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.

Validation and uses of a Y-chromosome STR 10-plex for forensic and paternity laboratories.

Y-chromosome short tandem repeats (Y-STRs) provide valuable information in cases of rape and questioned paternity, and they allow for the genetic identification of male lineages. The present study validated a Y-STR 10-plex on the ABI PRISM 3100 Genetic Analyzer for use in forensic and paternity laboratories at Orchid Cellmark. Following optimization of the polymerase chain reaction, father-son pairs were analyzed to ensure that each pair generated identical haplotypes. This study demonstrated that the 10-plex is sensitive to 0.125 ng of input DNA and that female samples mixed with male samples did not interfere with Y-STR haplotyping. In a sample of 525 males, there were three instances of locus multiplication, two at DYS19 and one at DYS435. Overall, haplotype diversity was 0.996, suggesting that the 10-plex can effectively distinguish among male lineages.