A plot showing the quality of pre-amplification. Successfully pre-amplified samples lie bellow the quality threshold, which corresponds to ΔΔCq = 1.5 (expression differential). The quality of pre-amplification gets worse with increasing number of pre-amplification cycles. During cycles 15 and 18 only small number of samples amplified with low copy gene RND1 (lowest concentrations) and high copy gene FKBP are affected. At cycles 21 and 24, the quality of pre-amplification is affected in all genes to some extent. The least affected gene is CD83, the most affected are high copy genes.