Blood Type Evidence Monday, October 9, 2017

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

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.

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

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

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

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

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

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