Estudo de perfis genéticos obtidos a partir de amostras de DNA produzidas por contato

DNA analysis has been used as a tool of criminal investigation and for producing forensic evidence. This kind of exam has been increasingly requested, even in situations where the amount of DNA present in the samples is very small. For example, samples of touch DNA, which consists of objects manipulated or touched by human skin that have small amounts of cells deposited on its surface, potential targets to DNA analysis. In this kind of sample, a great challenge is to identify the best locations for sample collection, since the biological material is not easy to identify. The fingerprint revelation technique uses fingerprint powders to reveal latent fingerprints allowing the identification surfaces touched by human skin. The aim of this study was to evaluate the possibility of using the fingerprint powders as screening tools for collecting biological material in touch DNA samples, obtaining good quality genetic profiles. The first step was to study the amount of powder adhered to the impressions produced by the different parts of the hands and the correlation between the amount of powder and the amount of DNA recovered. Next, the influence of fingerprint powder on laboratory procedures involved in DNA analysis was evaluated. The inhibitory effect of fingerprint powder in the PCR reaction was tested followed by the effect of different extraction methods on the inhibition. One DNA purification step was even included to improve the results. Finally, five different objects related to crimes: firearms, ammunition cartridge, kitchen knife, steering wheel and gear shift were proceeded to DNA analysis. The results showed that the amount of fingerprint powder recovered differed according the region of the hand which produced the fingerprint and the amount of adhered powder was directly related to the amount of DNA obtained. The fingerprint powder had a significant inhibitory effect on the PCR reaction. The methods of DNA extraction decreases the inhibitory effect, but it remains relevant. The purification procedure does not completely eliminate the inhibitory effect, but reduces an intensity that does not completely compromise the obtaining genetic profiles. In the five tested objects, it was possible to collect good amounts of DNA in the steering wheel, and in reasonable quantities in the firearms, gear shift and kitchen knife. The cartridge ammunition was the only object which was not possible to recover DNA in sufficient amount to produce quality genetic profiles. Therefore, we conclude that fingerprint powders can be used as tools for choosing the right regions to collect biological material in touch DNA samples. Even considering its inhibitory effect on the PCR reaction, samples collected along with fingerprint powders are able to produce genetic profiles with sufficient quality for genetic analysis.