forensic microscopy final exam

Mitochondrial DNA

Mitochondrial DNA

transmitted only from mother to child

every cell in the body contains hundreds of mitochondria, which provides energy to the cell

Hundreds to thousands of mitochondrial DNA (mtDNA) compared to 2 copies of nuclear DNA in a single cell.

constructed in a circular or loop configuration

each loop contains enough (approx. 16,569 base pairs) A, T, G, and Cs to compose 37 genes involved in mitochondrial energy generation.

Hair Growth Rate

1/2in per month

Basic hair structure

Cuticle

Cortex

Medulla

Cortical Fusi

Ovoid bodies

Pigment Granules

Medullary Index

Medulla /Hair Width

Negroid

diameter - 60-90 um

cross section - flat

pigmentation - dense & clumped

no info on cuticle

undulation - prevalent

Caucasoid

diameter - 70 - 100 um

cross section - oval

pigmentation - evenly distributed

cuticle - medium

undulation - uncommon

Mongoloid

diameter - 90 - 120 um

cross section - round

pigmentation - dense auburn

cuticle - thick

undulation - never

Scalp somatic origin

100-1000 mm long, 25 - 125 um diameter, 0.4 mm/day growth; small root; tapered tip, little diameter variation; various medullation; often with cut tips; may be artificially treated

Pubic somatic origin

pudendal; 10 - 60 mm long; coarse diameter and prominent diameter variation and buckling; broad medulla; follicular tags common; asymmetrical cross section twisted and constricted; may be straight, curved or spirally tutted - root is very fleshy, the tip is abraided since it is rubbing against clothes

Vulvar somatic origin

secondary pubic hair; finer and shorter than pubic hair, may be abraided

Beard somatic origin

facial hair, very coarse: 50 - 300 mm long; large root, irregular structure: often triangular cross section; complex medullation; blunted or razor cut tips; 0.40 mm per day

scales pattern

Mosaic

Petaloid

Double Chevron

Irregular wave

Imbricate (human hair)

Medullary Configuration

Serial ladder

Amorphous cellular

Specific gravity

dry weight / loss of weight in water

Karat (K)

1/24 Pure Gold

Carat (C)

0.2 g or 100 points

1 point = 0.01 ct

Demarcation Line (Dyed Hair)

occurs when hair grows

the contrast between new hair growth and previously colored hair

Pigment aggregates

clumps of pigment irregularly distributed along hair shaft

Discontinuous medulla

patchy and does not run through the entire hair fiber length

Continuous medulla

A medulla pattern where the medulla line is unbroken

Translucent medulla

feather terminology

rachis - shaft of the feather

calamus - root portion of the feather

quill - some feathers don’t have a large shaft (rachis)

quill point - the point that the fiber feathers meet

down feather - has no shaft

barbs - coming off of the main shaft

barbules - coming off of the barbs

nodes - these are on barbs

specialized nodes - indicates what type of species a bird is, they have a certain shape and characteristic, or location to them to help with identification

spermatozoa terminology

acrosome - top layer, part of the head

head - size - length 4.4 um, width 3.2 um

middle piece - size - length 4.0 um, diameter 1.0 um

mitochondrial sheath - in the middle piece

tail - the tail typically falls off, so the majority of the time forensics only has the head cells, there are no measurements for the tail

forensic use phase contrast to identify sperm cells

diamond terminology

crown (or bezel - from the girdle up)

girdle

pavilion (from the girdle down)

facet terminology

table - the largest facet (octagonal shape) on the top of the diamond - pretty important because if you have inclusions or blemishes that are on the table it is real obvious which devalues the stone

bezel

star

upper girdle

lower girdle

pavilion main

culet

Tolkowsky

American Cut

this the standard round brilliant faceting cut

Single Cut

18 Facets

4R rule for glass fracture analysis

Ridges on Radial cracks are at Right angles to the Rear
• The “rear” is the side opposite the impact

