Who’s blood is it?

Forensic Science

T. Trimpe 2006 http://sciencespot.net/

Blood Evidence• Blood samples – Can be analyzed to determine blood

type and DNA, which can be matched to possible suspects.

• Blood droplets – Can be analyzed to give clues to the location of a crime, movement of a victim, and type of weapon.

• Blood spatter – Can be analyzed to determine patterns that give investigators clues to how a crime might have happened.

What makes up our blood?• RED BLOOD CELLS (Erythrocytes) – The most abundant

cells in our blood; they are produced in the bone marrow and contain a protein called hemoglobin that carries oxygen to our cells.

• WHITE BLOOD CELLS (Leukocytes) – They are part of the immune system and destroy infectious agents called pathogens.

• PLASMA – This is the yellowish liquid portion of blood that contains electrolytes, nutrients and vitamins, hormones, clotting factors, and proteins such as antibodies to fight infection.

• PLATELETS (Thrombocytes) – The clotting factors that are carried in the plasma; they clot together in a process called coagulation to seal a wound and prevent a loss of blood.

Blood Facts

The average adult has about FIVE liters of blood inside of their body, which makes up 7-8% of their body weight.

There are about one billion red blood cells in two to three drops of blood. For every 600 red blood cells, there are about 40 platelets and one white cell.

http://www.bloodbankofalaska.org/about_blood/index.html

Forensic Characterization of Bloodstains

Three questions to answer:1. Is it blood?

2. From what species did the blood originate?

3. If the blood is human, how closely can it be associated with a particular individual?

Kastle-Meyer Test (phenolphthalein/peroxidase test)

when a blood stain, hydrogen peroxide and phenolphthalein reagent are mixed,

the oxidation of the hemoglobin in the blood produces a deep pink color

Sensitivity: 1:10,000

(if 1 drop of blood were present in a bucket with 10,000 drops of water, the PHTH test would still turn pink)

hemoglobin - Blood contains hemoglobin (carries oxygen and makes blood red) which contains a heme group which contains an Fe which can catalyze the breakdown of hydrogen peroxide

Forensic Characterization of Bloodstains

Three questions to answer:1. Is it blood?

2. From what species did the blood originate?

3. If the blood is human, how closely can it be associated with a particular individual?

How can a

Blood Samplebe used for

identification?

1. IS IT BLOOD?Presumptive Tests

suggests but does not confirm the presence of blood; indicates that other tests should be performed

• negative result means the substance IS NOT blood

• positive result means the substance IS LIKELY blood (could be)

https://ecrimescenechemistrymiller.wikispaces.com/notes+on+serology

Kastle-Meyer Test (phenolphthalein/peroxidase test)

when a blood stain, hydrogen peroxide and phenolphthalein reagent are mixed,

the oxidation of the hemoglobin in the blood produces a deep pink color

Sensitivity: 1:10,000

(if 1 drop of blood were present in a bucket with 10,000 drops of water, the PHTH test would still turn pink)

hemoglobin - Blood contains hemoglobin (carries oxygen and makes blood red) which contains a heme group which contains an Fe which can catalyze the breakdown of hydrogen peroxide

Microscopic Views

Bird Blood

Cat Blood

Dog Blood

Fish Blood

Frog Blood

Snake BloodHuman Blood

Horse Blood

Red Blood Cell

The cell membrane of RBCs has molecules in its surface that act as identification badges so immune system can recognize it as a normal component.

Normal Foreign

CHEMICAL MARKERS

IMMUNE SYSTEM

ANTIBODIES

BLOOD TYPESBlood can be classified by either:A. Blood Type ABO identified by the type of antigen

(antigen A or antigen B)

B. Rhesus Factor another type of antigen

(Rhesus positive or Rhesus negative)

So, what is an ANTIGEN?

The differences in human blood are due to the presence or absence of certain chemicals called antigens. Individuals have different types and combinations of these chemicals.

Antigen = Antibody Generating Agent

Antigens are located on the surface of the red blood cells and the antibodies are in the blood plasma.

Blood Group AIf you belong to blood group A, you have A antigens on the surface of your red blood cells

Blood Group BIf you belong to blood group B, you have B antigens on the surface of your red blood cells

Blood Group ABIf you belong to blood group AB, you have both A and B antigens on the surface of your red blood cells

Blood Group OIf you belong to blood group O, you have no antigens on the surface of your red blood cells

Blood Group Notation

According to the above blood grouping systems you can belong to any of the

following 8 blood groups

A Rh+A RH-

B Rh+B Rh-

AB Rh+AB Rh-

O Rh+O Rh-

Blood Typing1. Place a drop of the blood sample in each well of the blood typing slide.

Replace the cap on the dropper vial. Note: Always replace cap before opening next vial to prevent contamination.

2. Add a drop of anti-A (Blue) serum to the well labeled A. Replace cap.

3. Add a drop of anti-B (Yellow) to the well labeled B. Replace cap.

4. Add a drop of anti-Rh (clear) to the well labeled Rh. Replace cap.

5. Using a different color mixing stick for each well (blue for anti-A, yellow for anti-B, white for anti-Rh), gently stir the blood sample and anti-serum drops for 30 seconds. Discard each mixing stick after use to avoid contamination.

6. Carefully examine the thin films of liquid mixture left behind. Observe for:

RESULT Appearance

(-) = NO Film remains uniform in appearance

(+) = YES Granules present

Positive result indicates the blood type

7. Record results in the data table. Answer with a YES or NO.

Type A blood