12.5 Notes

1. 12.5 Notes Semen & Rape

2. Objectives • List the laboratory tests necessary to characterize seminal stains • Explain how suspect blood and semen stains are properly preserved for laboratory examination • Describe the proper collection of physical evidence in a rape investigation.

3. Characterization of Semen • Normal male releases 2.5 to 6-mL during ejaculation • Each mililiter contains 100 million+ spermatozoa • Sperm are indicative of semen • Oligospermia – low sperm count • Aspermia – no sperm in seminal fluid

4. Forensic examination for seminal stain • 2 step process • Stain must be located usually using an acid phosphatase color test • Acid phosphatase = enzyme secreted by the prostate gland into seminal fluid • Concentrations are up to 400x greater than in other bodily fluid • Turns purple when reacted with acidic solutions • Fluoresces under UV light with 4-methyl umbelliferyl phosphate (MUP) • Subject to test to prove its identity

5. Semen • Protein p30 or prostate specific antigen (PSA) is a protein unique to seminal plasma • Stimulates the production of polyclonals when injected into a rabbit • Currently a new technique is used that places a monoclonal PSA antibody on a porous membrane which then moves toward a polyclonal PSA also on the same membrane

6. Rape Evidence • Seminal constituents on a rape victim are important evidence that sexual intercourse took place • Their absence does not necessarily mean that a rape did not occur • Physical injuries such as bruises and bleeding tend to confirm that a violent assault occurred • Forceful physical contact between victim and assailant may results in the transfer of physical evidence – blood, semen, hairs, fibers

7. Collection of Rape Evidence • To protect the evidence, all outer garments and undergarments of the persons involved are carefully removed and packaged separately in paper bags • A clean bed sheet and clean paper sheet are placed on the floor and the victim removes all their clothing • Paper collects any loose foreign material falling from the clothing • Each piece of clothing is individually bagged to avoid cross-contamination • Paper is carefully folded to keep all foreign material inside

8. Collection of Rape Evidence CONT…. • Items suspected of containing seminal stains are carefully handled • Folding the article can cause the stain to flake off • Rubbing against the surface of the packaging material can also cause flaking • Analysts try to link seminal material to donor(s) using DNA typing • Individuals may transfer their DNA types to a stain through perspiration, so special care must be taken to minimize direct personal contact with the stain

9. Collection of Rape Evidence CONT…. • Rape victim undergoes a complete medical examination as soon as possible following the assault • Physical evidence is collected by trained personnel • It includes: pubic combings, pubic hair standard/reference sample, external and internal genital skin area swabs (vaginal, cervical, rectal, oral), head hairs, blood sample, fingernail scrapings, all clothing, urine specimen.

10. Collection of Rape Evidence CONT…. • From the suspect, physical evidence is also collected. • It includes: all clothing, pubic hair combs, pulled head and pubic hair standard/reference samples, penile swab, and blood sample or buccal swab for DNA

11. 12.5 Questions • What test is used to locate and characterize seminal tissue? Why is it useful? • Differentiate between oligospermia and aspermia • What protein is indicative of semen and what two tests are used to detect this protein? • Why must a rape victim stand on a sheet of paper while disrobing for forensics analysis? • Besides swabbing for semen constituents, what other bodily fluids should be collected from a rape victim during a medical examination? • What items should be collected from the suspected perpetrator of sexual assault? (at least 4 things) • How long do motile sperm generally survive in the vaginal cavity of a living female? • How long do non-motile sperm generally survive in the vaginal cavity of a living female?