anth 245 final exam

the basics of DNA

the basics of DNA

double-strand of sugar-backbone with four bases (A, T, C, G) whose arrangement codes for all proteins in the body

• genes are inherited in these sequence with some recombination during meiosis, organized into 23 chromosomes, coding and non-coding regions

locard’s exchange principle (founding principles of DNA)

you are constantly shedding DNA through sloughed cells and every interaction leaves a trace

individualization (founding principles of DNA)

except for identical twins, you have unique DNA that can identify you, and only you

advancement (founding principles of DNA)

replaces ABO Blood Typing or Serology, class evidence at its best

genetic fingerprinting (RFLP)

DNA is extracted from a sample, then digested with enzymes (from bacteria), pieces of DNA run on through an agarose gel to separate by size (and charge) via electrophoresis, visualized on film as a fingerprint with radioactive tags

• needs more genetic material than modern techniques

tandem repeats

• portions of the human genome that are repeating for a variable number of times

  • 30% of the human genome is comprised of these repeating segments (it’s all “junk DNA” and non-coding)

• outdated technology, was replaced by STR and PCR-based methods

polymerase chain reaction (PCR)

DNA structure and complementary base pairing enables copies to be made of any starting material, just add chemicals

• makes DNA stable & “immortal” through the use of a thermal cycler (it heats and cools the DNA sample)

steps to PCR

1. denature: 1 piece of DNA is turned into two pieces, an increase in temp (to 95 degrees) makes them come apart

2. anneal: a piece of DNA hangs out free and the primers attach to the complementary DNA it’s are trying to copy

3. elongation/extension: the enzyme sits and makes a new copy of the DNA as the original DNA dictates

short tandem repeats (STRs)

regions of DNA where a specific sequence of nucleotides (2-6 base pairs) are repeated in tandem (also “junk DNA”)

• DNA is extracted from biological materials, then needs amplification using PCR techniques to detect between 13/20 loci = Multi-Locus Probe (MLP)

• most commonly used method; these markers are stored in CODIS)

mitochondrial DNA (lineage-based markers)

• found in mitochondria of cells

• only inherited by maternal lines

• high mutation rate can be helpful to see relatedness, but also individuality \n between generations

y-chromosome DNA (lineage-based markers)

• only found in biological males (or those with a genetic abnormality, SRY region)

• highly variable between individuals, but not those blood-related

• Y-STRs can be typed

multiplexing

a technique that can simultaneously detect more than one DNA marker in a single analysis

• more efficient means of testing markers, all at the same time

weight of STR profiles and other forensic DNA evidence

• matches and inclusions fall on a sliding scale: weak associations (mixed DNA samples) to strong (single source)

• need to ask: “what is the probability that two individuals selected at random will have identical STR type/profile?”

product rule

the mathematical product of the frequencies for each marker occurring in the population

• more markers means a smaller frequency occurring together in that combination

M VAC collection

DNA collection on unusual surfaces, more material is needed to generate a useable genetic profile

• 39x more DNA than traditional swabbing with a cotton swab (3min collection)

• more sensitive technique, hence more discretion should be considered when testing items

steps to M VAC collection

1. bath item in saline solution

2. suck up the solution with a vacuum

3. concentrate material on the membrane

4. extract DNA

5. amplify/analyze it

DNA databases

goal: rapid DNA → 90 min turnaround → CODIS

• beneficial with repeat offenders

• STR profiles are a global format for many databases

genealogy databases

• voluntary DNA testing is done to determine relationships, this is the crux of the business/industry

• concerns about ethics and consent, impact of future family members

GEDmatch (2010)

a publicly accessible online database providing genetic genealogy tools to explore family trees

• a database of millions of people who have used these commercial kits

• the government gave permission to police to search GEDmatch

low copy number (LCN) DNA

quantity of DNA that is below the normal level of detection

• for a standard STR profile, only 125 picograms (pgs) are necessary, and if each body cell contains 7 pgs of DNA each – only 18-DNA bearing cells needed

touch DNA

the transfer of DNA via skin cells onto the surface of an object

standard operating protocol of forensic DNA collection

1. properly collect sample containing DNA

2. extract DNA from sample source

3. amplify (using PCR)

4. determine DNA profile

5. compare sample to know DNA (databases, collected, etc.)

forensic DNA collection: detect

detect biological evidence at the scene

• sometimes visual or alternative light source (ALS) needed

forensic DNA collection: photograph

photograph evidence at the scene prior to specimen collection, include in sketches and notes

forensic DNA collection: proper handling

proper handling of bloodstains and fluids

• must be dried in an open envelope before being sealed for transport to prevent mold growth which would degrade DNA

forensic DNA collection: avoid

avoid contamination at all costs!

