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Biological Evidence

Biological Evidence. Serology. Serology- study of blood and other bodily liquids Semen Sweat Saliva Gastric Juices. Blood. Functions of Blood Transport of nutrients, wastes, and hormones Defense against pathogens Stabilization of body temperature Composition of blood

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Biological Evidence

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  1. Biological Evidence

  2. Serology • Serology- study of blood and other bodily liquids • Semen • Sweat • Saliva • Gastric Juices

  3. Blood • Functions of Blood • Transport of nutrients, wastes, and hormones • Defense against pathogens • Stabilization of body temperature • Composition of blood • Plasma: liquid portion of blood (46-63%) • Cellular Components • Red cells (erythrocytes) • White cells (leukocytes) • Platelets (thrombocytes)

  4. Types of Red Blood Cells • 1901: Blood typing discovered by Landsteiner through blood transfusions (transfer of blood into another’s blood stream) • Classification system: A, B, AB, O, Rh+, Rh- • Based on antigens on surface of red blood cell

  5. Blood & Forensics • Until 1990s, use of blood for ID based on blood typing assuming no 2 people have same blood (except twins) • > 100 factors, or antigens on red blood cells • Factors controlled by individual genetics • Now can use DNA typing as __________ evidence • ABO & Rh currently considered class evidence. Why? • Comparisons made by the product rule (of probability)

  6. Blood Probability Question • What is the probability that someone else in the population has this combination of antigens? • A positive, M-, N positive, S positive • Antigen Incidence in General pop’n A 42% B 12% AB 3% O 43% Rh 85% M 30% N 27% S 48%

  7. One more Question • Probability of O negative, M positive, N-, S- • Antigen Incidence in General pop’n A 42% B 12% AB 3% O 43% Rh 85% M 30% N 27% S 48%

  8. Is It Really Blood? • Questions to be answered when collecting (in order) • Is the sample blood? • Is the sample animal blood? • If animal blood, from what species? • If human blood, what type? • Can the sex, age, and race of the source of blood be determined?

  9. Question 1: Is it really blood? - test means not likely blood + test means blood Presumptive tests cause color change Tests rely on catalytic properties of blood ( hemoglobin presence) Kastle Meyer (Phenolphthalein) Luminol Chemical sprayed on carpet and furniture Slight phosphorescent light in dark where there are blood stains (and certain other stains) are present Emission of light (in dark room) is positive • Hemoglobin- peroxidase-like activity • Oxidize hydrogen peroxide and the free O will turn phenolphthalein bright pink Hemastix • Dipsticks easy to carry • When used at crime scene, turn green if blood

  10. Questions 2 & 3: Is the Sample Human or Animal Blood? • Precipitation Test- to determine if blood human or not • Based on rabbit antibodies to human blood • Blood placed in antiserum tube • Non-human blood reacts with antibodies in antiserum • Form precipitin band

  11. Question 4: If human, what is its type? • Test antigen of red blood cell • Stimulates body to make antibodies against it • If antibody matches antigen, RBC will agglutinate ( or clump)

  12. Interpreting Agglutination (clumping) • If clumps, that is the blood type • Coagulation (clumping) & hemolysis (cell burst) occurs if antigen comes in contact with antibody

  13. Blood Typing Punnett Squares • Blood Type A: AA or AO • Blood Type B: BB or BO • Blood Type AB: AB • Blood Type O: OO AB x BO OO x AB

  14. DNA • DNA- codes for blood type • Each person’s DNA different from each other ___________ characteristic • DNA found in nucleus of cells (except RBCs) • Individuals possess 2 forms of DNA • Nuclear DNA • Mitochondrial DNA (DNA from mom!)

  15. DNA: Cont’d • DNA contains • Sugar • Phosphate • Nitrogenous Base • Includes: A, T, C, G to form DNA alphabet • A –T • G - C • Sequence of letters unique to each individual Backbone

  16. DNA: Cont’d • Nucleotide: Sugar-phosphate backbone + nitrogenous base • Forensics- look at these sequences • Gene- different sequences of nucleotides • Encode for proteins • Structure of DNA: double helix Nucleotide

  17. Collecting DNA • Extract DNA from the sample

  18. Electrophoresis- separate DNA with electricity Step 1: DNA is isolated and cut with restriction enzymes Makes different sized pieces of DNA (RFLP) Step 2: Polymerase Chain Reaction (PCR) Makes many copies of the chopped up DNA Southern Blot/Electrophoresis

  19. Southern Blot/Electrophoresis • Step 3 • Put DNA in gel • Run electricity • Long pieces of DNA stay toward the negative side • Short pieces of DNA move closer to the positive side • Get bands of different size DNA

  20. Interpret Southern Blot • If the lines match up, that is the same person • If the lines are really similar, they are related but not same person

  21. DNA: Cont’d • Chromosomes- DNA packed tightly together • Unravel chromosome, 2 meters DNA per cell, or 2 x 1010 km per individual • Earth circumference: 4 x 104 km • Distance to sun: 1.5 x 108 km • You have 23 pairs of chromosomes, 46 TOTAL chromosomes • One pair determines gender • XX = female • XY= male • Individuals possess 2 copies of each chromosome • 1 from mom • 1 from dad

  22. DNA: Cont’d Xome 4 • Chromosomal map- can find particular gene location on a chromosome (like using map to find location in U.S.) • If looking for particular gene, look at pattern to see how long it is • Loci: Area on chromosome • Locus on xome is chromosomal address • Example: D13S1358 • D= DNA • 13= xome # • S= branch of xome • 1358= location

  23. CODIS • CODIS- Combined DNA Index System • Catalogue of various body fluids (blood, saliva, semen, etc.) • Body fluid from crime scene can be compared to index system to determine if there is a match

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