Forensic Serology and DNA Analysis Techniques

Serology

the study of bodily fluids

Presumptive Tests

Gives an indication of the presence of the material (MAY or MAY NOT be present)

Sensitivity of Presumptive Tests

Very sensitive; does not need a lot of material

Specificity of Presumptive Tests

Not specific; may get false positives

Luminol

More difficult to interpret results due to luminol having much more false positives

Fluorescein

Produces fluorescence and must be illuminated at 450 nm with an alternate light source (ALS) to be visualized

Phenolphthalein (Phe)

Results should be observed in 15 seconds or less; any pink color change is considered a positive result and warrants further testing

Confirmatory Tests

Confirms the identity of the material

Specificity of Confirmatory Tests

Very specific; only material testing for will give a positive result

Sensitivity of Confirmatory Tests

Not sensitive; usually need a lot of material - may get a false positive if not enough

Takayama Test

Iron in the heme group in blood bonds with nitrogen in pyridine to form characteristic crystals

Species Origin Tests

Tests that determine the species from which a blood sample originated are: diffusion reactions and electrophoretic methods

Ouchterlony Test

Based on antibody-antigen reaction between human blood and human antiserum

Precipitin Test

If the blood sample originated from the same origin as the antigen, bands form between the two wells

Blood Plasma

Made up of many types of cells including red blood cells, white blood cells, and platelets

ABO Blood Grouping

A robust biological marker for blood types

'A' Blood Group

'A' antigen on RBCs; 'Anti-B' antibody in serum; 'AA' or 'AO' genotypes; Population: 40%

'B' Blood Group

'B' antigen on RBCs; 'Anti-A' antibody in serum; 'BB' or 'BO' genotypes; Population: 10%

'AB' Blood Group

UNIVERSAL RECEIVER; 'A' & 'B' antigen on RBCs; No antibody in serum; 'AB' genotype; Population: 5%

'O' Blood Group

UNIVERSAL DONOR; No antigen on RBCs; 'Anti-A' & 'Anti-B' antibodies in serum; 'OO' genotype; Population: 45%

Rhesus (Rh) Factor

A blood group classification based on the presence or absence of the Rh antigen

Seminal Material

Spermatozoa & Seminal Plasma (contains male DNA) is used to determine sexual activity

Ejaculate Volume

2-6 ml; 100-150 million sperm cells per ml (need 100 sperm head for DNA analysis)

Intact sperm

Identification Tests for semen.

Screening

Use of UV light or alternative light source (ALS).

Presumptive test

Semen contains acid phosphatase (AP), a common enzyme that occurs at a very high level in semen.

Brentamine Fast Blue B

Detects acid phosphatase and develops a deep purple color in the presence of semen.

Confirmatory test

Presence of intact spermatozoa in a biological stain has historically been the conclusive test for semen.

Christmas Tree Stain

Traditional method used to visualize sperm cells.

Hematoxylin-eosin Stain

Based on the same premise as the Christmas Tree Stain.

Prostate specific antigen (PSA)

Water soluble protein found in semen.

Enzyme-linked immunosorbent assay (ELISA)

Used to detect p30, based on antibody-antigen reaction.

Time since intercourse (TSI)

Determination may be necessary.

Microscopic Sperm Search

Actual visualization of spermatozoa extracted from a sample.

Morphology of sperm cells

Specific size and shape of head, acrosomal cap, bowling-pin shaped profile, midpiece and tail when present.

Amylase

Digestive enzyme found in high levels in saliva and fecal matter.

Saliva

Can be evidenced in many situations: bite marks, lick adhesives, eating/drinking surfaces, expectoration.

Urine

Can be presumptively tested for the presence of urea or creatinine.

Human Hair Identification

Microscopic examination; DNA analysis can only be done if the hair has a root.

Passive Bloodstains

Created by force of gravity (clots, drops, flows, pooling).

Transfer Bloodstains

Wet blood surface contacts with another surface (wipes, swipes, pattern transfers, general contact).

Impact (projected) Bloodstains

Created when blood receives a blow or force resulting in random dispersion.

Skeletonization

A bloodstain that has been disturbed but still reflects its general shape and size through drying of the outer edge of the stain.

Impact Stains

Depends on angle, direction, point of origin, and/or effect of target surface.

Expirated Blood

Contains air bubbles and saliva.

Mitochondrial DNA

Inherited from mother and located in mitochondria.

