 As a result, if a given allele is present in the PCR reaction, the primer pair specific to that allele will produce product but not to the alternative allele with a different SNP.The two primer pairs are also designed such that their PCR products are of a significantly different length allowing for easily distinguishable bands by gel electrophoresis or melt temperature analysis.In examining the results, if a genomic sample is homozygous, then the PCR products that result will be from the primer that matches the SNP location and the outer opposite-strand primer, as well from the two outer primers.