1. Blood Type Evidence
Monday, October 9, 2017

2. Target 2-1
I can include and exclude suspects by interpreting blood type evidence.

3. What is Blood?
Blood is used to transport waste and nutrients in our bodies.
All human blood contains three types of blood cells floating in a clear liquid called plasma.

4. Blood Cells Platelets: clot blood to prevent over-bleeding
White blood cells: defend the body from bacteria, viruses, and bad cells (such as cancer)
Red blood cells: contain hemoglobin – used to transport oxygen from the lungs to the rest of the body

5. Antigens and Antibodies
Antigens and antibodies attach themselves to red blood cells.
ANTIGEN: protein that triggers an immune response (the body will defend against it)
ANTIBODY: protein that defends the body from antigens
There are 3 types of antigens that can occur in human blood: A, B, Rh
Each antigen has a specific antibody that fights it: anti-A, anti-B, anti-Rh

6. Blood Type
Blood Type is a way of classifying which antigens and antibodies are present in a sample of human blood
Blood MUST contain either antigens or antibodies for A, B, and Rh
If my blood contains antigen A, it will NOT contain antibody anti-A

7. Blood Type Type Antigens Antibodies A+ A, Rh anti-B A- A
anti-B, anti-Rh B+
B, Rh
anti-A B- B
anti-A, anti-Rh
AB+
A, B, Rh
None
AB-
A, B
anti-Rh O+ Rh
anti-A, anti-B O-
anti-A, anti-B, anti-Rh

8. Blood Type as Evidence
If blood is found at a crime scene, we can test it to determine the blood type
We can test for blood type even on old or dried blood, when we cannot get DNA
Since many people have each blood type, we can only include or exclude suspect matches
Include: The suspect may have left the blood
Exclude: The suspect could not have left the blood (although he/she could still be guilty!)
Even if we include a suspect, we cannot prove the suspect committed the crime

9. Testing for Blood Type
We separate a sample into 3 smaller samples and test with antibody serums
If the sample “clumps” with the antibody, we know that antigen is present
Ex) A clump with anti-B serum indicates B antigen
If the sample does not clump, we know that antigen is not present