Blood Use of Blood n Provides class evidence

Blood

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

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

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

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

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

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

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

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

n Type A – 42% n Positive – 85% n Convert these to decimals, multiply them, then multiply by 100 to get a percentage n 0. 42 x 0. 85 = 0. 357 x 100 = 35. 7% n 36 out of 100 people should be A+

n 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 n Universal Recipient – AB positive § Can get any blood because it has all proteins on the surface of it’s red blood cells