 In the first step, a genomic segment is amplified and attached to a bead through a PCR reaction with a biotinylated primer.In the second step, the amplified product is attached to a streptavidin column and washed with NaOH to remove the unbiotinylated strand.An allele-specific oligonucleotide is then added in the presence of a molecule that fluoresces when bound to double-stranded DNA.