Transcript Blood Type Testing (anti-serums)

WARM-UP
1) Do you know your blood type?
2) Have you ever donated blood?
3) Have you ever received a blood
transfusion or know someone who has?
4) What do you think is the importance of
blood typing in Forensic Science?
5) What are you looking forward to in this
unit, what are you dreading?
Forensic Serology
Identification Using Blood Groups
Forensic Serology
Serology – term used to describe a broad range of
laboratory tests using reactions of blood serum and
body fluid
The serology section of a forensic laboratory may
deal with any or all of the following:
• blood typing
• characterization of unknown blood
• stain patterns for crime reconstruction
• paternity testing
• semen or saliva identification
• DNA techniques used for identification
Forensic Characterization of Bloodstains
Three questions that must be answered by the
forensic investigator:
1) Is it blood?
Benzidine Test
Kastle-Meyer Test
Hemastix (o-tolidine, TMB)
Luminol Test
2) Is it human blood?
Precipitin Test
3) Can it be associated with an individual?
Blood Type Testing (anti-serums)
Blood Antigens
On the surface of red blood cells are chemical
structures (proteins) called antigens
The presence of antigens allow a living system to
recognize foreign biological substances
Antigens also impart specific characteristics to the
red blood cells. These characteristics can be partly
used to identify individuals
Human red blood cells have more than 15 different
antigen types that have been discovered
Blood Typing
Blood typing involves determination of the antigens
present on an individual’s red blood cells (RBCs)
The two most common blood typing systems used
are the A-B-O method and the Rh method
type A blood – contain “A” antigen on RBCs
type B blood – contain “B” antigen on RBCs
type AB blood – contains both A and B antigens
type O blood – contain no A or B antigens
Rh+ blood – contain Rh antigen
Rh- blood – no Rh antigen
Blood Typing
Blood also contains antibodies – proteins that
recognize and bind to certain, specific antigens
Blood Type
Antigens on RBC
Antibodies
A
A
anti-B
B
B
anti-A
AB
AB
none
O
none
both A & B
Rh Factor: A red blood cell that contains Rh antigens is said to
be positive; no Rh antigens is said to be negative. The antibody
is called “anti-D”
Blood Typing
- Red blood cells
containing A antigens
do not combine with B
antibodies
- Red blood cells
containing B antigens
are clumped together
(blood clot) in the
presence of B
antibodies
Blood Typing
Human serum containing specific
antibodies can be purchased
Separately mix a drop of
unknown blood sample with
drop of each anti-serum
Reaction between blood
and anti-serum
No reaction between
blood and anti-serum
Blood Typing Example
A sample of unknown blood is mixed with three antisera samples:
Tube 1 (Anti-A): No reaction
Tube 2 (Anti B): No reaction
Tube 3 (Anti Rh): Cloudy reaction
In terms of the A-B-O and Rh systems, what type
blood is the sample? O positive
The ABO antigens are not confined to RBC; 80% of
Americans are secretors, same antigens found on
other cells
Principles of Heredity – Vocabulary Review
Gene: basic unit of heredity, consisting of a DNA
segment located on a chromosome.
Chromosome: a threadlike structure in the cell nucleus,
along which the genes are located.
Egg: female reproductive cell
Sperm: male reproductive cell
Zygote: cell arising from the union of an egg and a
sperm cell
X-chromosome: female sex chromosome (XX – female)
Y-chromosome: male sex chromosome (XY – male)
Principles of Heredity – Vocabulary Review
Allele: any form of a gene located at the same point on a
particular pair of chromosomes
Homozygous: a gene pair made up of two similar alleles
(dominant/dominant AA & BB; recessive/recessive OO)
Heterozygous: a gene pair made up of two different
alleles (dominant/recessive AO & BO; co-dominant AB)
Genotype: pair of allele genes in cell
Phenotype: physical manifestation of a genetic trait
(shape, color, blood type)
Ex. Phenotype: Type A
Genotype possibilities: AA or AO
Punnett Square Practice
If a mother has type AB blood, and a father has type O
blood, answer the following questions:
1) What is the genotype of the mother and father?
2) What are all the possible genotype combinations
their offspring could have? Fill out the Punnett
square below.
A
- 50% Chance
offspring is Type A
- 50% chance
offspring is Type B
O
O
B
AO
BO
AO
BO
Paternity Testing in Forensics
• Genotyping of blood factors useful applications for
transmissions of blood characteristics, but no direct
relevance to criminal investigations
• Has implications in disputed-paternity cases (civil,
not criminal cases)
• Resolved by comparing blood group genotypes of
suspected parents and offspring. Does not always
mean the suspect is the father, as many other males
may also have the same blood type
• HLA (human leukocyte antigen) test looks at white
blood cell antigens (90% accurate)
• DNA test procedures (over 99% accurate)
Punnett Square Practice
Jane has type AB blood, and John has type O blood. If
Jane’s child has type AB blood, is there a possibility
that John is the father?
A
B
O
AO
BO
O
AO
BO
In the words
of Maury
Povich:
“John… You
are NOT the
father”