Analysis of non-suspect samples lacking visually identifiable sperm using a Y-STR 10-plex

Y-STRs are valuable in the investigation of sexual assaults in which autosomal STR genotype interpretation is challenging. To detect male DNA from compromised sexual assault evidence, 45 non-suspect samples were differentially extracted and analyzed with 10 Y-STRs. These samples were positive for the presence of human seminal fluid, but were negative for spermatozoa by microscopic examination. Y-STR data were obtained in approximately 86.2% of the epithelial or sperm fractions. On samples yielding incomplete profiles, results were obtained on an average of 5 loci per sample. The inability to obtain results may be due to insufficient amplifiable male DNA, PCR inhibition, or unfounded accusations of sexual assault. This study indicates that it is possible to obtain a male STR profile even in the absence of visually identifiable spermatozoa. Furthermore, Y-STR loci should become components of CODIS if they are to be used in solving non-suspect sexual assaults.