Serology The Bodily Fluids. Your identity shows up in more places than your driver’s license…
Serology The study of body fluids. Serology-Definition The study of antigen/antibody reaction The...
Transcript of Serology The study of body fluids. Serology-Definition The study of antigen/antibody reaction The...
Serology-Definition
The study of antigen/antibody reaction
The study of biological fluids Blood, sweat, tears,
saliva, semen, etc.
But, I was not even at the crime scene…
If you leave behind a body fluid sample, it proves your presence at the scene.
Serological evidence has more weight than fingerprinting.
Often used in cases of paternity and ancestry
Blood Info
Plasma Liquid portion of whole blood
Contains proteins, enzymes, clotting factors, electrolytes, and 3 types of cells
Leukocytes – white blood cells Erythrocytes – red blood cells Platelets – cells involved in clotting
Blood Serum
When blood clots and the clotted material is removed, a yellowish liquid remains Yellowish fluid is serum
Serum contains the majority of proteins and enzymes
Serum contains the antibodies
Important components
2 components of blood are very important to forensic scientists RBC’s and serum
With these two components, a serologist can determine blood type from any sample or stain
With more than 100 blood factors known, it is theoretically impossible for two people other than identical twins to have the same combination of blood factors.
Blood Types
Dr. Karl Landsteiner – responsible for ABO blood typing system, allowed for safe matching of blood donor to recipient
Knowing the blood type helps to narrow the suspect list
Blood Types
Determined by antigens present on cells A – a antigen B – b antigen D antigen – Rh factor
Found in most people, responsible for violent antigenic reactions
Can be harmful if Rh negative meets Rh positive during mating
Antigens
A substance, usually a protein, that stimulates the body to produce antibodies to fight an intrusion
There are more than 15 known blood antigens
Antibody
For every antigen, there is an antibody An antibody is highly specific, this means
that only recognizes and interacts with its specific antigen
The combination of antigen and antibody forms an antigen-antibody complex – the basis for blood typing
How do you type blood?
Use antiserum to test for agglutination (clumping) Anti A – will make type A clump Anti B – will make type B clump Type O will not clump with either Anti A or Anti B Anti Rh – will make Rh+ clump
Some Blood Statistics
43% of Americans have type O
42% of Americans have type A
12% of Americans have type B
3% of Americans have type AB
Who is the Universal Donor?
A- receive blood from A & O Give to A & AB
B- receive blood from B & O Give to B & AB
AB- receive blood from A, B, AB, O Give to AB AB is the Universal Receiver
O- receive blood from O Gives to A, B, AB, and O O is the Universal Donor
What to do with crime scene blood…
Type each blood sample separately
At scenes with multiple victims, typing and antigen-antibody complexes help reconstruct crime scene
How much blood is needed?
Modern technology allows us to test minute amounts of blood, but the sample does not hold substantial weight like a large sample
Chemical reactions from the antigens and DNA fingerprinting could degrade small samples
Putrefaction- the decay of cells due to bacterial activity in old samples
What is done with blood evidence?
Typing often tells the story of how and when things happened Time of bloodstain is difficult to determine
Exclude suspects Extract DNA
Secretors
A secretor is a person who provide blood typing requirements in all body fluids. Examples: saliva, semen, gastric juices, etc.
Do not confuse blood typing with DNA typing – you can obtain DNA from all body fluids of every person
DNA TYPING AND BLOOD TYPING ARE NOT THE SAME THING
How do you know if a stain is blood?
Presumptive Testing Kastle-Meyer Color Test Hemastix Luminol
Specific Testing Microcrystalline Test Precipitin Test
Kastle-Meyer Color Test
Blood stain + phenolphthalein + hydrogen peroxide = deep pink color
Being a color test, it is only considered presumptive
False Positives: Potatoes and Horseradish
Hemastix Test
Hemastix strip moistened with distilled water + blood sample = green color
Also a color test and thus is presumptive
Luminol Test
Luminol + blood + dark = light
Must be viewed in the dark
Extremely sensitive Can detect bloodstains
diluted up to 10,000,000 times
Does not interfere with DNA testing
Microcrystalline Test
Confirmative test 2 popular versions
Takayama Teichmann
Both versions depend on chemical additions to the blood
Test is susceptible to interferences of contamination
Precipitin Test
Human antiserum added to blood sample
If agglutination occurs, then the sample is human blood
2 methods: capillary tube, gel diffusion
Can be used on samples up to 10-15 yrs old
Has produced positive test on 4-5 thousand year old mummies
Not human blood?
You can still use the precipitin test with other antiserums
Using a species specific antiserum, a serologist can determine the source of the blood
DNA Fingerprinting/Typing
Testing for paternity You inherit your blood
type from your parents Paternity confirmation
plays a role in child support, custody, visitation
Also has role in crimes that involve kidnapping, insurance fraud, and inheritance
Heredity
Transmission of hereditary material is done through genes
Genes are found on chromosomes Humans have 46, 23 from mother, 23 from
father, found in pairs resulting in 23 chromosomes in normal cells
XX – female XY – male Females always donate X, Males donate
either X or Y
Genetics
Locus- Position of a gene on a chromosome Alleles- alternative forms of genes Homozygous- AA, aa Heterozygous- Aa Dominant- always represented Recessive- not seen if dominant is present Codominant- not seen in full effect