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Trace Evidence > Lecture 15&16 - Hairs > Flashcards

Lecture 15&16 - Hairs Flashcards

1
Q

can microscopical hair examination lead to individualisation

A

no, it can’t be said that an known hair comes from a specific person based on microscopy alone

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2
Q

how can the analysis of hairs lead to individualisation

A

recovery of DNA from the follicle if present

but DNA is not trace evidence

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3
Q

give 6 reasons why hair is a good form of trace evidence

A

found on all humans and mammals and in large amounts (estimated at 100,000-200,000 on the scalp)

easily overlooked by criminals clearing up

easily transferred from a person to another/object

constantly being produced and shed

very stable - resistant to chemical and physical degradation

can get DNA from follicles

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4
Q

what two bits of information can hairs give that help with investigations

A

investigative leads and help with reconstruction of events

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5
Q

what are hairs made of

A

proteins - specifically keratins

which are very robust so allow persistence

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6
Q

why is it difficult to differentiate between hairs from different sources

therefore what techniques are more useful than chemical methods

A

because all true hairs have the same basic chemistry so chemical techniques are not the most useful

elemental analysis and spectroscopic techniques

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7
Q

what can looking at the isotope ratios of elements in hair provide and how is this done

A

can give locations an individual has travelled to based on the the change in drinking water at different locations

diet and use of substances of abuse can also affect the elements hairs are made of

done using mass spectrometry

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8
Q

what are the three types of hairs

A

Lanugo = formed in uterus, shed before or shortly after birth - rarely found unless a newly or unborn child is involved

Vellus = fine and short (1mm approx), tend to be lightly coloured or unpigmented, present on almost all skin surfaces like nose, ears, forehead.

terminal = hairs macroscopically visible

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9
Q

where are vellus hairs not found

A

palm of hands and feet

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10
Q

what are the two types of terminal hairs

A

primary hairs = head, eyelash, eyebrows

secondary hairs = pubic, underarm, beard

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11
Q

where are the most commonly analysed in forensic hairs from on the body

A

head or pubic hair

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12
Q

describe the phases in the growth of a hair

A

anagen = active growing phase of hair from root outwards from skin

catagen = transition phase where growth slows and stops

telogen = resting phase where minimal force is required to remove hair and natural shedding occurs

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13
Q

what is the shedding of hair affected by

A

a range of environmental factors e.g weather

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14
Q

what are the 4 layers of a hair

A

cuticle = outermost layer

cortex = main bulk of hair

medulla = innermost layer - NOT ALWAYS PRESENT - not well understood/studied

cell membrane complex = interface between cuticle and cortex

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15
Q

what is the cuticle of a hair responsible for

A

largely for the chemical resistance from the environment allowing hairs to persist

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16
Q

what is the cortex of a hair responsible for

A

the mechanical properties of a hair

most pigmentation here allows for colour

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17
Q

what is the purpose of a hair follicle

A

this is where the hair grows from - changes shape and size

the presence or not of this could indicate the nature of how the hair was removed - pulled or cut or naturally shed

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18
Q

what phase of the hair cycles are most and least hairs in

A

most = anagen phase
least = telogen phase

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19
Q

where does the variation in hair growth between individuals lie

A

age
dependent on the individual
ancestral groups

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20
Q

what lead to the appearance of grey hairs

A

pigment in hairs stops being produced

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21
Q

what could give characteristic features in the analysis of hairs

A

use of bleach or hair dye
heat damage
other hair products

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22
Q

what are the two main methods seen in the collected of hair evidence

A

forceps = good for individual hairs but can damage hair if too much pressure used (seen by bulging of the hair under microscope)

tape lifts = good for collecting hairs from large SA and prevents damage from forceps

