Almost two-thirds of cases pursued with forensic DNA testing involve sexual assault evidence. Hundreds of millions of sperm are typically ejaculated in several milliliters of seminal fluid. Semen stains can be characterized with visualization of sperm cells, acid phosphatase (AP) or prostate specific antigen (PSA or p30) tests.
A microscopic examination to look for the presence of spermatozoa is performed in some laboratories on sexual assault evidence. However, aspermic or oligospermic males have either no sperm or a low sperm count in their seminal fluid ejaculate. In addition, vasectomized males will not release sperm. Therefore tests that can identify semen-specific enzymes are helpful in verifying the presence of semen in sexual assault cases.
Acid phosphatase is an enzyme secreted by the prostate gland into seminal fluid and found in concentrations up to 400 times greater in semen than in other body fluids (Sensabaugh 1979, Saferstein 2001). A purple color with the addition of a few drops of sodium alpha naphthylphosphate and Fast Blue B solution or the fluorescence of 4-methyl umbelliferyl phosphate under a UV light indicates the presence of AP. Large areas of fabric can be screened by pressing the garment or bed sheet against an equal sized piece of moistened filter paper and then subjecting the filter paper to the presumptive tests.
Alternatively systematic searches can be done over sections of the fabric under examination to narrow the semen stain location with each successive test (Saferstein 2001).
Prostate specific antigen was discovered in the 1970s and shown to have forensic value with the identity of a protein named p30 due to its apparent 30 000 molecular weight (Sensabaugh 1978). p30 was initially thought to be unique to seminal fluid although it has been reported at lower levels in breast milk (Yu and Diamandis 1995) and other fluids (Diamandis and Yu 1995). PSA varies in concentration from approximately 300-4200 ng/mL in semen (Shaler 2002). Seratec (Goettingen, Germany) and Abacus Diagnostics (West Hills, CA) market PSA/p30 test kits that are similar to home-pregnancy tests and which may be used for the forensic identification of semen stains (Hochmeister et al. 1999, Simich et al. 1999).
Was this article helpful?
Discover Simple Techniques to Help Control Your Stutter. Stuttering is annoying and embarrassing. If you or a member of your family stutters, you already know the impact it can have on your everyday life. Stuttering interferes with communication, and can make social situations very difficult. It can even be harmful to your school or business life.