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Forensic genetics (Evidence Collection (reference samples from suspects…

- - - - used to localize dry semen stains on different substrates.
        
        In certain conditions semen and some other body fluids (saliva, vaginal fluid, urine) fluorescence in the UV light.
        
        Soaps and cosmetics can give unspecific fluorescence – artefacts.
        
        Preliminary test for semen presence.
        
        detection with UV light: emission 450nm, filter 550nm
    - -  Enzyme secreted by cells that line the prostate into seminal plasma in high concentrations.
         concentration in semen is 400x higher than in other body fluids (blood, saliva, sweat, urine).
         Very stable in stains (many years)
         SAP in vagina can be detected 5-6 days after last intercourse
         false positives!
        vaginal secretions (VAP)
        yeast and fungi
        plants such as cabbage, brussel sprouts, broccoli and cauliflower stem juice
         SAP has the ability to catalyze the hydrolysis of organic phosphates which forms a product that will react with chromogen to cause a colour change.
         SAP activity can be detected either using reagent-saturated papers (e.g. PhosphatesmoTM) or sodium alpha naphthylphosphate and Brentamine Fast Blue solution.
  - - - at least one sperm gives a proof of semen presence
        
        Lack of sperm does not mean that semen is not present !!!
        
        Time Intervals For Sperm Recovery in Living Sexual Assault Victims*
        
        the best confirmation of the presence of semen.
        
        Two common staining methods are: haematoxylin with eosin and the Christmas tree staining (stains heads red and tails green).
      - Sperm stability:
        depends on the numer of sperm cells in ejaculate,
        on body surfaces – stable for many days,
        on underwear, bedding and clothing - many months
    - - Prostate Specific Antigen:
         protein found in very high levels in seminal fluid
         Less sensitive than (SAP) test
         fewer false positives than the SAP test
         Urine, breast milk and sweat glands contain PSA but below forensic limits of detection.
         Present in vasectomised mens’ semen
         Antibody-antigen reaction test – immunochromatographic test
    - - • Proteins present in seminal fluid in high concentration .
        • Test gives positive results in cases of azoospermia, oligospermia and vasectomy.
- - - - sensitive and not specific.
         tests produce visible colour or result in release of light (chemiluminescecne)
        both tests rely on catalytic properties of blood (heme)
         positive results of presumptive tests do not indicate that blood is present !!!
        
        take advantage of the peroxidase- like activity of the haem group. Haem catalyses the hydrolysis of hydrogen peroxide, which in turn leads to the oxidation of the target compound, resulting in colour change.
      - Examples
        
        Producing colour reaction:
        – Benzidine (Adler’s Test)
         First screening test for blood (1904)
         Reaction carried out in ethanol/acetic acid solution
         Green color produced which sometimes turns to brown
         Very sensitive
         Benzidine is carcinogen
        – Phenolphthalein (Kastle-Meyer Test)
         commonly used today
         phenolphthalein – acid-base indicator
         less sensitive than benzidine test
         bright pink color produced
        – O-Toluidine
        – Tetramethylbenzidine (TMB)
        
        Using chemiluminescence – Luminol
         more value in locating and defining areas of possible blood than specifically identifying it
         spray chemical mixture of luminol observe the result in darkness
         catalytic activity of heme accelerates oxidation of luminol producing blue-white to yellowish-green light if blood present
         extremly sensitive – can detected blood present under wallpapers and areas pained up
    - - specific and moderately sensitive (100% certainty of blood presence)
        
        Not as sensitive as presumptive tests but give 100% proof of blood presence.
      - **Antibody tests – Immunochromatographic tests:
        most common**
        use monoclonal antibodies against
        • anti-glycophorine A antibody
        • anti-human haemoglobin A antibody
      - Spectrophotometric tests (main abs. peaks at 415nm and 560—570nm)
      - Microspectroscopic tests, (Teichmann and Takayama tests)