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Who’s blood is it?. 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

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Who’s blood is it?


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 Sample

be used for

identification?



Who’s blood is it?

Black Blond Red

hair hair hair

X

X

X


Blood evidence
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 mighthave happened.


  • 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


Microscopic views

Fish Blood

Bird Blood

Horse Blood

Cat Blood

Frog Blood

Human Blood

Snake Blood

Dog Blood

MicroscopicViews


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


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

IMMUNE SYSTEM

Red Blood Cell

CHEMICAL MARKERS

ANTIBODIES


Blood types
BLOOD TYPES

  • Blood can be classified by either:

  • 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
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 A

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

Blood Group B

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

Blood Group AB

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

Blood Group O

If 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

B Rh+

B Rh-

AB Rh+

AB Rh-

O Rh+

O Rh-

A Rh+

A RH-


Blood Typing

  • 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.

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

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

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

  • 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.

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

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



Crime Lab: Blood Analysis Unit

Name of Examiner: _____________

Blood Typing: Results for 4Suspect’s Blood Types

EVIDENCE BLOOD: TYPE O+

Summary of findings:


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