Forensic Serology - My Teacher Pages
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Transcript Forensic Serology - My Teacher Pages
Forensic Serology
Blood
A complex mixture of cells, enzymes, proteins &
inorganic substances
Fluid portion of blood is called the plasma (55%
of blood content)
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primarily water
red cells (erythrocytes)
white cells (leukocytes)
platelets
Searching for Blood
Tests are based on reducing capacity of
hemoglobin in blood
Kastle-Meyer test
– Phenolphthalein turns pink in presence of blood
and H2O2
Luminol
– Glows when mixed with blood
Erythrocytes
Transport oxygen from the lungs to the body
tissues
Transport carbon dioxide from the tissues to the
lungs
Red blood cells possess chemical structures on
their surfaces called antigens or agglutinogens
impart blood type characteristics
Antibodies or Agglutinins
Types of proteins that are present in the serum
responsible for ensuring that the only blood cells
that can survive in a person are cells of the correct
blood type
Antibodies produced by the A alleles remove any
red blood cells containing B antigens by clumping
them together
Antibodies produced by the B alleles remove any
red blood cells possessing A antigens
Blood Type
Three types (alleles) of blood type gene
– A, B, O
Each individual inherits one blood type gene from
their mother & one from their father
6 possible combinations (genotypes)
AA, BB, OO, AB, AO, and BO
Genotype determines blood type
Type O Blood
Possessed by people whose genotype is OO
– both parents passed on the O gene
have no antigens
these cells can be introduced into a person with
Type A or Type B because these cells are not
attacked by the antibodies these people possess
have both a & b antibodies
can only have other O type cells mixed with this
blood
Type A
Possessed by people with genotype
– AA
– AO
A is dominant to O
Possesses antibody b
will destroy any Type B red cells
compatible with A or O red cells
Type B
Possessed by people with genotype
– BB
– BO
B is dominant to O
Possesses antibody a
will destroy any Type A red cells
compatible with B or O red cells
Type AB
Possessed by people with genotype
– AB
– A & B are co-dominant
Possesses no antibody
can have A, B, AB, or O cells added
Can’t be added to any other blood type
without being destroyed by an antibody
Blood Typing
Blood typing is done by reacting whole blood with
antibody A and antibody B
Antibody A will cause A and AB blood to clot
Antibody B will cause B and AB blood to clot
Type O blood contains not antigens so will not clot
Precipitin test
Test which determines whether blood is
human or not
Like immunoassay for drugs except for
human blood
Testing for semen samples
Acid phosphatase test
– Enzyme found in seminal fluid
– Moist filter paper is rubbed over garment and
treated with reagents
Purple color means positive for semen
MUP reagent - UV florescent
PSA -prostate specific antigen test
– Immunoassay for protein found only in seminal
plasma
Secretors vs. Nonsecretors
Secretors have A and B antigens in nonblood fluid
– 80% of population
Nonsecretors don’t have blood type
antigens in saliva, semen, etc.
– Remaining 20% of population
DNA evidence
Chromosomes
Cells contains all the genetic info the cell
needs to exist & to reproduce
In most types of cells, genetic information is
organized into structures called chromosomes
usually X shaped
– Males have XY, females XX
23 pairs in humans
– one copy from mother & one from father
Each chromosome is a single polymeric
molecule of DNA
if fully extended the molecule would be about
1.7 meters long
Genes
Each chromosome contains hundreds to thousands
information blocks called genes
Each gene is the blueprint for a specific type of
protein in the body
only identical twins will have all identical genes
Functions of DNA
To transmit information from one generation of
cells to the next
– Replication: the synthesis of new DNA form existing
DNA
To provide the information for the synthesis of
components (proteins) necessary for cellular
function
Nuclear vs. mitochondrial
– Nuclear contains all genes and is linear
– Mitochondrial contains only genes inherited from
mother and is circular
DNA structure
Nitrogenous Bases
DNA Fingerprinting
Sequencing: a procedure used to determine the order of
the base pairs that comprise DNA
The basic structure of everyone’s DNA is the same
the difference between people is the ordering of the base
pairs
Every person can be distinguished by the sequence of their
base pairs
millions of base pairs make this impractical
a shorter method uses repeating patterns that are present in
DNA
Short Tandem Repeats
DNA strands contain information which directs an
organism’s development called exons
Also contain stretches which appear to provide no relevant
genetic information called introns
– repeated sequences of base pairs
– “junk” DNA
– 30% of genome
All humans have some tandem repeats
Repeats come from the genetic information donated by
parents
STR Analysis
Usually an individual will inherit a different variant of the
repeated sequence from each parent
Restriction enzymes can cut of the sequence of repeats
Number of repeats can be determined by electrophoresis
– More repeats: higher MW: moves less
– Fewer repeats: lower MW; Moves farther
Example: TH01
– A-A-T-G
– From 5 to 11 copies
CODIS
Combined DNA Index System
National database
13 STR’s
Population genetics and product rule allow
use to determine likelihood of finding
another individual with same genetic profile