Figure 2.

Effect of T_m constraints and sequence database size on size of universal primer set. The number of primers in the universal set for all viruses is shown, as a function of primer size. Calculations were based either on sequence data available April 2007 and imposing T_m constraints in primer selection, or without T_m or GC% constraints, or based on January 2004 sequence data with T_m constraints. For primer size of 5 with T_m constraints, a constraint of T_m > 0 was used, delivering primers with GC% of 80–100%.