Serology

The study of body fluids

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

Quiz…

What is the most common body fluid left behind at a crime scene? Blood

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

Genetics continued…

Genotype- specific genetic make-up

Phenotype- observed characteristics

Punnet Square- diagram of genetic possibilities