the.