Download File - Forensic Science

Forensic Serology
I. History – Karl Landsteiner (1901) theorized that all blood wasn’t the same.
 Realized that transfusions of incompatible blood types caused death due to
agglutinization (clumping due to immune response)
 ABO syp triose
 1937 – Rh Factor identified
 Currently there are more than 100 identified blood factors
 Idea is that no two people will have the same set of blood factors (except for
identical twins) because the factors are genetic.
 Blood – connective tissue made of plasma (50%) and cells (45%)
 Plasma is composed of: water, ions, enzymes, proteins (fibrin)
 Cells – erthyrocytes (red blood cells – contain hemoglobin (transports O2 and
CO2.)), Leukocytes (white blood cells – have an immune function),Platelets
(responsible for bloods ability to clot.).
 Serum is blood with the clotting factors removed.
II. Quick Genetics background:
 DNA > Genes > Chromosomes
 Alleles are alternate forms of a gene
 Alleles are inherited in pairs because there are two parents that provide half of the
DNA
 Humans have 46 chromosomes – gametes (sex cells (eggs or sperm)) have 23
chromosomes.
 A Karyotype shows the chromosomes of an individual ( see how the
chromosomes occur is pairs)




Sex of the individual is determined by the sex chromosomes (Males = XY and
Females =XX)
Sex of the individual is determines by the father.
Paternity testing (Civil Court)
o Looks at blood type and other blood antigens
o Also use HLA (Human Leukocyte Anitgen) – gives a 90% accuracy
o DNA is 99% accurate
III. Blood Types
 ABO system – controlled by the “I” gene, for which there are three different
alleles (IA, IB, i) The lower case letter denotes a recessive allele.
Blood
%
Surface
Antibodies Can
Can give
Genotype
Type
Pop Antigens*
**
receive
blood to
blood
from
A
42
A
Anti B
O+A
A + AB
IA IA, IAi
B
12
B
Anti A
O+B
B + AB
IB IB, IBi
AB
3
A and B
None
O + AB
AB
IAIB
O
43
None
Anti A +
O
ALL
ii
Anti B
 Ag induces IR
 Anitbody – protein in “antiserum” that destroyes or inactivates a specific Ag.
 Agglutination – clumping that results when Ab’s react with Ag’s.
 Type O blood is the universal donor because none of the cells have Ab’s
 Type AB is the universal recipient because serum have no Ab’s
IV. Blood typing
 Blood typing is done by agglutination
o Test the blood with Anti-A and Anti-B serum.
Anti-A + blood
Anti-B + blood
Ag present
Blood type
+
A
A
+
B
B
+
+
A and B
AB
None
O
( + = agglutination)
 Test for the presence of Ab’s using type A and type B red blood cells.
A type RBC’s
B type RBC’s
Ab’s present
Blood type
+
Anti-A
B
+
Anti-B
A
+
+
Anti A and Anti B
O
None
AB

Rh Factor – (“D” antigen )
o Rh positive
o Rh negative
 ABO type and Rh factor are most important in identifying blood
for transfusions.
V. Characterizations of Blood Stains
 Criminalist must answer (when looking at dried blood)
o Is it blood?
o Is it human blood, if not what species.
o If human can it be individualized?
Preliminary Color Tests:
 Benzidine Color test
 common and easy
 carcinogenic
 Phenolphthalein (Kastle-Myer test)
 common, easy, non-carcinogenic
 not specific for blood - needs confirmation.
 Luminol
 blood and luminol floresce
 Can spray a large area
 Very sensitive, can detect blood diluted up to 300,000x
 Doesn’t interfere with later testing
 Hemastix
o Designed to test for blood and urine
o Turns green with mixed with blood
Benzidine and Kastle-Myer banned on the fact that blood has
hemoglobin (Hb) the test have peroxidase like activity that speeds the
oxidation of many organic compounds. So, bloodstain and
phenolphthalein and water (deep pink) - on a swab not on the
specimen.

Takayama & Teichmann tests
o Blood and specific chemicals produce chemicals and Hb
derivatives
o Less sensitive than color tests
o Susceptible to interference from contaminants in the stain.
Human or Animal? Determining the species orgin.
o Use a precipitation test
 Very sensitive
 small amount of blood needed
 diluted or old stains can yield a positive result in a precipitation
test.
 Proceedure:
 A rabbit is caused to produce antiserum to a particular
species,
o Draw the human blood  inject into a rabbit (the
rabbit will produce antibodies against the human
antigens  remove the serum from the rabbit (this
is human antiserum)  mix human antiserum with
the unidentified blood and if you get a precipitation
band (cloudy) the blood is human.
 Antiserums commercially are available for: dogs, cats deer,
cows and many other animals.
o Diffusion Test - uses agar to allow Ag and Ab