DNA Contamination

A few confounders, i.e. transcriptional “noise” introduced by DNA contamination or unprocessed pre-mRNA transcripts, need to be considered within the analysis of IR events. IRFinder detects DNA contamination by computing the ratio of reads mapped to intergenic regions to the amount of reads that mapped to coding regions. In case, the ratio is above 10%, IRFinder emits a warning informing the user that the sample might not be suitable for IR detection. When performing PCR amplification it is critical to be aware of potential sources of DNA contamination and to employ procedures to ensure contamination-free working conditions. The power of PCR to amplify very small quantities of DNA producing detectable amplification products demands that special care be taken to stop cross-contamination between different samples. This is especially true for PCR targets expected to be present in low amounts because greater efforts are usually required to amplify those sequences. Once conscious of DNA contamination while brushing fingermarks, using an equivalent code of colours for texts and frames shows the available fingerprint development sequence for nonporous surfaces. Once again, the crime scene sequence is shown in the blue frame, underlining that the iodine process, the VMD, and the SMD/MMD are also available alternatives depending on the nature of the surface. VMD is, indeed, better carried out on nonporous surfaces than on porous ones.