Determination of the variables affecting mixed MiniFiler™ DNA profiles

The interpretation of mixed DNA profiles presents additional challenges for the forensic scientist. There has been a broad based call for transparency in the process of interpretation of all evidence including mixed DNA profiles. This interpretation is greatly facilitated by a sound understanding of the variability in peak heights for the two peaks of a heterozygote, in the sizes of stutter peaks and in the variability in peak heights across loci. This study examines single source and mixed DNA profiles to assess this variability. The relative variability in peak height between the two peaks of a heterozygote and in the peak heights across loci becomes greater as the peaks themselves become smaller. This is consistent with findings from other multiplexes. This variability appears larger in the MiniFiler™ system at 30 cycles than, for example, in the Identifiler™ system at 28 cycles and this difference is largely explained by the two extra cycles of amplification. Stutter peaks appear no larger in the MiniFiler™ system at 30 cycles than in the Identifiler™ system at 28 cycles.