Análise molecular com Y-STRs em amostras biológicas sem espermatozoides coletadas de vítimas de estupro


IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia




The detection of sperm cells in samples collected from victims of sex crimes confirms the occurrence of the sexual act, while its absence usually closes biological research, leaving a gap as to the authorship of the crime and even how to define whether there was a crime. In sex crimes, however, there is the possibility that the collected vaginal material does not contain rapists sperm cells (e.g., azoospermy, condom use, practice of coitus interruptus), but other male cells like epithelial cells or leukocytes may be present in seminal fluid. In these cases, the isolation of male cells by differential extraction technique is not possible and the identification of authorship by DNA analysis is impaired, since the amplification for authosomal STRs in samples with a mixture of DNA with ratios equal to or greater to 50:1, the genetic profile of minority donors is not commonly displayed. Molecular techniques using Y-STRs are a powerful tool for the identification of male profiles in these cases. In order to evaluate the effective amplification of Y-STRs in samples with mixture of male and female DNA, looking for relate the results obtained with the history of each case and devise a strategy for action in similar cases in the future, six hundred incidents of rape victims whose samples were negative in study sperms cells were analyzed. We selected 150 female victims cases when the history pointed to possible occurrence of rape with penetration and ejaculation or, whose communication was actually held up to 4 days after the criminal fact. Following the quantification, it was found that in 43% of selected cases was detected the presence of male DNA source, and in 83% of the samples the proportion of female DNA in relation to the amount of male DNA was greater than 100:1. The samples with male DNA were amplified for 16 Y-STRs (DYS456, DYS389 I, DYS389 II, DYS392, DYS393, DYS438, DYS390, DYS458, DYS19, DYS385, DYS391, DYS439, DYS635, Y_GATA_H4, DYS437 and DYS448) and the profiles obtained were classified into four types, defined according to the number of Y-STRs loci with amplification product, ranging from insufficient haplotype (up to five Y-STRs loci) to complete haplotype. Detection of prostate specific antigen (PSA) was performed in all selected samples and the results are conflicting with the quantification of male DNA in 28.6% of them. These results confirm previous work performed by other authors and moreover changed the routine of the Instituto de Pesquisa de DNA Forense of Civil Police of the Federal District in Brazil, in order to define whether or not the genetic analysis of samples collected from rape victims in cases without sperm cells.


espermatozóides estupro dna biotecnologia genetica rape sperm cell dna y-strs

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