Mixture interpretation: Experimental and simulated reevaluation of qualitative analysis

Abstract

We present here analytical data using the 15 STR typing (Identifiler) kit regarding heterozygote balance in experimental DNA samples including one or two persons. Surprisingly, the allelic imbalance was observed even in samples consisting of only one person but adequate DNA for the standard protocol. The variance of heterozygote balance was more expanded in two-person mixtures than in one-person samples. Therefore, it is not suitable to use allelic peak heights/areas for estimating the genotypes of the contributors such as the quantitative analysis. We also reevaluated the effectiveness of qualitative analysis by simulation, i.e. consideration of the probability of all possible genotype combinations from the typing results of a mixed DNA sample. As demonstrated, the qualitative analysis using 15 STR loci is still extremely effective even in a mixture from two or three individuals.