SEM signals

With an electron microscope, the forensic microscopist bombard the gunshot residue particles with a electron beam and the result is different signals coming off from the particles

backscatter electrons - comes close to the nucleus of the material that they have, it typically gets backscatter back to the detector, doesn’t lose a lot of energy, most of the electrons that they sent down are coming right back

secondary electrons - the electron beam comes down and not so close to the nucleus of the atom but closer to the outer shells - knocks one of the outer shells out - typically loses some energy and give off some x-rays then goes down a lower orbital shell, the electrons you are getting are actually the electrons from the sample not from the beam

auger electrons - typically emitted from the near-surface region of a material, providing information about the top few nanometers - a surface technique - we don’t do much with this in forensics

characteristic x -rays - you have a spectrometer (EDS & WDS) connected to the detector that will analyze x-rays from the particle -we use this in forensic so we can identify what the material is made out of, with gunshot residue we can go down to a half of micron size particle

Another signal is cathode luminescences signals

resolution limits of microscopy

d = 0.61 λo / n sin θo
Unaided Eye d = 0.1mm (at 25cm)
In LM d=0.2μm (200nm)
In TEM d=0.21nm (2.1Å at 50kV)
In SEM d=3nm (30Å)

Monte Carlo Diagrams

function of accelerating voltage and atomic number

it is a software program - when you hit a particle with a certain electron volts signal, depending upon the atomic number, what it is made out of, the computer program will calculate/extrapolate where those electrons would go and what kind of signal you get off

the smaller the particle, the higher chance you have went pasted the particle and are getting some of the background - the carbon peak gets bigger & the signal to noise ratio gets worse as you blow past the particle

^^ All of this tells the forensic world not to analyze gunshot residue particles smaller than half a micron size

when you have a gunshot residue particle and you want to hit it with an electron beam, analyze the characteristic x-rays to see what that particle is made out of, you don’t want to blow past that little particle because then you will be analyzing the background (stuff that is not part of the gunshot residue particle)

Soil analysis

color - dry it - get all the moisture out, prepare with a Munsell soil color charts

particle size

mineral ID - polarizing light work so we can identify minerals in the soil

(theoretically) instrumental work - x-ray diffraction.

most crime labs don’t get involved in the soil instead they look for artifacts (paint chips, glass, fiber, hair)

down feather/down cluster

the undercoating of waterfowl, approximately 20% of the total covering of the mature bird

a large number of slender filaments or barbs growing in all directions from a single quill point (much superior to feathers as a filling material)

feather fiber

loose barbs or fibers

EDS and WDS

Different types of spectroscopy when it comes to electron microscopy - attaching a spectrometer to an electron microscope

EDS - energy dispersive spectroscopy

cheaper and easier to use - meaning most crime labs do this for gunshot residue

WDS - wavelength dispersive spectroscopy

has a better resolution than EDS

some universities have wavelength dispersive spectroscopy

Everhardt-Thornley Detector

backscatter electron detector - classic one

if it gets to close to the nucleus of the material that they have, it typically gets backscatter right back to the detector, doesn’t lose a lot of energy, most of the electrons that they sent down are coming right back

Solid state backscattered detector

detects secondary electron signals

the electron beam comes down and not so close to the nucleus of the atom but closer to the outer shells - knocks one of the outer shells out - typically loses some energy and give off some x-rays then goes down a lower orbital shell, the electrons you are getting are actually the electrons from the sample not from the beam

X-Ray fluorescence

instead of hitting the particle with an electron beam, you hit the electron coming from the tungsten filament against a source (i.e. rhodium) in a tube which gives off x-rays (x-ray tube), so you can hit your sample with x-rays - which gives lower energy characteristic x-rays coming off

basically the same thing as SEM and electron beam characteristic x-rays - very similar process except that you are using an x-ray tube for the source

what limits gunshot residue analysis?

