The utility of Y-STR profiling in four-, six- and eight-day postcoital vaginal swabs

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.