Forensic SerologyForensic Serology

BloodBlood

A complex mixture of cells, enzymes, proteins & A complex mixture of cells, enzymes, proteins & inorganic substancesinorganic substances

Fluid portion of blood is called the plasma (55% Fluid portion of blood is called the plasma (55% of blood content)of blood content)– primarily waterprimarily water

– red cells (erythrocytes)red cells (erythrocytes)

– white cells (leukocytes)white cells (leukocytes)

– plateletsplatelets

Searching for BloodSearching for Blood

Tests are based on reducing capacity of Tests are based on reducing capacity of hemoglobin in bloodhemoglobin in blood

Kastle-Meyer testKastle-Meyer test– Phenolphthalein turns pink in presence of blood Phenolphthalein turns pink in presence of blood

and Hand H22OO22

LuminolLuminol– Glows when mixed with bloodGlows when mixed with blood

Erythrocytes Erythrocytes

Transport oxygen from the lungs to the body Transport oxygen from the lungs to the body tissuestissues

Transport carbon dioxide from the tissues to the Transport carbon dioxide from the tissues to the lungslungs

Red blood cells possess chemical structures on Red blood cells possess chemical structures on their surfaces called antigens or agglutinogenstheir surfaces called antigens or agglutinogens

impart blood type characteristicsimpart blood type characteristics

Antibodies or AgglutininsAntibodies or Agglutinins

Types of proteins that are present in the serumTypes of proteins that are present in the serum responsible for ensuring that the only blood cells responsible for ensuring that the only blood cells

that can survive in a person are cells of the correct that can survive in a person are cells of the correct blood typeblood type

Antibodies produced by the A alleles remove any Antibodies produced by the A alleles remove any red blood cells containing B antigens by clumping red blood cells containing B antigens by clumping them togetherthem together

Antibodies produced by the B alleles remove any Antibodies produced by the B alleles remove any red blood cells possessing A antigensred blood cells possessing A antigens

Blood TypeBlood Type

Three types (alleles) of blood type geneThree types (alleles) of blood type gene– A, B, OA, B, O

Each individual inherits one blood type gene from Each individual inherits one blood type gene from their mother & one from their fathertheir mother & one from their father

6 possible combinations (genotypes)6 possible combinations (genotypes) AA, BB, OO, AB, AO, and BOAA, BB, OO, AB, AO, and BO Genotype determines blood typeGenotype determines blood type

Type O BloodType O Blood

Possessed by people whose genotype is OOPossessed by people whose genotype is OO– both parents passed on the O geneboth parents passed on the O gene

have no antigenshave no antigens these cells can be introduced into a person with these cells can be introduced into a person with

Type A or Type B because these cells are not Type A or Type B because these cells are not attacked by the antibodies these people possessattacked by the antibodies these people possess

have both a & b antibodieshave both a & b antibodies can only have other O type cells mixed with this can only have other O type cells mixed with this

bloodblood

Type AType A

Possessed by people with genotypePossessed by people with genotype– AAAA– AOAO

A is dominant to OA is dominant to O Possesses antibody bPossesses antibody b will destroy any Type B red cellswill destroy any Type B red cells compatible with A or O red cellscompatible with A or O red cells

Type BType B

Possessed by people with genotypePossessed by people with genotype– BBBB– BOBO

B is dominant to OB is dominant to O Possesses antibody aPossesses antibody a will destroy any Type A red cellswill destroy any Type A red cells compatible with B or O red cellscompatible with B or O red cells

Type ABType AB

Possessed by people with genotypePossessed by people with genotype– ABAB– A & B are co-dominantA & B are co-dominant

Possesses no antibodyPossesses no antibody can have A, B, AB, or O cells addedcan have A, B, AB, or O cells added Can’t be added to any other blood type Can’t be added to any other blood type

without being destroyed by an antibodywithout being destroyed by an antibody

Blood TypingBlood Typing

Blood typing is done by reacting whole blood with Blood typing is done by reacting whole blood with antibody A and antibody Bantibody A and antibody B

Antibody A will cause A and AB blood to clotAntibody A will cause A and AB blood to clot Antibody B will cause B and AB blood to clotAntibody B will cause B and AB blood to clot Type O blood contains not antigens so will not clotType O blood contains not antigens so will not clot

Precipitin testPrecipitin test

Test which determines whether blood is Test which determines whether blood is human or nothuman or not

Like immunoassay for drugs except for Like immunoassay for drugs except for human bloodhuman blood

Testing for semen samplesTesting for semen samples

Acid phosphatase testAcid phosphatase test– Enzyme found in seminal fluidEnzyme found in seminal fluid– Moist filter paper is rubbed over garment and Moist filter paper is rubbed over garment and

treated with reagentstreated with reagents Purple color means positive for semenPurple color means positive for semen MUP reagent - UV florescentMUP reagent - UV florescent

PSA -prostate specific antigen testPSA -prostate specific antigen test– Immunoassay for protein found only in seminal Immunoassay for protein found only in seminal

plasmaplasma

Secretors vs. NonsecretorsSecretors vs. Nonsecretors

Secretors have A and B antigens in non-Secretors have A and B antigens in non-blood fluidblood fluid– 80% of population80% of population

Nonsecretors don’t have blood type Nonsecretors don’t have blood type antigens in saliva, semen, etc.antigens in saliva, semen, etc.– Remaining 20% of populationRemaining 20% of population

DNA evidenceDNA evidence

ChromosomesChromosomes

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

GenesGenes

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 structureDNA structure

Nitrogenous BasesNitrogenous 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

CODISCODIS

Combined DNA Index SystemCombined DNA Index System National databaseNational database 13 STR’s13 STR’s Population genetics and product rule allow Population genetics and product rule allow

use to determine likelihood of finding use to determine likelihood of finding another individual with same genetic profileanother individual with same genetic profile