Blood Classification • Blood factors are controlled genetically • >100 known blood factors • More than 15 classification systems e.g. A-B-O system.
What is blood? 1. Plasma – fluid portion, mainly water. 2. Cells - red blood cells (erythrocytes) - white blood cells (leukocytes) - platelets (Note: serum is the yellowish fluid after blood clots.)
What about blood types? • Antigens : impart the blood type characteristics on RBC’s. • A-B-O system: presence or absence of A or B antigens. • Rh system: presence or absence of D antigen.
Antibodies: proteins found in the serum. • Antibodies have two reactive sites allowing them to attach to two of the same antigens simultaneously agglutination
What is Serology? Any test involving antibody-antigen reactions e.g. A-B-O agglutination reaction, many immunoassay techniques.
Immunoassay Techniques. • Antibody-antigen reactions used to detect drugs in urine and blood. - EMIT tests such as THC kits, methadone test kits. • Antibodies capable of reacting with the drugs are produced in animals.
Characterization of Blood 1. Is it blood? 2. What species? 3. If human, can it be associated with a particular individual?
Preliminary Tests 1. Is it blood? • Benzidine color test or Kastle-Meyer color test. • Luminol test • Microcrystalline tests 2. What species? • Precipitin test
Individualizingblood evidence. Blood is class evidence! ….further testing may “individualize” this evidence to one person. Polymorphic Proteins • Enzymes (proteins) that exist in different forms. • Enzymes separated into individual components called isoenzymes, each having the same (or similar) enzyme activity.
Phosphoglucomutase (PGM) • Common Isoenzymes of PGM PGM 1 (58%), PGM 2-1 (36%), PGM 2 (6%). Variation within the population helps decrease the number of “likely suspects”.
Bloodstain Patterns. Must consider: • Surface Texture • Direction of Travel • Impact angle of blood • Origin of spatter.
Surface Texture Surface texture can change the appearance of the spatter and must be taken into consideration. Smooth hard surface Wood or concrete
Point of Convergence By drawing a line through the long axis of a group of bloodstains and determining where they cross each other the point of convergence can be determined.
Point of Origin • Construction of a 3-D model
Angle of Impact • By measuring the length and width of the blood stain, the angle and direction of impact can be determined. sin A = width of bloodstain length of bloodstain
Velocity of Impact • Low • Medium • High
Low Velocity • - free falling drops of blood. • - sometimes called “passive” spatter.
Medium Velocity • Produced when one object strikes another • - blunt (fist,club) or sharp (knife) trauma.
High Velocity - gunshot, power tools, explosion.
Impact Spatter • Back and forward spatter (arrow shows direction of projectile)
Heredity: it’s in the genes! • Gene is the basic unit of hereditary. • Genes are positioned on chromosomes. - 46 chromosomes (23 pairs) “Sex chromosomes”: X and Y XX female XY male
Origin of different characteristics • Genes that influence a given characteristic (PHENOTYPE) are grouped together in allelles. • Every characteristic requires a pair of genes (two genes). This is the GENOTYPE. both the same - homozygous different - heterozygous
Paternity Testing • Disputed paternity can be resolved by determining blood type. Punnet Square: A A A AA AA B AB AB