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Forensic Serology. Identification Using Blood Groups. This presentation contains graphic pictures. Forensic Serology. Serology – term used to describe a broad range of laboratory tests using reactions of blood serum and body fluid.

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Forensic Serology

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Forensic serology l.jpg

Forensic Serology

Identification Using Blood Groups

This presentation contains graphic pictures.


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Forensic Serology

Serology – term used to describe a broad range of laboratory tests using reactions of blood serum and body fluid

  • The serology section of a forensic laboratory may deal with any or all of the following:

  • blood typing

  • characterization of unknown blood

  • stain patterns for crime reconstruction

  • paternity testing

  • semen identification in rape cases

  • DNA techniques used for identification


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The Composition of Blood

Blood is a mixture of many components:

cellsinorganic substances (salts)

enzymeswater

proteins

55 % of blood content is plasma – mostly water and substances dissolved in it

Most of the solid materials (by weight) are cells

red blood cells, RBCs (erythrocytes)

white blood cells (leukocytes)


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Forensic Characterization of Bloodstains

Three questions that must be answered by the forensic investigator:

1) Is it blood?

Benzidine Test

Kastle-Meyer Test

Hemastix (o-tolidine, TMB)

Luminol Test

2) Is it human blood?

Precipitin Test

3) Can it be associated with an individual?


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Luminol

  • Red blood cells contain hemoglobin (Hb) – the protein responsible for transporting oxygen

  • Each Hb contains four iron (Fe) containing hemes

Heme structure


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Luminol

  • Red blood cells contain hemoglobin (Hb) – the protein responsible for transporting oxygen

  • Each Hb contains four iron (Fe) containing hemes

Heme structure


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Forensic Characterization of Bloodstains

Three questions that must be answers by forensic investigator:

1) Is it blood?

Benzidine Test

Kastle-Meyer Test

Hemastix (o-tolidine, TMB)

Luminol Test

Enzymatic Tests

2) Is it human blood?

Precipitin Test

3) Can it be associated with an individual?


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Precipitin Test


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Blood Antigens

On the surface of red blood cells are chemical structures (proteins) calledantigens

The presence of antigens allow a living system to recognize foreign biological substances

Antigens also impart specific characteristics to the red blood cells. These characteristics can be partly used to identify individuals

Human red blood cells have more than 15 different antigen types that have been discovered


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Blood Typing

Blood typing involves determination of the antigens present on an individual’s RBCs

The two most common blood typing systems used are the A-B-O method and the Rh method

type A blood – contain “A” antigen on RBCs

type B blood – contain “B” antigen on RBCs

type AB blood – contains both A and B antigens

type O blood – contain no A or B antigens

Rh+ blood – contain Rh antigen

Rh- blood – no Rh antigen


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Blood Typing

Blood also contains antibodies –proteins that recognize and bind to certain, specific antigens

Blood TypeAntigens on RBCAntibodies

A A anti-B

B B anti-A

AB AB none

O none both A & B


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Blood Typing

When blood containing a specific antigen is mixed with blood containing the corresponding antibodies, the blood clots

The clots can then be removed by the host system


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Blood Typing

Human serum containing specific antibodies can be purchased

Separately mix a drop of unknown blood sample with drop of each anti-serum

Reaction between blood and anti-serum

No reaction between blood and anti-serum


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Blood Typing Example

A sample of unknown blood is mixed with three anti-sera samples:

Tube 1 (Anti-A): No reaction

Tube 2 (Anti B): No reaction

Tube 3 (Anti Rh): Cloudy reaction

In terms of the A-B-O and Rh systems, what type blood is the sample?

The ABO antigens are not confined to RBC; 80% of Americans are secretors, found on other cells


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Blood Typing Example

A sample of unknown blood is mixed with three anti-sera samples:

Tube 1 (Anti-A): No reaction

Tube 2 (Anti B): No reaction

Tube 3 (Anti Rh): Cloudy reaction

In terms of the A-B-O and Rh systems, what type blood is the sample?

The ABO antigens are not confined to RBC; 80% of Americans are secretors, same antigens found on other cells

O positive


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Blood Splatter Analysis

Categories of Bloodstains:

Passive (dripping)

Transfer (smearing)

Projected

Projected Bloodstains occur in shootings, trauma from blunt weapons, hacking, or slashing attacks.


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Projected Bloodstain Analysis

Two Important Determinations:

a. direction of splatter

b. angle of impact with surface

sin  = (width drop / length drop)


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Forensic Characterization of Semen

  • Many crimes involve sexual misconduct

  • Normal males, upon ejaculation, release seminal fluid. This fluid is a mixture of components:

  • water

  • spermatozoa

  • enzymes

  • inorganic salts

  • Semen at a crime scene (clothing, bed sheets, carpet, cushions) can be located and identified by three common methods:

  • microscope examination to find sperm

  • acid phosphatase test

  • p30 (also called prostrate specific antigen) immunoassay test


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Forensic Characterization of Saliva

Saliva is a mixture of many components:

99% water

Mucin (protein helps in swallowing)

Amylase (enzyme to help digest carbohydrates)

Cheek cells (good for DNA)

Adults produce 1.0-1.5 liters of saliva/day and it is not uncommon at crime scenes (especially involving bite marks).

A simple test for saliva involves mixing starch, iodine, and a sample of the presumed saliva together. Starch and iodine are a deep blue color when mixed together. The amylase breaks down starch, however, and the color fades (takes about 15 mins @ 37 oC).


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