This study tested the ability of commercial and inhouse Y-STR systems to provide DNA profiles from cervicovaginal swabs submitted 3 or more days after intercourse.
The testing of samples from three female volunteers showed that full Y-STR profiles were obtained 3-4 days after intercourse, using both commercial and inhouse systems. Profiles were also obtained 5-6 days after intercourse, although partial profiles rather than full profiles were more likely after this period. Almost without exception, more complete profiles were obtained when DNA from the sperm fraction of a differential lysis method was amplified compared to the amplification of relatively large quantities (approximately 300 ng) of admixed male/female DNA. The incorporation of a sample post-PCR purification process significantly increased the ability of the testing to obtain Y-STR profiles, particularly from 5-6-day postcoital samples. The two commonly used commercial Y-STR systems, AmpFlSTR Yfiler and PowerPlex Y, performed very well. They performed better than the inhouse "benchmark" systems with 6-day postcoital samples, since no profiles were obtained with the inhouse Multiplex I (MPI) and Multiplex B (MPB) systems. The third commercial system evaluated, Y-Plex 12, did not perform well on samples submitted more than 4 days after intercourse. The three female volunteers each recovered two samples for testing at various time points after separate acts of sexual intercourse, using sterile cotton tipped applicators. The points for sample collection were 72, 96, 120, 144, and 168 hours after intercourse. The women were instructed to take the cervicovaginal swabs by brushing the cervix multiple times for at least 30 seconds at each time interval. This report describes DNA isolation and purification, DNA quantitation, standard PCR conditions, and post-PCR clean-up. 2 tables, 3 figures, and 34 references