Since the introduction of the term low copy number DNA, also referred as low template DNA, touch DNA or trace DNA analysis, it has quickly become focal point of forensic DNA testing as well as other DNA based studies. Low template DNA (ltDNA) samples can be described as the samples which involve single source samples with template DNA in concentrations below 100 picograms (pg). Due to sensitivity of ltDNA samples to contamination, it is of great importance to optimize performance of the

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... x STR systems and existing protocols to increase chance of successful analysis. The main objective of this study was analysis of 20 challenging samples (skeletal remains, cigarette buts, chewing gum, poorly collected buccal swabs etc.) mostly low template DNA samples, preliminarily profiled by PowerPlex® 16 multiplex STR systems and additionally processed with new generation multiplex STR kit PowerPlex® Fusion. Sample isolation was done using a standard phenol-chloroform method for bone samples and DNeasy® Blood and Tissue Kit for other forensic samples. PowerPlex® 16 (PP16), multiplex STR system and PowerPlex® Fusion (PP Fusion) were used for co-amplification of 15 and 24 autosomal STR loci respectively. Results of this preliminary study suggest that PP Fusion primer set is better optimized for the analysis of ltDNA samples, and it is more robust regarding presence of the potential PCR inhibitors.