• use PPE

• separate packaging of evidence

• proper storage: best in a cold, dry place

source of DNA

biological fluid providing DNA

• the suspect can leave DNA on the victim’s body or clothing, an object, and at a location

• the victim’s DNA can be on the suspect’s body or clothing, an object, and at a location

• “witness DNA” can be on any of the above

• can get DNA without the person’s permission if they discard an item

witness DNA

DNA that’s witnessing the crime, it doesn’t belong to the suspect or the victim, but may be pertinent to the case

DNA swabbing

the most commonly used procedure for DNA collection at a crime scene

• special swabs are used that are RNA-free, DNA-free, and have no enzymes that break down genetic material

DNA swabbing methods

• depends on the type of fluid and its condition and context

  1. add 1 drop of distilled water to the swab

  2. touch area and roll the swab around, moderate pressure

  3. allow it to dry before storing

• lysis buffer is needed for a touch DNA sample

• blood stains: one swipe, no smearing

DNA reference samples

genetic materials from crime scenes are the most forensically useful when compared to known DNA samples collected from victims or suspects

collecting DNA reference samples from living bodies

use a buccal swab collection:

• collect check cells that are nucleated epithelial cells for DNA extraction

• swab → burst/lyse cells to extract DNA → isolate → store

• amplify when needed for analysis

SNPs

refers to variations in a single DNA nucleotide that occur at a specific position in the genome

• highly informative of individuals and can be used to establish genetic profiles unique to individuals

• less discriminatory than STRs, database small, random match potential

forensic DNA phenotyping

• “snapshot”: using DNA analysis to produce a computer-generated image of a person or their outward appearance

• “closed source”, peer-reviewed, and no one can check their work

• highlights the limitations of DNA and the use of last-resort methods

• used as a way to generate leads

forensic DNA as a tool

DNA in forensic contexts is often degraded

• in order for PCR amplification to occur, DNA must be intact at primer binding sites and at the STR loci

• interpreting mixtures of DNA can be complicated (more than 3 gets tricky)

• difficult to convey the complexities of biological and statistics to the jury

• when used correctly, DNA profiling is a powerful forensic tool that can be used to quickly eliminate a suspect and reduce the chances of a wrongful conviction

ancient biomolecules applied to forensics

the utilization of molecules to understand past lifeways, ancestry and evolution

• a borrowed technology/methods from the other sciences with an anthropological twist

stable isotopic analysis (SIA)

• measures distinctive “isotopic signatures” because certain abundances record information about material creation

• used to produce “isoscapes” then utilizes the “comparative analysis” aspect, but with empirical values

SIA in forensics

used by forensic anthropologists as a tool to predict region of origin and residence patterns of unidentified human remains using bone, teeth, hair & nails

• aka “where did they live or recently travel”

basics of isotopes

• stable isotope means it has the same number of protons but different numbers of neutrons and will cause no change

• unstable isotope suffer from radioactive decay

• any skeletal/soft tissue or tooth can be sampled for isotopes

isotopes and tissues

• you are what you eat

• isotopes enter the body through food and drink, then are used to make up your tissues, then researchers sample those tissues

  • their analyses decipher these unique signatures to reconstruct lifeways and environments

• isotope located in soil/sediment → plant absorbs it as it grows → animals consume these plants → we eat those animals

isotopes commonly utilized

• carbon-13 (¹³C)

• nitrogen-15 (¹⁵N)

• oxygen-18 (¹⁸O)

• sulfur δ³⁴S

• strontium (⁸⁷Sr/⁸⁶Sr)

