Forensic Serology Chapter 12

Topics this Chapter: Blood typing DNA profiling (later chapter) Class evidence (presumptive) DNA profiling (later chapter) Individual evidence (confirmatory) Blood Spatter Helps reconstruct crime scene

The Nature of Blood Blood – made up of cells, enzymes, proteins, inorganic substances Plasma – fluid portion of unclotted blood Dissolved proteins, antibodies, hormones, clotting factors, nutrients (glucose, amino acids, salts, minerals) Comprises 55% of blood Solid portion – blood cells Comprises 45% of blood

Types of Blood Cells Red blood cells – erythrocytes White blood cells – leukocytes Platelets – clotting factor

Erythrocytes Possess surface proteins called antigens Antigens impart blood type characteristics A protein = Type A B protein = Type B AB proteins = Type AB No proteins = Type O

Genetics Chromosomes – threadlike bodies that appear in nucleus of every cell; made up of DNA Human body cells contain 46 chromosomes Human reproductive cells contain only 23 chromosomes Genes – segments of DNA on chromosomes that are the basic unit of heredity Control the development of specific characteristics Allele – alternative forms of genes located at the same point on a particular chromosome A and B are possible alleles for the blood type gene Locus – physical location of a gene on a chromosome

Chromosome

Genotype vs Phenotype Homozygous – two identical alleles AA for blood type Heterozygous – two different alleles AB for blood type Genotype – combination of alleles present in the DNA (chromosomes) AA, BB, AO, etc Phenotype – physical manifestation of a genetic trait Shape, color, blood type

How do we inherit traits? Mother’s genotype vs. father’s genotype Punnet Square Dominant traits Recessive traits

Blood typing History 1901 – Karl Landsteiner Noticed a huge number of deaths in blood transfusions Developed the A-B-O system of classification Still most important system for matching a donor and recipient for transfusion

Blood Typing Three types (alleles) of blood type gene A, B, O Code for the antigen present on the surface of red blood cells 6 possible combinations (genotypes) AA, BB, OO, AB, AO, and BO Genotype determines blood type Rh factor – D antigen D antigen present: Rh positive D antigen absent: Rh negative

Type O Blood Possessed by people whose genotype is OO both parents passed on the O gene Have no antigens

Type A Possessed by people with genotype A is dominant to O AA AO A is dominant to O Have A antigens

Type B Possessed by people with genotype B is dominant to O BB BO B is dominant to O Have B antigens

Type AB Possessed by people with genotype Have both A and B antigens A & B are co-dominant Have both A and B antigens

Antigens and Antibodies Antigen - A substance on the surface of a cell that stimulates body to produce antibodies against it Over 15 different types on red blood cells A-B-O and Rh are most important Antibodies – a protein that destroys or inactivates a specific antigen Antibodies develop about 2-8 months after birth Found in blood serum Responsible for ensuring that the only blood cells that can survive in a person are cells of the correct blood type

Antigens and Antibodies Type A blood has A antigens Produces B antibodies (called Anti-B) Type B blood has B antigens Produces A antibodies (called Anti-A) Type AB blood has A & B antigens Produces no antibodies Type O blood has no antigens Produces A & B antibodies (Anti-A and Anti-B)

Antigen-Antibody Response Foreign invader is recognized by the immune system, and the immune system launches an attack against the invader Immune system “recognizes” invader as foreign by the foreign antigens on the surface of the cell Viruses, bacteria, red blood cells from different blood type have foreign antigens

Clotting - Agglutination An antigen and an antibody of the same type react to clump RBC (called agglutination) So, if antigen A is exposed to anti-A, agglutination will occur

Blood Typing Blood typing is done by reacting whole blood with antibody A and antibody B Antibody A will cause A and AB blood to clot Antibody B will cause B and AB blood to clot Type O blood contains no antigens so will not clot

Donors

Probability Typical Distribution in U.S. O: 43% A: 42% B: 12% AB: 3%

Additional Blood Proteins M and N proteins (MM,MN,NN) Phosphoglucomutase (PGM) Adenylate kinase (AK) Adenosine deaminase (ADA) Esterase D (EsD) Glucose-6-phosphate dehydrogenase (G-6-PD) Polymorphic Proteins: Group-specific Components (Gc) and haptoglobins (Hp)

Forensic Characterizations of Bloodstains Is it blood? From what species did the blood originate? (Usually human or animal) If the blood is human, how closely can it be associated to a particular individual?

Is it blood? Benzidine color test– discontinued Contains known carcinogen Kastle-Meyer color test – took place of benzidine color test Bloodstain, phenolphthalein reagent and hydrogen peroxide mixed: hemoglobin will form a deep pink color

Is it blood? Hemastix® - moistened with distilled water and placed in contact with bloodstain Green color is positive for blood

Is it blood? Luminol test – produces light rather than color Large areas covered quickly Objects must be in darkened area while being viewed for luminescence Extremely sensitive Can detect blood diluted up to 300,000 times Will not interfere with further DNA testing Takayama and Teichmann tests Microcrystalline tests for blood Specific chemicals added to form crystals with hemoglobin

Luminol Test

Human or animal blood? Precipitin Test determines whether blood is human or not Like immunoassay for drugs except for human blood Uses antiserums of known original to react with blood sample Precipitin band is formed if a match Can be used on bloodstains 10 to 15 yrs old or older

Precipitin Test

Human or animal blood? Gel Diffusion Electrophoretic method antigens and antibodies will move toward one another on an agar-coated plate Electrophoretic method Electrical potential is applied to the gel

Can we narrow it down to a particular individual? Enzymes – another substance in blood used to try to individualize bloodstains This is more historical in use – before 1990’s DNA is primarily used now

Paternity Testing Encountered in civil courts, usually not criminal courts The more blood group systems tested, the better the chances of excluding an innocent male Routine testing involves other blood groups than A-B-O HLA (human luekocyte antigen) White blood cells Chances better than 90% suspect is father if he cannot be excluded after this test