Presentation on theme: "Semen & Rape. List the laboratory tests necessary to characterize seminal stains Explain how suspect blood and semen stains are properly preserved."— Presentation transcript:
Semen & Rape
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.
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
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
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
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
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
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
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.
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
1. What test is used to locate and characterize seminal tissue? Why is it useful? 2. Differentiate between oligospermia and aspermia 3. What protein is indicative of semen and what two tests are used to detect this protein? 4. Why must a rape victim stand on a sheet of paper while disrobing for forensics analysis? 5. Besides swabbing for semen constituents, what other bodily fluids should be collected from a rape victim during a medical examination? 6. What items should be collected from the suspected perpetrator of sexual assault? (at least 4 things) 7. How long do motile sperm generally survive in the vaginal cavity of a living female? 8. How long do non-motile sperm generally survive in the vaginal cavity of a living female?