MOST common isotope used in diet reconstruction, geographic identity, and environment reconstruction

oxygen-18 (¹⁸O)

carbon 14 (¹⁴C)

used for radiocarbon dating, exploiting the known half-life to date artifacts and specimens

human mobility

• oxygen, sulfur, and strontium isotopes are used to trace human migration

• isotopes can tell if someone is local (to where their body was found)

  • this is established from local animals or the actual geography (soil, water, rock, etc.)

egtved girl

• 3.400-year-old Danish Bronze Age female find

  • ancient human mobility at the individual level using hard or soft tissues

• mobility: she came from outside modern-day Denmark, and traveled over long distances

• diet: terrestrial diet with minimal protein intake

• garments made of non-local wool

• proved that all tissues are helpful

isotopes within the body

• teeth: never change

• bones: have a 7-15 year turnover

• hair: grows 6 inches per year

• fingernails: grow 0.1 inches per month

• all can be tested/used to trace the individual’s mobility and origin

the scissor sisters

• first use of forensic isotopic analysis to point to possible missing person using partial remains

• severed remains of an unknown individual were discovered, no head or fingerprints possible, partial DNA profile obtained

  • analysis of bone and hair showed it was an individual from the horn of Africa, spent the last 7 months in Ireland

forensic isotope analysis

• useful application of molecular testing to gain information about geographic information about unidentified victims

• useful when fingerprints are not available or DNA does not produce a profile/lead

• not as specific as DNA (for victim ID), but traces your past from birth to death

• used to ID victims NOT suspects

bloodstain pattern analysis (BPA)

a forensic technique used to investigate violent crimes using deductive reasoning, experimentation, and reconstruction

• when properly documented, bloodstain patterns found at the crime scene/a particular person’s clothing can make numerous determinations

BPA is an application of?

• physics

• ballistics (projectiles in motion)

• trigonometry

• biochemistry of blood (fluid dynamics)

bloodstain pattern/evidence determinations

• origin/direction of the bloodstains and position of perpetrator

• movement of those involved, especially bleeding individual

• nature of the force used to cause the bloodshed and minimum number of blows

• approximate location of individual delivering blows

• if there is evidence of a struggle or if the assault is one-sided

• sequencing of multiple bloodshed events

• direction of travel and impact angles

• confirm or refute statements made by those involved

crime scene reconstruction

the method used to support a likely sequence of events at a crime scene by the observation and evaluation of physical evidence and statements made by individuals involved in the incident

• reconstruction is still an interpretation of events and is inherently subjective!

physical evidence and crime scene reconstruction

• blood deposited on people, objects, and structures can provide insights into what happened, especially its location, distribution, & appearance

• needs to be properly handled, preserved, and documented

types of bloodstains

1. passive stains (gravity is the primary force; drops, flows, pools)

2. spatter (force in addition to gravity; projections, impacts, gushes, spurts, cast-off, expiratory, back spatter)

3. transfer or altered stains (physically (mechanical) or physiologically (diluted) contact with existing stains; wipes, swipes, transfer patterns)

passive stains

• low-velocity force, only gravity working

• drops or dripping

  • single, multiple, trail

• flow patterns

  • the pattern depends on the amount of blood and surface texture

• large volume

  • saturation (porous)

  • pool (non-porous)

passive stains: repetitive dripping

• can create smaller satellite spatters that look a little like mist from a high-velocity impact just from the constant breaking of the surface tension of the pool the drops are falling into

• caused by blood falling into blood

spatter stains: impact mechanism

gunshots, beatings, stabbings, power tools

spatter stains: projection mechanism

• indicates more than one blow (because first one at least was “clean”)

• may be used to estimate the number of blows

spatter stains: secondary mechanism

satellite spatter (small droplets of blood that are distributed around a drop/pool of blood when the blood impacts the target surface)

spatter stains: GSWs

back spatter (blowback or entrance) or forward spatter (same direction as bullet or exit)

medium velocity spatter

associated with BFT

high velocity spatter

associated with GST

cast-off stains

flings of blood in an arc pattern created by a blood-soaked object; minimum number of blows delivered to victim can be determined from pattern

