| | Re: Why should TM be same for Primers?
The thermodynamics of a successful PCR reaction is based on the Temperature of annealing (Tm) of your primers at the appropriate sites in your template so as to produce the desired amplicon. This determines the strength of binding of your primers to the desired site. Lowering of the Tm usually causes misamplification leading to spurious products along with your desired product. Hence, Tm also maintains stringency of the reaction. The reaction mixture is held at various temperature steps in the cycle including denaturation, annealing and extension, among which the annealing temperature should be ideally a temperature that would allow the primers to bind to the desired regions, and only a single temperature can be maintained. Hence that single temperature of annealing would maintain stringency of binding for both primers only if they both share the same or around the same Tm.
There, hope this was useful!