This study's objective was to develop additional strategies for the recovery of male semen donor DNA profiles from samples obtained approximately 6 days post-coitus.
The ability to obtain an autosomal short tandem repeat (STR) profile of the semen donor from the reproductive tract of a living victim rapidly diminishes as the post-coital interval increases. This is of concern where victims of sexual assault provide vaginal samples several days after the incident. In order to overcome the technological impediments inherent in autosomal DNA typing with extended interval samples, the authors previously employed the use of Y chromosome STR profiling which, by targeting only male DNA, can eliminate masking of the male profile (by the victim's alleles) or critical polymerase chain reaction reagent titration (due to excessive female DNA). Thus, by using Y-STR profiling and additional enhancement strategies, the authors reported the ability to recover Y-STR profiles from samples collected 5 to 6 days after intercourse; however, the reproductive biology literature indicates that spermatozoa are found in the human cervix up to 7 to 10 days post-coitus. Thus, even with improved extraction and profiling techniques, the authors failed to routinely recover profiles from samples collected approximately 6 days after intercourse. The current study, however, used nested polymerase chain reaction and DNA concentration procedures that together maximized the recovery and targeting of male DNA. The authors demonstrated the ability to obtain semen donor Y-STR profiles in extended interval post-coital samples collected 6 to 9 days after intercourse. This approaches the recognized time limits of sperm residence in the cervico-vaginal canal as described in the clinical literature. (Publisher abstract modified)