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Forensic Serology

Forensic Serology

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Forensic Serology

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  1. Honors Forensic Science Forensic Serology

  2. i. Blood is most common bodily fluid left a crime scene Ii. Often most useful body fluid left a crime scene I. General

  3. i. 1901 – Karl Landsteiner – discovered method to type blood; won Nobel Prize Ii. 1937 – Rh factor was discovered II. History

  4. i. Composed of a mixture of cells, enzymes, proteins, and inorganic substances Ii. Fluid portion of blood = plasma. Comprises 55% of blood content III. Blood

  5. 1. erythrocytes – red blood cells 2. leukocytes – white blood cells 3. platelets – tiny cells involved in blood clotting iii. Suspended in plasma are

  6. Iv. Blood clots when protein (fibrin) traps and enmeshes RBCs V. If remove clotted material would have serum left

  7. 1. more than 15 systems identified 2. ABO and Rh most important 3. Type A – has A antigens 4. Type B – has B antigens 5. Type AB – has both 6. Type O – has neither vi. On RBC surface are antigens

  8. 1. serum contains proteins (antibodies) that destroy specific antigen 2. add Anti-A serum to Type A blood and agglutination vii. Method to type blood

  9. 1. O – 43% • 2. A – 42% • 3. B – 12% • 4. AB – 3% • 5. Rh • 1. positive – 85% • 2. negative – 15% viii. People in US with different blood types

  10. i. Questions to ask • 1. is it blood? • 2. what species? • 3. if human, how closely can it be associated to a particular individual? IV. Forensic Characterization of blood

  11. 1. must have enough blood and must be in good condition for testing 2. some chemicals damage blood to the point that DNA typing then cannot be performed 3. putrefacation can also degrade samples 4. dried samples may not have decayed as much ii. Is it blood?

  12. 1. Presumptive Tests – indicate a likelihood that blood is present but don’t establish that as a fact • 1. Benzidine color test – turns pink • 2. Kastle-meyer Color Test – turns pink • i. Both Kastle-Meyer and Benzidine are based on the observation that blood hemoglobin possesses perioxidase-like activity 5. Tests

  13. 3. Hemastix – useful in field; turn green 4. Luminal – results in production of light 5. very sensitive 6. Does not interfere with DNA

  14. - are certain about blood presence • 1. More expensive and time consuming • 2. Also called Microcrystalline tests – as characteristic crystals formed when chemicals are added • 3. Teichmann and Takayama tests 2. Confirmatory tests

  15. 1. Precipitin Test • 1. Precipitin = an antibody that reacts with its corresponding antigen to form a precipitate • 2. If inject animal with human blood, antibodies form that react with human blood to neutralize it • 3. Isolate these antibodies = human anti-serum iii. What Species?

  16. 1. Gel diffusion – extracted bloodstain and human anti-serum are placed in gel; if human, line will form 2. Electrophoretic method – uses current 2. Various methods to perform tests

  17. i. Very sensitive Ii. Requires small amount of blood Iii. Can use old, dried blood Iv. Can use blood diluted by washing in water

  18. 1. ABO Types (whole blood) • 2. Typing Dried Stains – absorption – elution • 1. No RBCs present because have degraded. Can still get antigens out. • 2. Treatment with anti-serum; antibody binds to its specific antigen • 3. Excess antibodies are removed by washing iv. Can blood be associated to a particular individual?

  19. 4. Antibodies and antigens are eluted or freed from one another by heating the stained material 5. Add known red blood cells and agglutination occurs if antigens present on the added blood cells were originally on stained material as well

  20. 6. Is a sensitive test 7. 11 year old blood stains have been successfully typed

  21. 1. 80% of individuals 2. = an individual who secretes his or her blood-type antigen(s) in body fluids (semen, saliva, etc) 3. Secretors

  22. 1. different forms used to discriminate among bloodstains 2. Enzyme = type of protein that acts as a catalyst for certain specific reactions 4. Blood enzymes and proteins

  23. 3. Many are polymorphic and can be separated into iso-enzymes (multiple molecular forms of an enzyme, each having same or similar enzyme activities) 4. Frequency of blood enzymes and proteins in blood and populations

  24. i. Transmission of our Traits • 1. all antigens, polymorphic enzymes and proteins are genetically controlled traits • 2. transmission of hereditary material is through our genes which are positioned on our chromosomes • 3. alternative forms of genes are called alleles V. Principles of Heredity

  25. 4. Reproductive cells (egg and sperm) contain half of the chromosomes/genes of the parent. During fertilization, the new zygote receives one half of its chromosomes/genes from the mother and one half from the father.

  26. 5. If the two genes are alike = homozygous 6. If the two genes are different = heterozygous 7. The genes present in an individual = genotype 8. The physical manifestation of the genetic trait = phenotype

  27. 9. Use of principles of heredity is useful in determining ABO blood types in children and parents 10. Punnet Squares can be used to determine

  28. 11. Example: Male parent is Type O (phenotype) and therefore has OO as his genotype and the female parent is Type AB (phenotype) and therefoere has AB as her genotype. Construct a Punnet Square to determine possible genotypes and phenotypes of their offspring.

  29. 12. 50% are likely to be Type A (AO) and 50% Type B (BO) 13. Bottom line, no blood group gene can appear in a child unless it is present in at least one of the parents. 14. Useful in paternity testing.

  30. i. Information of bloodstain patterns provide includes: • 1. origin of the bloodstains • 2. the type of instrument that caused the bloodstain • 3. the direction from which an object struck the victim vi. Stain patterns of blood

  31. 4. the relative positions of the victim, assailant(s), and bystanders 5. the locations and movements of the victim and assailant during the attack 6. the number of blows or gunshots the victim received 7. the truthfulness of any suspects and witnesses

  32. 1. surface texture – in general, the harder and less porous the surface, the less spatter results ii. Circumstances that affect stain patterns

  33. 2. The direction of travel of blood striking an object may be discerned by the stain’s shape. The pointed end always faces its direction of travel.

  34. 3. the impact angle of blood on a flat surface can be determined by measuring the degree of circular distortion of the stain. • Example – right angle = nearly circular. As angle increases or decreases it becomes more elongated.

  35. 4. Origin of spatter: Draw straight lines through long axis of several individual bloodstains. The intersection or point of convergence of the lines represent the point from which blood emanated.

  36. 5. Edges – can indicate velocity of impact and blood droplet. Higher velocity impacts produce drops with more ragged edges.

  37. 1. Low velocity spatters – blood moving less than 5 ft per second • 1. A droplet that forms slowly, as in a dripping wound, is generally larger • 2. Arterial bleeding is also considered low velocity • 3. Cast-off blood or blood that is flung from an object because of centrifugal force iii. Classifying projected spatters

  38. 2. Medium velocity spatters – moving between 5 and 100 ft per second • 1. smaller droplets are more often produced during active situations • 2. come from impact with blunt or sharp objects • 3. blood mixed with exhaled air creates a fine spray and a mist spatter pattern