Honors Forensic Science

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

 i – Karl Landsteiner – discovered method to type blood; won Nobel Prize  Ii – Rh factor was discovered

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

 1. erythrocytes – red blood cells  2. leukocytes – white blood cells  3. platelets – tiny cells involved in blood clotting

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

 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

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

 1. O – 43%  2. A – 42%  3. B – 12%  4. AB – 3%  5. Rh  1. positive – 85%  2. negative – 15%

 i. Questions to ask  1. is it blood?  2. what species?  3. if human, how closely can it be associated to a particular individual?

 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

 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

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

 - 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

 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

 1. Gel diffusion – extracted bloodstain and human anti-serum are placed in gel; if human, line will form  2. Electrophoretic method – uses current

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

 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

 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

 6. Is a sensitive test  year old blood stains have been successfully typed

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

 1. different forms used to discriminate among bloodstains  2. Enzyme = type of protein that acts as a catalyst for certain specific reactions

 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

 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

 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.

 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

 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

 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.

 % 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.

 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

 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

 1. surface texture – in general, the harder and less porous the surface, the less spatter results

 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.

 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.

 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.

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

 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

 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

 3. High velocity spatters – faster than 100 ft per second  1. aerosol spray indicates wound produced by a powerful force, such as a gunshot or explosion

 2. Bloodstain associated with entrance wound = blowback or back spatter, meaning droplets travel in a direction opposite to the path of the bullet  1. can be found on the shooter or weapon

 3. bloodstain found near exit wound = forward spatter, it follows the direction of the bullet

 i. Semen  1. normal male releases 2.5 to 6 ml of seminal fluid during ejaculation  2. each ml contains 100 million or more sperm

 3. Forensic Characterization of semen is 2 step process  1. Stain must be located  i. Sometimes is clearly visible  Ii. Other times difficult to find, can use test to determine presence of seminal fluid  2. Sperm must be identified

 1. Acid Phosphatase Color Test  1. Acid phosphatase = enzyme produced by seminal vesicles  2. use of reagent on materials results in fluorescent areas under UV light in presence of semen  3. May produce a false positive

 1. Microscopic Examination – examination for intact sperm or sperm head  1. Problem – if individual had vasectomy, no sperm may be present

 2. Prostate-specific antigen (PSA)  1. Present even in individuals who have had a vasectomy  2. Is an antigen-antibody reaction

 6. Secretor Status  1. Can determine blood types from semen in % of individuals

 1. may be recovered from everything from stamps to food to bite marks  2. may reveal ABO antigens and blood types in secretors and sometimes can yield enough DNA for profiling

 3. Testing for saliva involves testing for alpha- amylase enzyme found in saliva – is only a presumptive test  4. No confirmatory tests for saliva