Forensic Science Test 2

Fingerprints

Unique patterns made by friction ridges (raised) and furrows (recessed)

Francis Galton (1892)

Published Finger Prints, discussed anatomy of fingerprints + ways to record them + described minutiae

Dermal papillae

Boundary of cells separating the epidermis from the dermis

Admissibility in court (fingerprints) is based on:

permanence and individuality

What determines the individuality of fingerprints?

Friction ridge characteristics (minutiae)

How many ridge characteristics/points must be present in a pair of fingerprints to be considered a match?

8 (in DE) to 16 points present in a pair of fingerprints (a known: from person and unknown: from crime scene)

Ridge patterns

loops, whorls, arches

What is a loop fingerprint pattern?

Ridges flow in from one side and exit the same side; has one delta on opposite side, 60%

2 types of loops

radial loop, ulnar loop

What is a whorl fingerprint pattern?

Bulseye, circular or spiral pattern, 35%

Types of whorls?

Plain, double loop, central pocket, accidental

What is an arch fingerprint pattern?

Ridges enter one side and exit the other with no looping, 5%

2 types of arches

Plain and Tented

2 Focal points in fingerprints

Core & Delta

What are Minutiae in fingerprints?

Small ridge details that make each fingerprint unique

Types of minutiae patterns

Ridge ending, bifurcation, island/point/dot, lake, opposed bifurcations and cross, bridge (crossover), double bifurcation and trifurcation, and hook (spur)

What is AFIS?

Automated Fingerprint Identification System; a computer system used to store and compare fingerprints to potentially match and help identify individuals in investigations.

Patent fingerprints

3D impressions left when finger is contaminated with soft materials like clay, wax, or soap

Plastic fingerprints

2D impressions left when a finger is contaminated with a substance like blood, ink, dirt, etc.

Latent fingerprints

Invisible fingerprints left by sweat and oils; require chemicals or methods to see

Methods of detecting fingerprints

-Powders

-Super glue (cyanoacrylate) vapors

-Reflected UV Imaging System (RUVIS)

-Other methods such as ninhydrin and laser light

Preservation of detected prints

Preserve, photograph, lift with adhesive tape, and then scan and edit

What is DNA analysis?

The study of DNA to identify a person by comparing genetic markers and patterns

Sir Alec Jeffreys (1985)

Examined variable number tandem repeats (VNTRs) by restriction fragment length polymorphism (RFLP)

Sources of DNA Evidence

Biological materials that contain DNA used for forensic analysis

Hair Structure

medulla, cuticle, and cortex

In Hair DNA, where is mitochondrial DNA and nuclear DNA found?

shaft, root

Bone Structure

Osteocytes, osteoclasts, and osteoblasts

Where is DNA found in teeth?

Pulp

Other cellular sources of DNA

Spermatozoa, vaginal cells, and buccal cells

DNA Extraction methods

-Cell and tissue disruption: breaking open sample

-Lysis of membranes and organelles: releasing DNA

-Extraction: removing proteins and other materials

Organic extraction

Phenol & chloroform

Storage

Proper preservation of DNA samples to prevent degradation

Flinders Technology Associates (FTA) Cards

Special cards used to collect, store, and preserve DNA samples for reference

Chelex® Method

A quick extraction method that uses resin to isolate DNA

Differential Lysis

Technique used to separate sperm cells from other cells (commonly in semen samples)

DNA Quantification

The process of determining how much DNA is present in a sample

Quantification Charts

Show if DNA is too much amplified (copied), too little amplified, or within the optimal range for analysis

Polymerase Chain Reaction (PCR)

A technique used to amplify (make many copies of) DNA

Each cycle of PCR

Denature, anneal (2 primers), extension (DNA synthesis)

Factors affecting PCR

Template degradation, low copy number of template, inhibitors, contamination

Real-time Q-PCR

Amount of PCR product (amplicon) correlates to the initial DNA concentration

DNA copy

Amplicon

Quantitative PCR (Q-PCR)

A method used to measure the quantity of DNA in a sample

TaqMan method (most popular Q-PCR method)

-Two primers and one probe, which has a fluorescent (reporter) dye on 5' end and a quencher molecule on 3' end

-As long as probe is intact, fluorescence is quenched

-During DNA synthesis, Taq polymerase cleaves the probe, releasing the dye

Functions of the Delaware State Police Bureau of Identification

Fingerprint analysis and biometrics, including facial recognition.

Four steps in fingerprint analysis

Analysis, Comparison, Evaluation, Verification ACEV

Matrix (Fingerprints)

Material left by a finger that forms a print, such as sweat, oils, and amino acids

Substrate (Fingerprints)

The surface on which a fingerprint is deposited

Development Medium (Fingerprints)

Substance used to make latent fingerprints visible (e.g., black powder)

Deposition Pressure (Fingerprints)

Amount of pressure used when a fingerprint is left; more pressure can produce a darker print

Level 1 Detail (Fingerprints)

Latent print details, orientation, ridge flow, core, deltas, pattern types, class characteristics of friction ridge skin.

