Forensics 2 Exam 1

lab safety

closed toed shoes, read all instructions, follow universal safety precautions (treat everything like it’s contaminated, wear PPE  (gloves, lab coat, face mask)

Public Labs

may be police staffed, civilian staffed or a mix of both.  Often funded through police departments-may lead to a sense of bias towards prosecution a court of law. 

Private labs

funded by those seeking analysis.  Often used for outsourcing from public labs or for defense re-analysis.  Also paternity labs, personal info labs

private research facilities

develop and market testing supplies (chemicals and equipment).  Funded by profits from sales

Academia

research methodologies, new tests, train new forensic scientists, etc.

evidence clerks

schedule evidence transfer appointments with lab analysts, track/record evidence submission/transfers; answer general questions concerning each discipline; maintain complete and correct records

analyst

obtain evidence form clerk; examine evidence; take notes; sample/test/observe; interact with prosecutors, LEO, analysts; write reports, review reports, testify; maintain work space

CSI

collect and submit evidence to clerk; discuss collection/evidence with analyst; package evidence; write reports; testify

microscope

 A lens, or series of lenses, used to magnify and resolve fine details of an object.  Used by drug chemists (marijuana exam), Biologists (takayama, semen, hair,fiber), trace analysts(paint glass hair fibers etc.) documents

light microscope

most common in forensics.  Glass lenses. May be compound, dissecting, phase contrast, polarizing (used to examine optical properties), comparison (2 scope connected by optical bridge. Virtual image produced.

electron microscope

not widely used in forensics, mostly in trace analysis.  Use circular magnets and beams of elections

refraction

Bending or Change in direction/velocity of light when it passes from one transparent medium to another-long wavelengths bend less than short ones

dispersion

Separation of white light into component colors

diffraction

The spreading of a wave motion as it passes an obstacle and then expands into the area behind the object

destructive interference

2 waves vibrate in the same plane 180o out of phase-Darkness occurs

constructive evidence

Two waves vibrate in phase-Increased brightness

objective lens

Forms an inverted, side reversed image of observed object

ocular

Eye piece gathers the immediate image produced by the objective lens

magnification of ocular and objective

multiply together for total magnification

field of view

area visible in the ocular

compound light microscope

2D, very small objects (hairs, cells)

dissecting/stero microscope

3D, larger objects (crack in knife blade)

resolution

The shortest distance between two points that the microscope can define as clearly being separate

1857 France

first forensic hair study published-Questions about accuracy soon followed

locards exchange principal

every touch leaves a trace, even if not visable to the eye

1900’s ____ principal

locards

1980

witnesses start to question hair evidence

1984

FBI questions direct match based on a single hair

1990s

DNA enters the picture (hair roots only)

hair

a slender threadlike outgrowth from the follicles of the skin of mammals, composed essentially of keratin and having three anatomical regions: The cuticle, the cortex and the medulla

root

growth point of hair

shaft

projects from skin, made of dead cells, keratin, melanin

cuticle

layers of scales covering shaft, clear to translucent

medulla

central core of cells, appears dark under transmitted light.  May be fragmentary, discontinuous or absent in people usually present in animals. Amorphous in humans, other species may be vacuolated, serial ladder, lattice.  Narrow in human hair, broad in animal hair

cortex

main body of hair, made of spindle shaped cells.  May have corticle fusi (air spaces), pigment granules and/or ovoid bodies

root

pulled hair, large soft root with skin tag; mature hair, small tight root, no skin tag

proximal

root end VS distal-tip (may be cut, split, worn)

fiber

smallest unit of a textile material that has a length many times greater than its diameter. Fibers can occur naturally as plant and animal fibers, but they can also be man-made

common fibers not valuable for analysis

white garment cotton, blue denim

natural animal fibers

sheep wool, angora, alpaca, mohair, silk, feathers

natural plant fibers

cotton, flax, hemp, jute

synthetic fibers

easier to trace, polyester, rayon, nylon, acrylic

serology- medical field

the scientific study or diagnostic examination of blood serum, especially with regard to the response of the immune system to pathogens or introduced substances.

serology- forensics

the detection, classification and study of various bodily fluids such as blood, semen, fecal matter and perspiration, and their relationship to a crime scene

presumptive test

very sensitive screening tests but can only say maybe a particular fluid

confirmatory test

less sensitive, may require more sample or be expensive but can ID a fluid definitively

adults have __ to __ liters of blood

4-6.5

what is blood composed of

plasma, RBC, WBC, platelets

blood

Dynamic tissue, extracellular fluid, delivers nutrients, oxygen, clears waste

blood functions

transport dissolved gases, nutrients, hormones and waste; regulate pH and ion composition; restrict fluid loss; provide immune system; stabilize body temperature

antigens

Substance that may trigger a response from the immune system

antibodies

Protein substance that forms in response to exposure to foreign antigens

plasma

half of blood volume, mostly water with hormones, proteins, glucose and minerals. 

