Primer weight score calculation. (A) SPEC mode: The first 15 nucleotides starting from the 3' end are used for the calculation. A value of 214 is assigned to the first nucleotide, 213 to the second and so on if that nucleotide is a SNP. Primer weight score is the sum of all the values assigned to SNPs. (B) COMN mode: primer weight is the difference between the optimum amplicon size and the actual amplicon size (default = 600 bp).