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23
Q

what is beneficial when analysing hair evidence from suspects and how is this done

what is the recommended amount from ENFSI guidelines

A

a representative number of hairs being taken by combing or plucking due to variation even within an individual

combing = better as less pressure and less damage likely

recommended 20 hairs from 5 different head regions

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24
Q

what is the updated analytical workflow when analysing hair evidence

A
  1. gross examination, recovery and collection
  2. prelim evaluation of physical characteristics
  3. microscopic techniques
  4. DNA analysis
  5. SEM (maybe TEM)
  6. IR and Raman - spectroscopic techniques (non destructive)
  7. chromatographic techniques and mass spec (destructive)
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25
what is the benefit of using SEM in hair analysis
gives morphological features and surface analysis
26
at what stage in the analytical workflow of hairs do we normally stop at
microscopic techniques
27
what microscopic techniques are useful in the analysis of hair evidence
stereoscopic comparison polarised reflected light bright field these two only used when more info is needed: fluorescence SEM - electron microscopy not light (rest are light)
28
what 4 characteristics of hairs can be revealed at macroscopic level (initial examination)
macroscopic colour - blonde, red, black, brown length - in mm general shape and curliness - straight, wavy, curly, kinked approx diameter - thin, medium or thick
29
what can be used to help suggesting the colour of a hair
different background giving more contrast
30
what can macroscopic observation be improved using
microscopic techniques
31
what are the first two types of microscope often used in hair analysis
compound light polarised light
32
in order to make comparisons how should the unknown and known hairs be visualised
under microscopes with the same settings and on the same mounting media
33
how can different mounting media affect the visualisation of hairs under microscopy
the difference in refractive index between the sample and the mounting media affects the contrast and therefore how well the sample is to be seen
34
what 9 features of hair can be seen under microscopes that help with the discriminative value of hair evidence
colour cosmetic treatment thickness range (micrometers) cross sectional shape shaft irregularities general hair damage (split, frayed, broken) biological damage = insect bites, fungal or bacterial activity material adhered to it - blood, nits, particles/residues non-root morphologies - cut, rounded or broken
35
what does microscopic analysis of the cuticle include
colour - indicates use of dyes presence or absence of pigment granules inner margin analysis thickness - thin medium thick damage scale protrusion
36
what does microscopic analysis of the cortex include
pigment granules = size, shape, density, distribution texture - fine, medium, coarse ovoid bodies and cortical fusi the presence of the medulla
37
what can be determined from the root if it is present (microscopically)
growth stage follicular material abnormalities
38
what type of microscopy should be used when deciding similarity between two hairs
comparison all instrumental parameters need to be the same on either side
39
what type of hair have the most discriminative value and why
head hairs as they tend to have more variation between individuals than other types
40
how should the secondary analysis of hair evidence be carried out
by a second examiner using a microscope that is blind to the conclusions from the first examiner
41
what type of analysis is done if microscopic analysis of hairs doesn't give sufficient evidence
SEM analysis elemental analysis fluorescence analysis DNA testing (not trace though)
42
what can hair analysis using SEM provide
higher resolution gives surface analysis giving physical damage, scales on hair
43
what 3 modes of SEM can give elemental analysis of hairs and the residues on it
secondary electron backscatter electron EDX
44
what are IR and Raman spectroscopy used for in hair analysis what is the name of the method used in the statistical analysis of IR and raman data
looking at hair treatments and chemical - can tell is hair is untreated telling which dyes may have been used upon comparisons with known samples chemometrics
45
what information can be gathered from the mass spectrum of a hair
atomic mass molecular formula molecular weight elemental presence chemical structure (from fragmentation patterns)
46
what can information gathered from the mass spectrometry in criminal investigations
substance identification tracking movements of people due to the substances present info on trace amounts of things
47
what type of species are detected by mass spectrometry
charged species, this is achieved by ionisation in the first stage of mass spec
48
what are 4 types of ionisation in mass spec
