Isolation and identification of male and female DNA on a postcoital condom

Identification of male perpetrators of sexual assault may be made from cells and fluids recovered from postcoital condoms. To date, the focus has been on identifying the person who had worn the condom.

To describe a method for scientifically identifying both the male and female participants in a sex act by employing polymerase chain reaction-based technology on swabs taken from the internal and external surfaces of a condom. Fluorescence in situ hybridization may be used to screen for the presence of female cells on a condom.

Swabs were taken from the internal and external surfaces of a condom 8 hours postcoitus. DNA was isolated from each swab through standard organic extraction. Extracted DNA was amplified for 8 different genetic loci using the Promega PowerPlex kit and the sex identification amelogenin marker. Amplified samples were electrophoresed on precast sequencing gels and analyzed fluorescently using a Hitachi FMBIO 2 fluorescent scanner and software. Each DNA sample obtained from the condom was compared with male and female buccal controls. At the time of collection, air-dried slides were prepared from the swabs for subsequent multicolor fluorescence in situ hybridization using dual X- and Y-chromosome probes with 4'-6-diamidino-2-phenylindole (DAPI) counterstaining.

A pure sample of female DNA was isolated from the external surface of the condom as determined by exclusive amplification of the X-chromosome-specific 212-base pair amelogenin marker. Swabs taken from the internal surface yielded DNA originating from the male participant. Identification was conclusive at 8 of 8 genetic loci. Fluorescence in situ hybridization identified pure populations of male epithelial cells from the internal surface of the condom and female cells from the external surface.

Cells shed from a female during sexual intercourse can be retrieved from the external surface of a condom following sexual intercourse. Fluorescence in situ hybridization can be used to screen for the presence of female cells, and positive identification of the female sexual partner can then be made using polymerase chain reaction-based methods. We suggest that swabs taken from both surfaces of a condom used during sexual assault may be used to provide information that will definitively link the victim to the suspect.