“…Listed below are the most commonly applied external standards: (1) artificially cloned fragment of the target gene DNA, containing annealing sites for the primers used for evaluation of the target gene expression (Lole and Arankalle, 2006); (2) genomic DNA (Cuscó et al, 2002; (Zhao et al, 2006). Genomic DNA is the most universal since it represents all the genes of an organism (Cuscó et al, 2002;Kulikov et al, 2005). Furthermore, calibration curves that are obtained using genomic DNA are far more stable than those obtained using amplicons, which allows comparing results of different experiments.…”