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Y-STR profiles using the Promega PowerPlex(®) Y system were attempted on multiple vaginal swabs collected at four, six and eight days after intercourse from female partners of 11 couples. At four days postcoitus, full composite profiles (where swabs yielded confirmed alleles at all 11 loci) were obtained for five of the 11 couples and 78% of all possible alleles summed for all couples were confirmed (able to be duplicated in different swabs). Results for composite profiles for all couples taken at six days after intercourse showed that 53% of all alleles summed for all couples were confirmed. Only one couple yielded a full composite profile at six days after intercourse. Composite profiles from swabs taken at eight days after intercourse for all couples confirmed only 44% of all possible alleles summed for all couples. At eight days postcoitus, no couple yielded a full composite profile and the largest number of confirmed alleles for any couple was eight. However, one of 44 individual swabs taken from all couples combined at eight days postcoitus yielded a 10-locus profile. Composite partial profiles from the eight-day postcoital set with confirmed results at a minimum of five loci (8 of 11 couples) yielded haplotype frequencies from 0.000323 to 0.125862 using the Y chromosome haplotype reference database, suggesting that meaningful Y-STR information can still be obtained at much extended postcoital intervals.

In this study, useful genetic information from male donors was obtained on vaginal swabs taken from female volunteers after male digital vaginal penetration in a time frame relevant to a sexual assault investigation. Vaginal swabs were collected from eight volunteers at intervals of 1, 6, 12, 24, and 72 hours after digital vaginal penetration. DNA was extracted from collected swabs and subsequently genotyped using a commercially available Y-chromosome short tandem repeats (Y-STR) multiplex kit. Fifty-eight vaginal swabs were collected and analyzed in the study. Composite Y-STR profiles from all combined volunteers showed that 85% of all possible alleles were detected at the 1-hour interval, 77% of all possible alleles were detected at the 6-hour interval, 73% of all possible alleles were detected at the 12-hour interval, 66% of all possible alleles were detected at the 24-hour time interval, and 71% of all possible alleles were detected at 72 hours after digital vaginal penetration. Results indicate that a viable possibility exists that probative Y-STR profiles, useful for investigative purposes, can be obtained from vaginal swabs taken from subjects exposed to digital penetration at time intervals up to 72 hours postpenetration.

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