• blood is projected or thrown from a bloody object in motion onto a surface

projected spatter

bloodstain pattern resulting from the ejection of blood under hydraulic pressure, typically from a breach in the circulatory system

expiration spatter

bloodstain pattern resulting from blood forced by airflow out of the nose, mouth, or wound

• coughed up or expelled from the lungs of the victim

arterial spatter

blood is spurted from a cut artery in large quantities as the heart beats

transfer or altered stains

• clotted (timing)

• diluted (clean-up)

• insects (timing)

• voids (sequencing)

• transfer/contact (sequence)

• smeared/wiped (sequence, clean-up)

  • previous stain, something came in contact • Swipe (sequence, movement)

• swipe (sequence, movement)

  • transfer pattern with movement

bloodstain principles

1. composition of blood

2. fluid dynamics of blood

3. distance fallen

4. surface texture

5. angle of impact

6. directionality

7. area of convergence

8. area of origin

what is blood? (composition of blood)

• average adult holds 5-6 liters in the body

• circulates oxygen & others items

• two main components:

  • plasma (55%)

  • formed elements (45%)

value of blood (physical evidence) for CSIs

1. DNA: from nucleated white blood cells

2. blood type: ABO typing, class evidence (e.g. Secretor, Rh, M/N, Bombay, Duffy...)

3. enzymes: identifying serological profile

4. stains: CS reconstruction

detection/identification of blood

• search: techniques with chemical processes to find blood not visible to naked eye

  • ie: luminol: reacts with iron (heme), visualize a blue glow

• presumptive tests: quick and simple test to determine if a stain is likely blood

  • ie: Kastle-Meyer, Hemastix, Luminol

• confirmation tests: specific and reliable

  • ie: microscopic, hemoglobin, protein tests for humans

*identification is based on experience, but you must test and confirm

fluid dynamics of blood

• cohesion: surface tension of the liquid blood keeps blood droplets together and causes the drops to be spherically shaped

• viscosity is 6 times that of water

• the average size of drop: 0.05 ml, however, there are factors that can influence the size and shape of bloodstains:

  • distance fallen

  • surface texture

  • angle of impact

distance fallen

the diameter of the bloodstain increases as the falling distance increases until the falling distance reaches about 7 feet; the size of the bloodstain remains the same even at higher distances

surface texture

• type of surface blood falls on is an important variable

• a smooth surface retains a round drop

• a rough surface breaks the surface tension and breaks the drop apart into separate spatters and reduces how much the CSI team can deduce from it

• creation of parent and secondary stains

angle of impact

• whether blood drops straight down or at an angle

• tail of the blood drop stain points to the direction of travel

directionality

the direction of the blood droplets as they impact a surface; important factor in determining the origin and trajectory of blood spatter

• it’s where are the drops coming from

• again: the tails point in the direction of motion

area of convergence

• an imaginary line is drawn through the long axis of the stain of selected spatters indicating the direction of travel

• where the lines converge is the area of convergence

• usually at least 7-8 stains are picked to determine this

• this is used for a 2-dimensional perspective

  • can be retraced to determine the location of the spatter-producing event

area of origin

• adding a height dimension to the area of convergence

• must determine angle of impact

• often strings are used for a 3D perspective

documentation of bloodstain patterns

• it is critical to document the appearance and location of each bloodstain for the investigation

• recording not just the bloodstain’s relation to other objects/features but more critically, its physical dimensions since measurements are necessary for reconstruction

• must use scales

• 2 types:

  • grid method

  • perimeter rule method

grid method

grid the entire pattern using strings and stakes, overall, medium-, and close-range photos taken with and without grid

perimeter rule method

arrange rulers around the pattern (perimeter) to be included in photos, then use smaller scales for close-ups

issues with bloodstain patterns

• “CSI effect” is in play here, which is due to the scientific aura that these techniques lend to utilizing BPA

• specialists are out there, but no standard for how much training or experience qualifies as such

