Journal of Forensic Research

The Applicability of Autosomal Short Tandem Repeats Genotyping for Minor Contributor DNA Profiling from Mixed Saliva Samples

Abstract

Gabriela Repiská, Jaroslava Durdiaková, Natália Kamodyová and Gabriel Minárik

Objective: In our previous study focused on Y-chromosome sequence identification and genotyping we revealed the possibility of male minor fraction identification and genotyping in mixed salivary samples obtained from females 60 and 30 minutes after intense kissing. The aim of this study was to test the applicability of an autosomal STR (aSTR) profiling kit for male fraction detection and genotyping on salivary samples obtained from females 1 – 60 minutes after intense kissing.
Methods: The aSTR typing was performed on DNA samples originated from buccal swab and saliva samples collected from 12 heterosexual pairs before and after 2 minutes of intense kissing, respectively. The success of minor contributor allele identification was quantified as the ratio between Counts of Identified Obligatory Alleles and Counts of Potentially Identifiable Obligatory Alleles. For the estimation of proportion of minor contributor DNA the Y/X Amelogenin peak height ratio was used.
Results: In samples collected immediately after kissing has stopped the Amelogenin Y/X signal ratio varied between 0 and 63%. The ratio was associated with aSTR profiling success as in samples with higher than 7% Y/X ratio more than 80% of minor contributor male alleles were identified. In one sample collected 5 minutes after kissing expected male signal was detected with Y/X ratio reaching 15% and 77% of obligatory male alleles were identified. In comparison of previously and currently utilized methods for minor contributor male DNA detection and identification the concordance in their performance was recorded. Conclusion: We confirmed that in salivary mixtures, female saliva DNA analysis with use of aSTR genotyping kit is possible, but with limited effectiveness. The male admixture was detected with aSTR genotyping kit in salivary samples collected up to 5 minutes after intense kissing.