plasma is water _____

soluable

red blood cells

25% of body cells, transports oxygen using hemoglobin, lacks a nucleus and organelle, flexible biconcave disks

white blood cells

Nucleated cells, 1 WBC for every 1000 RBC. Neutrophils, Eosinophils ,  Basophils, Monocytes, and  Lymphocytes

types of lymphocytes

T, B, NK cells

platelets

Small, membrane bound packets of cytoplasm and enzymes responsible for clotting

blood typing

Most common forms are Rh factor (+/-) and ABO typing (Karl Landsteiner developed) becoming a less common tool due to sample size needed and lack of specificity (rarest type 250,000 Americans), most common (over 100 million Americans). Blood type may be secreted into other body fluids

sperm

head (side view elongated pear shape, front view ovoid with acrosomal cap), midpiece and tail (midpiece and tail may be missing on degraded samples) ejaculated will be clearish to whitish to yellowish.

aspermatic males

normal semen except lacking spermatozoa (illness, obstruction, vasectomy). Cells from reproductive tract lining provide DNA component. 

acid phosphate test

found in many body fluids, highest levels in semen. reacts to components of seminal fluid that rely on diet, may be tested ouchterlony or PSA cartilage

sperm confirmatory test

look for spermatozoa under microscope-phase contrast or Christmas tree stain

differences within sperm

may have different shapes, sizes, midpiece size, tail length

amylase

Enzyme that digests starch, in elevated levels in saliva, also in urine, semen, sweat, feces, vaginal secretions and blood. 

Radial diffusion,  phadebas or cartridge tests. 

Does not inherently have DNA, but often cells that have nuclei can be found where amylase levels are high.

vomit

Acidic, destructive to most cells, spermatozoa often can with stand it.  No confirmatory test

urine

Sterile liquid, contains urea and ammonia which may inhibit DNA

feces

Solid waste.  Poor source for DNA, solid stool may have outer surface swabbed for cells from intestines

vaginal secretions

Presumptive test-periodic acid-Shiff reagent to stain cellular glucose (high levels in vaginal secretion)

mucous/tears/sweat

All rely on cell transfer from other sources, no confirmatory tests.

locus

particular location of genome

allele

valid coding sequence of loci

polymorphic

many variable gentic options

homozygous

two identical alleles at locus

heterozygous

two different alleles at locus

electrophoresis

separates molecules according to size and electical charge

fluorescence detection

detection of fluorescently tagged DNA fragments by exciting the fluorophore with a laser and the light emitted is captured by a camera

RFU

relative fluorescent units. unit of measurement in electrophoresis

hardy-weinberg equilibrium

Population gene and genotype frequencies remain constant from generation to generation all assumptions are meet (roughly).  This is robust, and certain issues can be resolved with the application of a theta value

gregor mendal

rules of heredity - something is causing relatives to inherit traits in a reliable fashion

watson, crick, Franklin

determined structure of DNA

Sir Alec Jeffreys

British geneticist developed genetic fingerprinting methods originally used in casework…you don’t need a full genome to compare people

Kary Mullis

American Biochemist, PCR that allowed for automation and widespread use-part of the team that incorporated Taq polymerase

purines

Adenine and Guanine

pyrimidines

thymine and cyosine

Chargaff’s rules

A to T and G to C

introns

polymorphic useful for forensics

loci nomenclature

D=DNA;  #=Chromosome number; S=single copy sequence; long#=locus number

( ie D3S1358) or named after a near-by gene

DNA exam

have source material (found by serology) blood, semen, hair, etc. Take a small sample, lyse cells, separate DNA from other cell bits, quantify the DNA in the sample, Amplify the sample, electrophorese, analyze

automation kits

becoming more popular, phenol chloroform isoamyl alcohol still the gold standard. Can use different filters/columns to further purify.

differential extraction

separates sperm cells from other cells

peak height ratios

the RFU ratio between two peaks within a locus. Dependent on amount of DNA contributed, modelled by STRmix.  Imbalance can (and will) occur.  Peak height will vary between loci

stochastic effects

Preferential amplification of one allele occurs with Low concentration samples

shutter

“strand slippage” When template or replicate loops and reanneals.  Results in a strand either one repeat shorter (n-4, n-5) or longer (n+4, n-5) than the true allele.

spike

Much sharper than allele peaks.  Usually appears in all colors.  Caused by dust or urea crystals in the capillary

dye blob

Much broader than allele peak. Usually appear in one color. Caused by dissociated primer dyes

binary genotyping

Either it is an allele or it isn’t.  Visual interpretation of electropherogram (epg) using thresholds; stutter percentages; etc.  Easiest for single source samples, less useful for mixtures.  Calculate CPI or (m)RMPs

probabilistic genotyping

Allows for complex mixture interpretation using Continuous biological modelling.  Alleles can be maybes.  Calculate LRs

Box A

indicate the Locus you are analyzing (ie D3S1358).  The space below the box represents all of the alleles that are possible for that locus.

Box B

the peaks indicate the allele call (here X and Y), the peak height in rfu (5035 and 5929) and the position (81.54 and 87.66) as determined by the ILS. This sample is a male (XY).