• interpretation of bloodstain analysis is NOT STANDARD

• error rates associated with BPA are high; is still SUBJECTIVE

traceology

the scientific examination of trace evidence, which refers to small, often microscopic, physical evidence left at a crime scene that can be linked to a person, place, or object

• scientific interpretation of remnants of earlier activities, especially “contact between two sources”

• ie: hair, fibers, glass fragments, soil, paint chips, gunshot residue or other explosives, polymers, tape, other particles

beginnings of traceology

• credited to Edmond Locard: “whenever two objects come into contact that is always a transfer of material between them”

• Further research developed the subfield to include:

  • methodology refinement: detection, collection, isolation

  • developing techniques: identify and compare unknown substances

  • implementation of methods: prevent cross-contamination at crime scene or lab

  • interpretation of results for active investigations or presentations in court

trace evidence analysis

1. collection and preservation

2. identify the trace evidence (what is it?)

   1. must know what it is before comparison can be completed

   2. many methods, tests to be performed; may be a tedious part of the process

3. comparison

   1. database contain information on substances for comparison

4. results: to be presented in the courtroom

   1. expert testimony delivered during a trial to judge & jury

traceologists

should be experts in chemistry ,microscopic, biology, geology, and physics as well as how to handle such minute evidence

analytical techniques (of trace evidence analysis)

traceologists use a variety of techniques, such as microscopy, spectroscopy, chromatography, and other analytical methods, to examine and identify trace evidence

• the idea is to reconstruct what took place, according to the physical evidence that can be detected

contamination

• any polluting substance that degrades the physical evidence

  • locard’s exchange principle is still in play here, scientifically not always visibly

• it’s likely unavoidable due to locard’s exchange principle

• when you enter a space, you will leave a trace AND you will take a trace of the space with you as well

• once a crime scene is “created,” it starts to degrade

  • trace evidence is likely to be fragile, degradation is critical

contamination of a crime scene

• it’s critical to know what is ”diluting” the original evidence

• contamination is prevented when the scene is secured and technicians have control over the flow of personnel there

• most contamination comes from first responders, then it would be investigative personnel

  • these individuals need to be tracked down, recorded in notes, and then sampled for “elimination

  • their shoeprints, fibers, DNA, fingerprints, etc.

limitations to traceology

the presence of trace evidence does not necessarily prove guilt or innocence, and interpretation of results may be subject to human error or bias. databases are the crux of the power of these analyses so it is paramount they are large, comprehensive, and accurate

advancements in traceology

these have greatly improved the analysis of trace evidence, such as the use of DNA profiling and advanced analytical techniques that are becoming more and more sensitive to detect.

importance of traceology

trace evidence can provide critical information in criminal investigations, helping to link suspects to a crime scene or victim. it can also help to exonerate innocent individuals who may have been wrongfully accused.

sheppard murder

• marilyn sheppard, the wife of a handsome surgeon, was killed by more than 15 blows to her head.

• her husband sam sheppard was convicted of murder in a highly publicized trial and was sentenced to life in prison,

  • he served 10 years - until the U.S. Supreme Court overturned his conviction. in a second trial, sheppard was acquitted, but suspicions about his guilt remained

sheppard murder significance

the first case that used blood pattern analysis to find the perpetrator and prove her husband’s innocence. it’s also the first case where the audience got involved and brought in mass hysteria

• a large stain was left by the killer, who must have been wounded during the struggle. sam sheppard was not injured at all.

forensics and fire

• complex or difficult scenes involving fire that are investigated for crime

• forensic scientists are responsible for the determination of the cause of the fire considering various factors and extensive on-site investigation

• determination must be made by an investigator whose training and knowledge is developed by practical experiences of fire investigation

fire

a rapid, persistent chemical reaction that releases heat and light, especially the exothermic combination of a combustible substance with oxygen (i.e. OXIDATION)

fire tetrahedron

fuel, heat, oxygen, chain reaction

fuel

• will burn and support combustion

• liquid (gasoline), solid (wood), and vapor (propane)

• fuels will only burn in their vapor form

• liquids: flashpoint and fire point

oxidizer

oxidizing agent (O2) is generally present

heat source

energy due molecular activity, an uninhibited chemical chain reaction