Nuclear/Genomic DNA

Large molecule made by linking a series of repeating units called nucleotides, comprised of two strands wrapped around each other in the form of a double-helix.

Nucleotide

Composed of a sugar, a phosphorus-containing group, and a nitrogen-containing molecule called a base.

Bases

Four types: Adenine (A), Guanine (G), Cytosine (C), and Thymine (T).

Complementary-Base Pairing

A-T and C-G.

DNA

The basic unit of heredity found inside most cells of the body that codes for characteristics of a person.

Chromosomes

DNA is arranged within 23 pairs of chromosomes, totaling 46, with each chromosome coming from a parent.

Autosomes

23 chromosome pairs that are not sex chromosomes.

Sex Chromosomes

The last pair of chromosomes, which are X and Y.

Sources of DNA

Blood, semen, saliva, skin cells, hair, and bone can be used as sources of DNA.

Buccal Swab

A method of collecting standard/reference DNA specimens by swabbing the mouth and cheek.

Biological Evidence

Needs to be photographed and recorded before being packaged.

Disposable Gloves

Wearing disposable double non-latex powder-free gloves while handling evidence is required.

Safety Considerations

Wearing face masks, a lab coat, eye protection, shoe covers, and possibly coveralls is required to avoid contamination.

Packaging Biological Evidence

Must avoid plastic or airtight containers to prevent the growth of DNA-destroying bacteria and fungi.

DNA Production of Proteins

DNA directs the production of proteins, which are made by combining amino acids.

Amino Acids

The sequence of amino acids in a protein chain determines the shape and function of the protein.

Nucleotide Sequence

Each group of three nucleotides in a DNA sequence codes for a particular amino acid.

G-A-G

Codes for the amino acid glutamine.

C-G-T

Codes for the amino acid alanine.

Nucleotide Change

If a nucleotide is 'changed', for example a T is substituted for A and G-A-G becomes G-T-G, the 'wrong' amino acid is placed in the protein (in this case glutamine is replaced with valine).

Alleles

Variations of genes.

Phenotype

Observable/physical characteristics.

Genotype

The alleles that make up the phenotype (AA, Aa, aa).

Tandem Repeats

Sequences of bases that are repeated numerous times, acting as a filler/spacer between the coding regions of DNA and offering a means of distinguishing one person from another.

Sequence Polymorphisms

The two sequences of a particular gene are similar (the exact same length) but different at some base pair locations.

Length Polymorphisms

Differ in length.

RFLP

Restriction fragment length polymorphisms (sequence polymorphisms) associated with length differences from relatively long repeating DNA strands.

PCR

Polymerase chain reaction, a technique used for replicating small quantities of DNA or broken pieces found at a crime scene.

DNA Replication

DNA duplicates itself prior to cell division, beginning with the unwinding of the DNA strands of the double-helix.

Denaturation

The process where DNA is heated to separate it, breaking hydrogen bonds.

Annealing

The process where primers (short strands of DNA) are added and hybridize with the strands.

Multiplexing

One can simultaneously extract and amplify a combination of different STRs.

Homozygote

Both alleles are the same length.

Heterozygous

Alleles differ and can be resolved from one another.

STR

Short tandem repeat analysis, locations on the chromosome that contain short tandem repeats that repeat themselves within the DNA molecule.

Amelogenin gene

Gene used for sex determination.

Contamination

The presence of unwanted substances in DNA samples.

Degradation

UV light, sunlight, and moisture degrade DNA, leading to random fragmentation.

Mixtures

Samples containing DNA from multiple sources.

Low template DNA

Samples with insufficient DNA for analysis.

CODIS

Combined DNA Index System, a computer software program developed by the FBI that maintains local, state, and national databases of DNA profiles.

NDIS

National DNA Index System, which began in 1990.

SDIS

State DNA Index System.

LDIS

Local DNA Index System.

Forensic Samples

Profiles from crime scenes.

Criminal Offender Database

Database containing profiles of convicted offenders.

Missing Persons

Database containing profiles of missing individuals.

Genes

Determine the nature and growth of every body structure and positioned on chromosomes.

Genotypes

Pair of allele genes together (genotype AO).

Homozygous

Same alleles.

Heterozygous

Different alleles.

Phenotypes

Person's outward characteristics (phenotype A, doesn't tell us AA or AO).

Chromosomes

On the nucleus of every body cell.

Nucleated cells

All nucleated cells contain 46 chromosomes mated in 23 pairs, except the sperm and egg.