1. And how we can test for it
Blood Types
And how we can test for it

2. Blood Types A B AB O (42%) (12%) (3%) (43%) CLASS
What are the blood types?
A B AB O
(42%) (12%) (3%) (43%)
All of these blood types can also be negative or positive
Your blood type is determined by heredity
So, what type of evidence would a blood type be?
CLASS

3. Blood Types
What makes one blood type different from another is the antigens on the surface of the red blood cells.
Antigens are proteins on the surface of a cell, but they have different shapes
These antigens can be recognized by specific antibodies (that would mark them for destruction).
So, if you have type A blood, you will have B-antibodies so your body will destroy a foreign blood type

4. Blood Types

5. Rh Factor
Whether or not a blood type is negative or positive is determined by presence of a different antigen (D- antigen)
If you have the antigen your blood type is considered positive
If you don’t have the antigen your blood type is negative, but you will have the D-antibodies
This means people with negative blood cannot receive blood from people with positive blood

6. Clumping
When red blood cells with a specific antigen (ex: A) are mixed with blood containing the antibody for that antigens (ex: B) then the antibodies attach to the blood cells and cause them to clump together.
This can lead to death during a transfusion if a type of blood is given that is not compatible.
The clumping together of the antigens and antibodies is called agglutination

7. Determining Blood Type
We test blood for a blood type first because it is quick, cheap, and easy.
Since it is a form of class evidence it will not prove guilt, but simply exclude or include suspects.
All we have to do to test blood types is mix unknown blood with the different antibodies and look for agglutination.
When we get a positive reaction or clumping, that is our blood type.

8. Other Blood Proteins
Other proteins on the surface of blood cells have now been identified as well and can be used for identification:
M and N proteins
Phosphoglucomutase (PGM)
Adenylate kinase (AK)
Adenosine deaminase (ADA)
Esterase D (EsD)
Glocose-6-phosphate dehydrogenase (G-6-PD)
Polymorphic proteins: Group specific Components (Gc) and haptoglobins (Hp)
Type
Percentages MM
30% MN
48% NN
22%

9. Blood Type Probability
From what we know about percentages of given blood types in the population we can determine probability that the unknown blood at a crime scene matches a suspect . . .
If we analyze blood at a crime scene and find out it is O- and has both M and N proteins, what percent of the population will that class include?
0.07 x 0.48 = = 3.36%
What if we then find out there are also Hp (14%) and PGM (6%) proteins as well?
0.07 x 0.48 x 0.14 x 0.06 = = 0.28%