Presentation is loading. Please wait.

Presentation is loading. Please wait.

Lecture 4: Identification of Semen.  Biological characteristics of semen  Spermatozoa  Detection of semen  Presumptive vs confirmatory tests  Presumptive.

Similar presentations


Presentation on theme: "Lecture 4: Identification of Semen.  Biological characteristics of semen  Spermatozoa  Detection of semen  Presumptive vs confirmatory tests  Presumptive."— Presentation transcript:

1 Lecture 4: Identification of Semen

2  Biological characteristics of semen  Spermatozoa  Detection of semen  Presumptive vs confirmatory tests  Presumptive tests for semen  Detection of sperm  “Christmas Tree” stain  Confirmatory test for semen 2

3  Typical ejaculation  2-5 ml of semen, 160 million sperm ▪ 3 pg DNA/sperm = 480,000 ng DNA/ejaculate ▪ Only 1 ng DNA needed for STR typing!  Seminal fluid ▪ Medium for ejaculation ▪ Enzymes and other proteins ▪ Acid Phospahatase (AP), Prostate Specific Antigen (PSA), and semenogelin  Sperm cells- Spermatozoa 3

4 4

5  Semen is an extremely good source of DNA  The best! BUT…  Not all semen stains contain sperm  Vasectomy- blocks sperm from being ejaculated ▪ Semen still produced ▪ DNA typing probably not possible  Infertility ▪ Depending on severity, DNA typing may be possible 5

6  Three distinct regions:  Head – acrosome and nucleus (with haploid DNA)  Middle Piece (mitochondria)  Tail (flagella; mobility) 6

7  Presumptive tests  Fast, easy, inexpensive  Great for screening evidence to find possible stains  Usually detect enzymes specific to the body fluid  False positives (hence “presumptive”) ▪ Open to attack in court  Confirmatory tests  Not available for most body fluids ▪ Main exceptions are semen and blood 7

8  Semen fluoresces under ALS  UV light ▪ long-wave = “Woods Lamp” = 365 nm  Crime Lite (500 nm)  Lots of false positives 8 Alternative light source

9  Acid phosphatase enzyme  Advantages ▪ High levels in fresh semen stains ▪ Very fast, inexpensive ▪ Can be done in the field  Limitations ▪ Activity may be weak or absent in older stains ▪ Also present at low levels in vaginal fluid and bacteria ▪ Not species-specific 9

10  AP assay  AP liberates naphthol from alpha-naphthol and the naphthol then reacts with brentamine to form a purple-colored dye 10 sodium phosphate + naphthol α-naphthyl acid phosphate monosodium salt Acid phosphatase Coupling reaction Purple azo dye napthol + Brentamine

11 11  Overlay method ▪ Spray a Whatman paper circle with distilled water ▪ Lay the paper down over the suspected semen stain ▪ Leave in contact with stain seconds ▪ Remove paper circle from stain and spray with AP spot solution ▪ Look for a rapid color change to purple Positive acid phosphatase overlay assay

12  Spot test method ▪ Wet sterile cotton swab with distilled water ▪ Roll swab across stain ▪ Saturate swab with AP solution 12

13  MUP  More sensitive than acid phosphatase  AP catalyzes the removal of the phosphate residue on the substrate 4-methylumbelliferone phosphate (MUP), which generates fluorescence under UV light  Filter paper overlay ▪ Filter paper placed in contact with putative semen stain and then removed and taken to dark room ▪ Sprayed with MUP ▪ Fluorescence detected with UV lamp 13

14 14

15  Prostate-specific antigen (PSA)  Major protein in seminal fluid  Also detected in urine, fecal matter, sweat, milk but at much lower levels  Half-life of dried stain: 3 years  Hydrolyzes semenogelins (seminal vesicle specific antigens)  Detected with immunochromatographic test strip assay 15

16  Semenogelins  Higher concentration in seminal fluid than PSA  Not found in urine, milk, sweat  Greater specificity for semen than PSA  Detected with immunochromatographic test strip assay 16

17  Immunochromatographic test strip assay for semenogelin  Rapid and simple  Specificity still under debate  Rapid Stain Identification (RSID-Semen) ▪ Independent Forensics 17

18 18 T Positive RSID™ semen test human semenogenlin monoclonal gold-labeled murine anti human semenogelin antibody to epitope 1 monoclonal unlabeled murine anti human semenogelin antibody to epitope 2 polyclonal unlabeled goat anti murine antiglobulin T C

19 19 T C Negative RSID™ semen test

20  Microscopic examination  “Christmas Tree” stain ▪ Nuclear Fast Red stains nuclei red ▪ Picroindigocarmine stains tails green 20 Acrosomes don’t stain well in primate sperm

21 21


Download ppt "Lecture 4: Identification of Semen.  Biological characteristics of semen  Spermatozoa  Detection of semen  Presumptive vs confirmatory tests  Presumptive."

Similar presentations


Ads by Google