Forensic DNA Profiling

The process of analyzing specific regions of DNA to create a unique genetic profile for identification

Short Tandem Repeats (STRs)

Repeating sequences of DNA used in forensic profiling; variation in repeat number helps distinguish individuals

Each STR locus contains what?

core repeat region

How many STR loci used in forensic science in the United States

20

STR Locus Naming (Example: D5S818)

D = DNA, 5 = chromosome #, S = single copy sequence, and 818= 818th locus described on chromosome)

Repeat lengths

Dimeric (2), trimeric (3), tetrameric (4), pentameric (5), and hexameric (6)

Tetra and Pentameric repeats

Most commonly used in forensics because they are more stable and easier to analyze

Core Repeat Sequences (STRs)

The number of repeats determines the allele number (simple or core repeats); one continuous repeating sequence.

Example: Allele 10 of D5S818; (AGAT)10 (designated allele 10 because there are 10 repeating subunits of a tetrameric sequence)

Compound repeats

Made of more than one repeating sequence type.

Example: Allele 14 of D8S1179; (TCTA)2, (TCTG)1, and (TCTA)11 (2+1+11 = 14)

Complex repeats

Multiple repeat types plus intervening sequences

Example: allele 24 of D21S11; (TCTA)4, (TCTG)6, intervening sequence (43 base pairs with 8 repeats), (TCTA)6 (4+6+8+6 = 24)

Forensic STR Analysis

-Multiplexing

-Amplicons have fluorescent label

-Capillary electrophoresis

-Electropherogram, allelic ladder

-Factors affecting STR profiling

-Mixed samples

Multiplexing

Simultaneously detects more than one DNA marker

Capillary electrophoresis

Method used to separate and detect out STR alleles based on size.

Electropherogram, allelic ladder

-One peak at a single locus: homozygous

-Two peaks at a single locus: heterozygous

Factors affecting STR profiling

Mutations, chromosomal and gene duplication, stuttering...

Mixed Samples

DNA samples containing more than one individual; High stutter ratio

Interpretation of STR profiling

-Inclusion, exclusion, and inconclusive results

Inclusion (STR Result)

The DNA profile is consistent with the reference sample and cannot be excluded

Exclusion (STR Result)

The DNA profile does not match the reference sample and is ruled out; if genotypes are different between the 2 profiles

Inconclusive (STR Result)

The DNA evidence is insufficient or unclear to determine a match or exclusion

Possible outcomes of STR match

Suspect deposited sample, suspect did not deposit sample but has match by chance, suspect did not deposit sample and match is a false positive due to contamination or lab error.

Combined DNA Index System (CODIS)

A national database system used to store and compare DNA profiles for forensic identification

3 Levels of CODIS Architecture

-National DNA Index System (NDIS)

-State DNA Index System (SDIS)

-Local DNA Index System (LDIS)

CODIS Indexes

Categorize DNA profiles entered in the database

Convicted Offender Index

Case-to-offender searches (offender hit)

Forensic Index

Case-to-case searches (forensic hit)

Other CODIS Indexes

Arrestee

-Missing Persons

-Unidentified Human Remains

-Biological Relatives of Missing Persons

-Pedigree Tree

2015 Expanded FBI STR Population Data

Includes allele frequencies for the autosomal STR loci as determined in 11 populations

Probability of finding a given STR profile

Product rule

Ex: 1.68 x 10^-15 or 0.00000000000000168.

Rapid DNA instruments

Automated systems that perform DNA analysis quickly, often used for fast forensic identification.

-mobile unit

Ex: RapidHIT ID System (IntegenX)

Sex typing

Determining biological sex using genetic markers like Amelogenin (AMEL) loci

-AMELX

-AMELY

-AMELX only indicates female; AMELY and X indicates male

Mitochondrial DNA profiling

mtDNA is maternally inherited (non-Mendelian inheritance)

Main advantages of mtDNA in forensics

More copies in cell than nuclear DNA, Less subject to degradation, Useful in hair shaft, bones, and decomposed samples

Main disadvantages of mtDNA in forensics

Less polymorphic than nuclear DNA, Low power of discrimination, More subject to contamination during analysis than nuclear DNA.

Interpretation of mtDNA

Exclusion: sequences are different

Cannot exclude: sequences the same

Inconclusive: questioned sample and reference sample differ by a single nucleotide

Strength of DNA Profiling Results

The statistical weight used to describe how likely a DNA profile match is in a population

Allele frequency (p)

Number of alleles of one type at a given locus divided by total number of alleles

Allele Frequency Table

A chart showing how common each allele is in a population

Genotype frequency (P)

number of individuals with one genotype divided by the total number of individuals in a sampled population

Hardy-Weinberg principle

-Equilibrium

-Genotype frequencies can be predicted by the allelic frequencies

-p2 or q2 for homozygotes

-2pq for heterozygotes

-p2 + 2pq + q2 = 1

Conditions for equilibrium

Large population, mate randomly, lack mutation, migration, and natural selection

Product rule of probability

Calculating combined or total probability match (Pm) for two or more loci

Innocence Project

A nonprofit organization that uses DNA testing to help exonerate wrongfully convicted individuals and reform the criminal justice system

Pharmacokinetics

Absorption into bloodstream; How drugs act in our body

Routes of administration

Oral, rectal, inhalation via nose or mouth, smoked or inhaled (lungs), nasal insufflation, intravenous (IV) injection, sublingual, transdermal, ocular, etc.

Gastrointestinal tract (GIT) Absorption

Small intestine is the major site

First-pass effect/metabolism

Concentration of a drug is greatly reduced before it reaches the systemic circulation

After oral ingestion, enter ___ before entering circulation

Liver