Post on 21-Dec-2015
Chapter 11; Blood
Serology; the study of bodily fluids
Separation of blood
• Living portion of blood is:• Erythrocytes (red blood cells…
RBCs)• Leukocytes (white blood cells)• Platelets
Liquid part of the blood with no cells in it is called the plasma.(Mostly water with salts, ions, proteins.)
BLOOD TRANSFUSIONS were not working!
OUTLAWED IN MOST COUNTRIES IN EARLY 1900’S
ABO Blood Typing
(Karl Landsteiner – 1901)
A classification of blood: A, B, AB, O
Rhesus monkey factor (Rh) discovered in 1940.If you have it, you’re Rh+ and if you don’t you’re Rh-
Theoretically, no two people have the same combination of blood factors and it should be possible to individualize evidence using blood, but in reality this is not the case.
Testing for every factor on RBCs in not practical, and many factors break down as blood dries and ages.
Blood is still important in forensics because testing can be done on both whole blood and dried bloodstains quickly and inexpensively.
ANTIGENS AND ANTIBODIES
Each antibody binds to a specific antigen; an
interaction similar to a lock and key.
The antibody destroysthe antigen
AGGLUTINATION
THE CLUMPING TOGETHER
OF RED BLOOD CELLS
Lattes slide
method
Uses antibody-antigen
reactionsto test for
blood types
Varies by country, ethnic group, etc.
Blood typing can be used to:
-show that two samples had different origins (exclude a suspect)
-determine the probability of an individual having a particular blood type
What is the probability that an American has type AB- blood?
4/100 x 15/100 = 60/10,000 or 0.6%
Blood Tests
Determines whether a substance is blood or not, but does NOT distinguish between human and animal blood. Hemastix test
PRECIPITIN TEST
• Determines if blood is human
• An animal (mammal) is injected with sample. If human, animals produce antibodies.
Non-mammals
Oval red blood cells with a visible nucleus
Mammals
• Circular red-blood cells
• No nucleus
Secretors• 80 % of population• Blood type antigens
are secreted in bodily fluids (saliva, semen,
perspiration,gastric and vaginal secretions)
Blood enzymes
Proteins that regulate chemical reactions
Iso-enzymesProtein components into which enzymes can be separated
(1) PGM – an enzyme that has 10 variations
(2) importance- allows forensic scientists to reduce the number of possible sources
BLOOD SPATTER
SIZE AND SHAPE OF DROPSARE AFFECTED BY:
• HEIGHT OF FALL
• ANGLE OF IMPACT
• SURFACE ON WHICH THE DROPS LAND
Shape is determined by the impact angle
Determination of Impact Angle
Measure the length and widthof the stain
• Divide the width by the length to get arc sine of the impact angle
Width / Length = arc sine of impact angle
Ex: width = 2.4 cm
length = 3.1 cm
Ratio of width/length =
2.4 cm / 3.1 cm =
.77419
Use your calculator to get the impact angle
Enter:
“sin -1 (.77419)”
Answer:
50.7 degrees
50.7
Blood spatter labs
1. Height of drops vs. drop size
2. Angle of drop vs.
drop shape
3. Surface texture vs. drop size and shape
The Nobel Prize in Physiology or Medicine – Educational
(Blood type simulation)