Screening methods. Schematic illustration of different ways to screen away a dominating DNA template in a PCR mixture. 1. Universal primers amplifying target and non-target DNA and removal of non-target DNA prior or after PCR with restriction enzymes. 2. Species-specific PCR primers amplifying only target-DNA. 3. Group-specific PCR primers amplifying groups excluding non-target sequence. 4. Blocking non-target amplification, only target sequences amplified using universal PCR primers a) annealing inhibiting blocking primer, b) elongation arrest blocking primer c) annealing inhibiting DPO blocking primer.