1. Forensic Serology
Chapter 12

2. 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

3. 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

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

5. 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

6. 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

7. Chromosome

8. 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

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

10. 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

11. 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

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

13. Type A Possessed by people with genotype A is dominant to OAA AO
A is dominant to O
Have A antigens

14. Type B Possessed by people with genotype B is dominant to OBB BO
B is dominant to O
Have B antigens

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

16. 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

17. 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)

18. 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

19. 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

20. 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

21. Donors

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

23. 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)

24. 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?

25. 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

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

27. 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

28. Luminol Test

29. 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

30. Precipitin Test

31. 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

32. 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

33. 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