Many crimes are associated with finding very few traces of saliva samples in the crime scene. DNA extraction from forensic samples normally causes loss of some DNA. In order to study the possibility of substituting the initial DNA extraction step from very scarce forensic saliva samples by a direct PCR, different amounts of saliva samples (0.5 μL, 1 μL, and 3 μL) were collected and applied into the PCR directly or by routine extraction DNA method. Fifteen autosomal loci of short tandem repeats (STRs) were amplified with PCR, that are D3S1358, TH01, D21S11, D18S51, Penta E, D5S818, D13S317, D7S820, D16S539, CSF1PO, Penta D, vWA, D8S1179, TPOX, and FGA, in addition to a gender identification marker, Amelogenin. Loading 0.5 μL saliva sample directly into the PCR revealed higher scale of peak height in 11 - 13 loci than in case of a prior DNA extraction step. Increasing the amount of saliva samples led to a gradually decrease in the scale of peak heights, till a complete loss of amplification. The results indicated that direct PCR without DNA extraction and with only very few amount of saliva (0.5 μL) gives better results than performing an initial, pre-PCR DNA extraction step. This leads to: i) saving sample processing time, ii) reducing at least 25 % of the processing costs, and iii) enhancing the detection efficiency for more than 50 % of the studied loci.
Key words: Forensic Technique, DNA Detection, Saliva, PCR.
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