that the forensic microscopist can’t analyze any gunshot residue particle smaller than half a micron (0.5)

wood terminology

cross section - pretty important because you are trying to see how these wood looks like with a hand lens or a microscope (you can get different types of shapes & sizes to these cells based on how you cut it) - this will tell you if it is a softwood or a hardwood - trying to categorize it - how you cross section it really determines how it looks

bark - protects trees from harsh environmental conditions including weather, pests, disease, and physical damage from animals

cambium - the layer of cells in a plant that provides unspecialized cells to promote growth

sapwood - outer, living layers of the secondary wood of trees, which engage in transport of water and minerals to the crown of the tree

heartwood - the central, supporting pillar of the tree

pith - a tissue in the stems of vascular plants

softwoods - wood from conifers (cone-bearing plants), which usually remain green and do not yearly shed all their leaves, gymnosperms

hardwoods - a category of tree species (angiosperm) that have broad leaves and true flowers with the seed being enclosed

woody monocots - Monocotyledons - any of a group of flowering plants (as the palms and grasses) having an embryo with a single cotyledon and usually leaves with parallel veins and flower parts in groups of three (i.e palm trees)

resin cells - secretes or stores resin - resin protect plants from insects and pathogens

tracheid cells - a long and tapered lignified cell in the xylem of vascular plants

parenchyma cells - carry nutrients - performing metabolic functions such as carbohydrate storage in the growing stem

longitudinal cells - transporting nutrients/water up or down the wood (runs up & down the wood, in general)

ray cells - anything with “ray” comes from the center/middle moves out

ray, longitudinal, parenchyma, & tracheid cells - ALL different types of cells that transport nutrients/water in the plant material

vessel elements - the conducting pathways that constitute the major part of the water transporting system in flowering plants - largest cells in hardwoods, with thin walls and spacious cell cavities (sap conduction)

perforation plates - in tress, there are these long cells that kinda connect to each other - when the come together it is like a cell wall and the nutrients will go in between the two - IF THERE ARE SLOTS then it is scalariform plates

Hair papilla

(dermal papilla) - where the hair follicle is mitotically dividing/growing - part of your scalp, melanocytes that are in here and the melanocytes produce melanin - melanin is being dumped into the cortex of the hair and as it comes up out of that root sheath it becomes keratinized - keratinous dome - keratin hardens (no nucleus in these cells) most of the hair shaft is keratinized cells that do not have a nucleus

Anagen stage

when the cells are actively mitotically dividing (growing), there is a medullary cavity which are air voids in the center of the hair that gives the hair support

this is the type of hair that forensic would do conventional nucleic DNA work - because of the follicular tag & the root sheath

Catagen stage

transitional stage - the area of where the air voids are in (medullary cavity) stops producing the medulla, melanocytes start shutting down

last around a week - very short stage

Telogen stage

the hair is not mitotically dividing, being held in your head by the hair follicle’s club shaped base (can easily fall out), most of the hairs you shed will be this types of hairs

control samples of hair

the amount of control samples of hair is between 50-100

want to have hair from every area of the head (occipital, parietal, frontal)

sequencing glass fractures

observing the existing fracture lines and their points of termination

tempered, laminated, and thermal fractures

thermal fractures - is curved and has a smooth edge, no indication of point of origin

tempered fractures - cannot easily be reconstructed, dices without forming ridges

laminated fractures - 4R rule is not reliable because the two sheets of glass are restricted in movement, remains bulged

muzzle to large distance determinations

As the muzzle-to-target distance increases, the presence of nitrite residues becomes more important in determining distance

electron scattering

occurs when electrons are displaced from their original trajectory

This is due to the electrostatic forces within matter interaction or, if an external magnetic field is present

GSR (gunshot residue) analysis

Automated Particle Analysis
• In control test firings, it has be shown that the concentration of gunshot residue significantly
declines on living subjects after approximately 4 hours.

How is GSR analyzed?
• Historical - Atomic absorption, ICP, NAA, SEM+EDS (manual+semi-automatic)

• These days - Atomic absorption & SEM+EDS (automatic)

• Current Equipment - Digital SEM with motor stage, BSD (backscattered electron detector) and integrated EDS

• Setting of white level thresholds

• Acquisition of BSE image

• Position and size of candidate particles are recorded