Hairs Flashcards
What has been understood about microscopical hair examinations sine 1873?
- it has been understood since 1873 that microscopical hair examinations ALONE do not result in individualisation (cannot be confident hair comes from individual)
- it cannot be said that any questioned hair comes from a specific individual based upon microscopy alone - link DNA and there is an increased chance of doing this
What are the six reasons as to why hair is a great form of trace evidence?
- it is found on all humans and other mammals so good chance left behind as TE
- it is constantly being produced and shed in their immediate environments
- it is easily overlooked by criminals involved in nefarious activities (they remember fingerprints etc.
- it is highly stable resisting both physical and chemical degradation (persists for a long time, after 1000 of years potentially)
- it is readily transferred from one person/object to another person/object
- hairs from different individuals can be distinguished from each other and with DNA testing (can do nuclear DNA testing if has follicle)
What mistake to forensic labs make when examining hair?
- stop after DNA testing but there is more to hair than this
- can provide investigative leads or help with the reconstruction of events in contention
- and about where perpetrator has moved in past (microscopic and elemental analysis)
What are hairs composed of?
- hairs are composed primarily of protein (keratins)
- remarkably stable tissues - chemically and physically (can persist almost unchanged at ultrastructural level as keratin is extremely robust)
Why is it not practical to differentiate hairs using chemical techniques?
What must be used instead?
- all hairs have the same chemistry
- elemental analysis and spectroscopic techniques
What can be done when looking at isotope ratio of elements in hair?
- looking at isotope ratios of elements in the hair using isotope ratio mass spec
- can be used to identify locations where an individual may have travelled based on changes in drinking water isotopes in different locations
What are three types of hairs in humans?
What is type used in forensic analysis and why?
1 - lanugo - hairs are formed in uterus and are fine and unpigmented
- shed before or shortly after birth so rarely a relevant form of TE unless talking about unborn/newborn children
2 - vellus - fine short unpigmented/lightly coloured hairs present on almost all skin surfaces (forehead, nose, ears, bald scalp)
- not hands/palms of feet
3 - terminal - typical hairs macroscopically visible on children and adults
- primary: head, eyelash and eyebrow
- secondary: pubic, underarm and beard
- forensic analysis of hairs generally restricted to the terminal ones (these are what have value in court):
- need a reasonable chunk of hair to be able to analyse it - vellus too short
- most commonly recovered are head and pubic
What are three main histological layers of hair?
What are two other components of hair?
- cuticle (outermost layer):
- largely responsible for chemical resistance of hair
- useful and has probative value
- cortex (main bulk of hair):
- largely responsible for mechanical properties of hair (flexibility, strength, floppibility)
- contains most of pigment granules giving hair a colour
- medulla - innermost layer of hair shaft
- not very well studied/understood
- not present in all hairs (so can use this to discriminate between two samples)
- has slight pigmentation but bulk of pigmentation from cortex
- cell membrane complex (CMC) - bonds all cells together
- layer of cells found at interface between cuticle and cortex
- has slightly different mechanical properties
- rarely considered in forensic perspective
- follicle - where hair grows from and changes size and shape throughout the hair cycle
- where most likely to have any recoverable DNA
- follicle not always present
What is the hair cycle?
What can be said about this cycle between individuals?
- anagen - active growing phase of hair extending progressively from the follicle root outwards from skin (85-90% of human head hairs)
- catagen - transition phase when growth slows and eventually stops
- hard to judge this phase
- telogen - resting phase when minimal force is required to remove hair and natural shedding likely to occur (exigent) (10-15% of human head hairs)
- every individual hair progresses through this cycle at a rate which depends on hair type and individuals
What does hair shedding depend on?
- 30-100 hairs shed every day depending on huge range of environmental factors (how much brush hair, if we wear hat)
What is average that hair grows a month?
- around 1cm a month depending on ancestral groups and age
- Asian - fastest
- European - middle
- African - slowest
What happens when hair turns grey?
What is this use in TE?
- it doesn’t turn grey the pigment stops being produced giving the appearance of white/grey
- tip is pigmented but near scalp not
- different points on same strand of hair may differ in colour
- this gives us some discriminative value
What are two methods of collection?
- forceps: for individual hairs forceps can be used to isolate and collect
- be careful with damaging hairs as too much pressure can ruin hair and this is bad as we are interested in the morphology of hair
- tape lift: most efficient when collecting hairs from large surfaces
- solves problems with forceps but is less precise
What must be done during collection of known samples?
- need to collect a representative sample due to inherent variation
- ENFSI recommendations suggest collecting 20 hairs from 5 head regions and package them separately in order to give you enough variation
- collect through combination of plucking (high pressure) and combing (low pressure)
- some more likely to get follicle and some shape is going to be different and some will be at different growth phases
Define the seven step analytical workflow for hairs?
- gross examination, recovery, and collection
- preliminary evaluation of physical characteristics
- microscopic techniques
(a lot of labs stop here – but there is a lot more you can get from hair)
- DNA
- SEM (Very occasionally TEM)
- spectroscopic techniques - IR & raman
- chromatographic techniques & mass spectrometry
What microscopic techniques can be used in forensic investigation of hair?
- main ones: stereoscopic, comparison, polarised, reflected light and brightfield
- if something more useful to collect: fluorescence and SEM
- very unlikely - thermal
What are four morphological characteristics of hair observed at macroscopic level?
What is used to observe these?
1 - macroscopic colour - colourless, blonde, red, brown, black (may use coloured backgrounds to provide contrast so can assess colour)
2 - length - measured in absolute units e.g. mm
3 - general contour and curliness - straight, wavy, curly, kinked
4 - approximate diameter - thin, medium, thick
- stereoscopic microscope (can use at scene to aid recovery)
What microscope is used after stereoscopic one?
What must be done when comparing questioned and known hairs?
What 9 features are evaluated in this step? and why?
- hairs mounted in appropriate medium for examination with compound light microscope with polarising filters (these allow for more info)
- questioned and known hairs should be in same media to provide equivalent contrast
- to provide more discriminatory value between samples:
1 - colour (colourless, blonde, red, brown, black)
2 - cross sectional shape (round, oval, flattening
3 - biological damage (insect bites, fungal, bacterial activity)
4 - cosmetic treatments (bleached, dyed)
5 - shaft irregularities (buckling, twisting)
6 - adhering material (blood, nots, particles, residues)
7 - thickness range (um)
8 - general damage (split, frayed, broken, crushed, burnt (burnt allows more discriminatory value)
9 - non-root morphologies (rounded, cut, broken)
