Forensic Fingerprint and DNA Evidence

What is a fingerprint?

-Unique Ridges on the tips of fingers

-Individual Evidence

-Created by the Basal Layer (only this layer can be damaged)

-Leave Imprints

~ water, oil, and salts

-formed at 10 weeks in womb

-stays the same throughout life

-Damage is permanent

-Loss of Prints is Rare

Types of Fingerprints?

Patent; visible fingerprint that happens when fingers coated with blood, ink or some other substance touch a surface and transfer their fingerprint to that surface.

Plastic: Three-dimensional fingerprint made using soft material such as clay, soap, or putty

Latent; Concealed fingerprint made visible through the use of powders or forensic techniques

Taking Fingerprints

10 Print Card- both hands, full hand fingerprint, and finger roll,

Live scan- Digital Scanning

Fingerprint Identification

Arches- 5%, Plain arch and delta(triangular point) tented arch.

Whorls- 30% (deltas), plain (1 or more ridge make complete loop, line between deltas crosses circle), Central Pocket Loop (1 or more ridge make complete loop, line between deltas does not cross circle), Double loop( 2 separate loops, line between deltas crosses at least 1 circle), Accidental (combination of different patters, Arch+ Loop)

Loops- 65%, exit and enter from the same location, has a core, Radical( towards thumb), Ulnar( away from thumb)

***** EACH FINGER CAN HAVE A DIFFERENT PATTERN******

Ridges have unique Patterns called MINUTIAE

  • Ridge ending

  • Fork (bifurcation)

  • Island ridge (short Ridge)

  • dot (very short Ridge)

  • bridge

  • Spur (hook)

  • Eye (enclosed island)

  • Double bifurcation

  • Delta

  • Trifurication

***EACH FINGER CAN HAVE MANY DIFFERENT MINUTIAE*****

What is the Value of Fingerprints?

  • Individual- Even identical twins have different fingerprints

  • Fingerprints will remain unchanged during Lifetime

  • Have ridge patterns that can be systematically classified

What is needed for fingerprint Match?

  • Matching Pattern( ridge, whorl, or loop)

  • 10-16 specific minute matches

Fingerprints on the crime Scene

  • Patent and Plastic prints are visible

  • photograph, recover, and bag

  • Latent prints are invisible- further treatment needed

Visualizing Latent Prints

  • Flat surface- dusting- carbon, metal or magnetic \

  • Paper- Ninydrin- spray

  • Plastic/glass/metal-cyanoacrylate Vapor

  • wood-sliver nitrate

  • cardboard- iodine fuming

How to lift finger prints

Dust-tape- note card or paper

Limitation of fingerprints

  • 1995: 1 in 5 fingerprint examinations made false identification

  • Today: All fingerprint analysis must be reviewed by 2 examiners

  • 98.6% accuracy on single fingerprint

  • 99.6% accuracy on two fingerprints

What is DNA?

  • Molecule: DeoxyriboNucleic Acid

  • Function: store genetic material, contains the code for proteins

  • DNA-RNA- Proteins

  • Location: Found in all cells, Prokaryotic- free flooding, Eukaryotic- Nucleus

Molecule: Deoxyribonucleic aicd

  • Double helix made up of nucleotides

  • phosphate group

  • Deoxyribose sugar

  • Nitrogenous base

  • 4 bases- G(guanine), A (adenosine), T(thymine), C(cytosine), C-G and T-A

Function: Stores Genetic material

  • Central Dogma of Biology: transcription and translation

  • Proteins determine different traits

  • DNA(CAGGAC)- Transcription(Nucleus), mRNA (GTCCTG)- Translation(ribosome), Protein: (Glu-Asp)(Amino Acid)

  • Human Genome is 3.2 billion Nucleotide

  • Only 5% of the genome codes for proteins

  • Gene sequence of DNA that codes for protein- Exons( Region that are expressed)

  • 95% does not code for protein- Introns( Non-coding regions)

  • 99.9% of DNA is identical between all humans

  • 0.1% of the genome is unique to an individual

How is DNA structured in a cell?

  • Chromatin: Wrapped around proteins

  • Histones and Nucleosomes

  • When cells Replicate - DNA condenses, and Nucleus dissolves

Human Chromosome- 46 total chromosomes, 44 autosomes (non-sexual) and 2 sex chromosomes (xx or xy).

Karyotype- number and appearance of chromosomes

Chromosomes are homologous “Same information”

Alleles; Different versions of a gene

How are Alleles inherited

one allele is inherited from each parent. each parent has 2 alleles for any trait. Alleles can be different= Heterozygous. Alleles can be the same= Homozygous.

DNA IS IT HUMAN?

Chimpanzee+ Potato= 48 chromosomes

Human= 46 chromosomes

Chicken_ 78 chromosomes

Frog= 26 chromosomes

Pea= 14 chromosomes

Radish, Cabbage, Citrus, and Passion fruit= 18 chromosomes

Species can have the same number of chromosomes, DNA sequencing is preferred

Chromosome number varies between species

Karyotyping could be used to determine species origin of a sample

DNA at a Crime Scene

DNA can be extracted from almost any cell (fat, skin, Sex, Blood)

Red Blood cells do not have DNA

DNA collection guidelines

Avoid Cross Contamination- Wear disposable gloves, use disposable instruments, avoid touching where DNA can be, avoid talking, sneezing, or coughing.

Prevent Environmental Degradation- Air- dry evidence, freeze evidence that cannot be dried, use new paper bags and envelops, keep samples dry and cool, Humidity can destroy DNA.

GOAL: Create DNA profile/ DNA fingerprint that demonstrates the unique characteristics of an individual’s DNA.

Can be used for identification and comparissons

  • extract DNA

  • Make copies of DNA Sample (PCR)

  • Identify and Isolate unique DNA

  • Cut and Analyze DNA( Gel Electrophoresis)

Extract And Copy DNA: Cell harvest- cell lysis- protein removal- DNA binding- wash- DNA elution. Cells are split open( Lysed). All other molecules are washed away. DNA extracted will be too little to analyze. Amply or copy it using polymerase Chain Reaction (PCR)- Thermocycler, Denaturation (heat separates DNA Strands), Anneal (Primers Provide Start), Extend ( Polymerase builds new strands)

Cyles Repeates to make More DNA