**7.6 Touchdown PCR (step-down PCR)**

This type of PCR is designed to minimize nonspecific amplification by gradually decreasing the primer annealing temperature in the successive cycles. PCR is started with initial cycles having an annealing temperature 3–5°C higher than the primer Tm. The annealing temperature is then gradually decreased to 3–5°C lower below the Tm. The higher annealing temperature increases the specificity of the primers at initial stages of the reaction, while the lower temperature permits more efficient amplification later at the end [4, 7, 46].
