1. Blood

2. Use of Blood
Provides class evidence because more than one person has the same blood type
White blood cells contain DNA so it’s possible to determine if blood at a crime scene is from a suspect or a victim

3. Composition of Blood
Plasma – the straw-colored liquid portion of the blood
Red Blood Cells – function in carrying oxygen and carbon dioxide
White Blood Cells – function in the immune system; only blood cell to contain DNA
Platelets – function in clotting

4. DNA Profiling
DNA evidence has been used by the Innocence Project to help free inmates falsely convicted of crimes

5. Blood Typing
Less expensive way to analyze blood evidence than DNA analysis
This is a form of class evidence because it can only identify a group of individuals
Different proteins are present on the surface of red blood cells and these determine blood type

6. Blood Types
Type O – does not have any proteins on the surface of red blood cells (43% of people are Type O)
Type A – has protein A on the surface of red blood cells (42%)
Type B - has protein B on the surface of red blood cells (12%)
Type AB – has both protein A & B on the surface of red blood cells (3%)

7. Rh Factor Another protein on the surface of red blood cells
85% of people have this protein (Rh+)
15% of people do not have this protein (Rh-)

8. Blood Typing Tests There are three items to test for:
A protein
B protein
Rh protein
There are many other blood proteins (hundreds) that can further help to identify an individual

9. Probability and Blood Types
We can calculate the percentage of the population who has a particular type of blood
Ex: What percentage of people have A+ blood?

10. Type A – 42%
Positive – 85%
Convert these to decimals, multiply them, then multiply by 100 to get a percentage
0.42 x 0.85 = x 100 = 35.7%
36 out of 100 people should be A+

11. Universal Donor – O negative
Can be given to anyone because it doesn’t have any proteins on the surface of it’s red blood cells
Universal Recipient – AB positive
Can get any blood because it has all proteins on the surface of it’s red blood cells