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Forensic Biology by Richard Li

Chapter 8: Identification of Semen. Forensic Biology by Richard Li. Biological Characteristics. Typical ejaculation 2-5 ml of semen Seminal fluid Seminal vesicle fluid- 60% of ejaculate Prostatic fluid secretions- 30% of ejaculate Acid Phospahatase (AP) & Prostate Specific Antigen (PSA)

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Forensic Biology by Richard Li

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  1. Chapter 8: Identification of Semen Forensic Biologyby Richard Li

  2. Biological Characteristics • Typical ejaculation • 2-5 ml of semen • Seminal fluid • Seminal vesicle fluid- 60% of ejaculate • Prostatic fluid secretions- 30% of ejaculate • Acid Phospahatase (AP) & Prostate Specific Antigen (PSA) • Epididymis and bulbourethral glands- each 5% • Sperm cells- Spermatozoa Forensic Biology by Richard Li

  3. Biological Characteristics • Vasectomy- block spermatozoa • Still produces ejaculate with seminal vesicle fluid and prostatic fluid • Oligospermia- low sperm count • Aspermia- no sperm Forensic Biology by Richard Li

  4. Spermatozoa • Three distinct regions: • Head • Middle Piece • Tail Forensic Biology by Richard Li

  5. Acid Phosphatase • Optimal activity in acidic pH environment • Present in lysosomes • Prostate AP • Half-life at 37 degrees C: 6 months Forensic Biology by Richard Li

  6. Prostate-Specific Antigen • Major protein in seminal fluid • Also detected in urine, fecal matter, sweat, milk • Half-life of dried stain: 3 years Forensic Biology by Richard Li

  7. Seminal Vesicle Specific Antigen • Semenogelins • I & II • Higher concentration in seminal fluid than PSA • Not found in urine, milk, sweat Forensic Biology by Richard Li

  8. Lighting Techniques • Locating dried stains • UV light • Argon laser • Alternate light source (ALS) • 450-495 nm Forensic Biology by Richard Li

  9. Colorimetric Assay • AP catalyzes the removal of the phosphate group from a substrate • Positive= purple color Forensic Biology by Richard Li

  10. Fluororimetric Assay • More sensitive than colorimetric • AP catalyzes the removal of the phosphate residue on the substrate 4-methylumbelliferone phosphate which generates fluorescence under UV light Forensic Biology by Richard Li

  11. Confirmatory Tests • Microscopic examination • Christmas Tree Stain • Laser capture microdissection • Identification of prostate-specific antigen • Radial immunodiffusion • Rocket immunoelectrophoresis • CIE • ELISA • Imunnochromatographic assays Most sensitive Forensic Biology by Richard Li

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