A comparative experimental study on the collection and analysis of DNA samples from under fingernail material

Abstract

In cases of murder and rape where there is physical contact between the perpetrator and the victim, analysis of the victim’s nail material is quite valuable. Although it is possible that the foreign DNA detected in the fingernail material does not belong to the perpetrator of the incident, ıf it belongs to the perpetrator of the incident, it may provide useful findings for solve the incident. Fingernail material collected after the incident often contains resulting in mixed DNA. The efficiency of sample collection procedures is of particular importance, as this process may pose some problems in the interpretation of autosomal STR analyses used for the identification of the individual or individuals. The aim of this study is to compare 3 different fingernail material collection procedures (thick-tipped swabbing and thin-tipped swabbing and nail clipping) to determine the most efficient sample collection procedure and to contribute to routine investigations to identify the assailant in forensic cases. In our study, under fingernail material was collected from 12 volunteer couples by three different methods. To help comparing the efficiency of the three different methods, the profiles obtained were classified based on the number of female and men alleles detected. Obtained STR profiles, while nail clipping yielded 58.3% (n:7) ‘High level DNA mixture’ as a profile containing 12 or more than 12 female alleles, 75% (n:9) of the samples taken with cotton-toothpick swabs (thin-tipped) yielded ‘Full Male Profile’. In conclusion, our study shows that cotton toothpick swabs (thin-tipped) are the most efficient method for determining the male DNA profile among three different fingernail material collection procedures. We suggest that using thin-tipped swabs produced in a specific standard instead of the commonly used size swabs that are frequently used in routine crime investigations to identify perpetrator from fingernail material may improve efficiency of processing the nails and evaluation of the evidence.