electron = hard, good for structural determination due to fragmentation = volatile species chemical = soft, good for molecular ion and M+H ion identification = volatile species electrospray = non volatile species = good for multiply charged ions MALDI (matrix assisted laser desorption ionisation) = highest mass - good for keratin identification = non volatile species
49
briefly explain ESI (electron spray ionisation)
analyte flows through a capillary into MS drawn into the mass analyser by a circular electrode a voltage is applied between capillary tip and circular electrode creates charged species that leave the capillary tip as a fine mist with a +ve or -ve charge
50
in mass spec what is DESI
desorption electrospray ionisation spray onto the surface of the sample creating charged species that go into the MS inlet doesn't destroy sample can detect surface contaminants
51
in mass spec what is LDESI
laser desorption electrospray ionisation an IR laser used to ablate the sample creating a cloud of neutral molecules cloud is then hit with electrospray = ionisation ions collected in MS no need for a matrix - can use live tissue
52
why is mass spec beneficial over IR and Raman but also why is it not?
good = ir and raman are likely to have a lot of noise to detect trace amounts bad = destructive of sample
53
what is MALDI
sample is mixed with a matrix without making chemical changes to the sample laser charges the matrix not the sample which passes charge onto analyte not destructive of sample - structure is maintained
54
what are the three types of analyser most using in mass spec for hair analysis
quadrupole = reproducible and low cost relatively, portable, low resolution and mass discrimination TOF - time of flight = best mass range, high accuracy, good LOD, measure speed of analyte, large instrument magnetic sector = best resolution, high accuracy, expensive and large
55
what is Tandem Mass Spectrometry
also called mass spectrometry/mass spectrometry, MS/MS or MS^2 only allows a particular ion of interest through to analyser do first mass analysis = parent ion is let through or selected then excite this species so fragmentation occurs = daughter ions and neutral fragments second mass analysis = then select the fragments you want to detect from daughter ions cna also go further and do it 3 times = MS^3 or MS/MS/MS
56
what are the two types of tandem mass spectrometer
tandem in space tandem in time
57
explain what is meant by a tandem in space mass spectrometer and why they are beneficial
the mass analysis stages (however many there is) are physically separated so they occur in different regions of the instrument different types of analyser can be used at each stage depending on your goal these instrument are a lot bigger than normal but have much greater mass spectra specificity
58
when is MS/MS often used
in analysis of drug concentration in hair as these are very low concentration compares to other matrices they are observed in e,g blood
59
why may two peak be seen for one element in the mass spectrum
due to different possible stable isotopes of that element the peak height is the ratio of these isotopes in the mixture
60
what is the name of the peak slightly above the M+ ion peak
MH+ ion peak the molecular ion peak plus a hydrogen atom - tends to happen in electron ionisation methods
61
what can looking at the isotope ratios of elements in the hair be used for
identifying the location an individual may have travelled based on the change in drinking water isotopes at different locations a lot of chemical elements have more than one natural abundance
62
what are the three main conclusions that can be drawn from microscopical hair analysis
association = questioned can't be distinguished from known inconclusive = questioned hair has some similarities and some differences but there are limiting factors cause complications exclusion = questioned hair has meaningful differences from known
63
what is the problem with hair evidence
hair can't be individualised on the basis of physical characteristics alone - microscopy can't determine if a hair come from a specific individual
64
why is hair evidence good
there is a large amount of morphological variation within individuals and between individuals which give discrimination potential of forensic hair comparisons
65
what factors strengthen and weaken the association conclusion
strengthen = distinctive cosmetic treatment abnormalities weaken short hairs incomplete hairs colourless not very pigmented
66
what is an example of something that can give an inconclusive conclusion
hairs being exposed to different environmental conditions e.g buried vs direct sunlight
67
how can the confidence in an exclusion conclusion be improved
by collecting many reference hairs from multiple sub areas in the person
68
what things affect the transfer of hair evidence
texture hair loss rate wear of hats washing artificial dying secondary transfers weather substrate type there are too many external principles to predict the number of hairs expected at a scene
69
what must a labs human hair reference collection include
different: ancestral groups cosmetic treatments diseases body locations damage types degradation types to be used for comparisons and should be updated regularly

Trace Evidence (16 decks)

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