Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

7BBFM128: Forensic Biology > Biological Search > Flashcards

Biological Search Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Biology flashcards Biology 101 flashcards
1
Q

Outline of lectures

A
  • Source vs activity
  • Detection of body fluids- semen & saliva & blood
  • Developing a forensic strategy in a sexual assault case
  • The future of BF ID- mRNA
  • Practical issues
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

LO

A
  • Appreciation of what make a good test
  • Details of blood, semen & saliva tests
  • Source v activity
  • Efficient forensic strategy setting
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Source Vs activity and developing a model

A

**Source vs activity **
* Allegation of anal rape
* Semen on anal swab- leave to jury…
* Take swabs from pyjamas to see if semen present as well

**Addressing activity- developing a model **
* Semen in vagina- what is probability that intercourse occurred
* Unknown- only that semen is present
* If intercourse with ejaculations, swabs taken rapidly  high probability of finding semen
* If semen inserted with syringe –> high probability of finding semen
* If only ejaculation into knickers –> very low probability of finding semen on high vaginal swab

**Addressing activity **
* A model to address activity:
o Probability of findings under prosecution proposition (Hp)
o Compared with…
o Probability of findings under defence proposition (Hd)

Forensic science aim to find the probability of findings IF activity occurred
Lawyers aim to find the probability of the activity occurring

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Some problems with activity levels statements

A
  • Defence proposition often not available (“no comment”)
    (Propositions addressed vastly influences answer)
  • Usually little or no data on activity available
  • Can be extremely complicated to evaluate
  • Should at least state that other explanations possible
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are some activity level statement examples?

A
  • BPA- scene & clothing
  • Semen on vaginal swab/ bedding/ condom
  • Semen on anal swab
  • Saliva on breast swab/ bra
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the different activity levels?

A
  • Offence- level 3
    o Forensic science doesn’t address this level, this is for the jury to decide
  • Activity- level 2
  • Source (body fluid)- level 1
  • Source (DNA)- sub level 1
  • Attributing DNA to body fluid- is profile from body fluid detected?
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is contained within semen?

A
  • Spermatozoa
  • Seminal plasma
  • Epithelia cells
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What does each sperm cells contain?

A
  • Spermatozoa (sperm cells)
    o Each sperm cell contains a nucleus and therefore each one can contribute to obtaining a DNA profile.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What attributes do sperm cells have that assist the forensic scientist?

A

 They have a characteristic appearance which enables them to be distinguished from vaginal cells.
 In addition, they are quite hardy and require extra chemical treatments to break them open to extract the DNA. This is due to disulphide bonds in their membrane which require Dithiothreitol (DTT) to crack them open.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Why is the attributes of semen important for obtaining a DNA profile

A

This is not only important for obtaining a DNA profile from semen, but is important for detecting sperm cells, by digesting away (with the use of Proteinase K) the more fragile vaginal cells. This in turn allows attribution of a DNA profile to semen rather than epithelial cells, as the latter should not withstand treatment with DTT – this is commonly known in the forensic world as a “ split pref”

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is seminal plasma?
What does it contain?
What volume is produced in one ejaculation?

A

o This is the liquid in which the sperm cells are carried. It contains high levels of acid phosphatase and choline, both important in the detection of semen (or more correctly seminal plasma).
o The volume produced in one ejaculation is about 3 to 5 ml (equating to about 160 to 1200 million sperm)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What speed is the ejaculation said to travel at?

A

28mph

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What can happen to epithelia cells with ejaculation?

A

o As it is propelled along the urethra there is a reasonable chance that a few epithelia cells that make up this tube get ripped from the lining
o This will be important if the offender has had a vasectomy
o Current DNA techniques can get a useful profile from very few cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How can semen be detected?
Give examples for each

A

**Visual **
* white light or UV- both not vert specific as semen can flouresce under UV but so can other things
**Chemical **
Detection of acid phosphatase (AP) or Choline (by formation of choline periodide crystals)
**Immunological **
- Prostate specific antigen (PSA) or semenogelin
- PSA not very specific, reacts with alot of things
- Semenogelin protein causes semin to jellify? Dont use this yet
Confirmation is by microscopic identification of spermatozoa

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the mechanism of semen detection via the AP test?
Tell me about the colour change

A
  • Highly water soluble
  • High amounts in semen
  • Acid phosphatase cuts phosphate off
  • Use brentamine which causes the alcohol and amine to react which causes a deep purple colour which shows the presence of semen due to the conjugation of the rings
  • Get a pink& brown colour with other conjugated phenols but not as strong a conjugation effect as that of semen
  • Acid phosphatase in low levels in vaginal secretions and high levels in semen
  • AP could be in low concentrations, even if semen, if not tested straight away. Then could get confused with vaginal levels of AP.so then would look at a slide to see if can see semen
  • Cant paint of spray on acid phosphatase after wetting with DH2O
  • In spray form it is highly carcinogenic so is done in a fume cupboard
  • Can also do the acid phosphatase test at the scene
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are the problems that could arise with the AP test?

A
  • False positive
  • False negative
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Give some examples of some false positives that could occur with the AP test?

A

o AP found in (low conc) in vaginal secretions
E.g., on vaginal swabs, crotch of panties- but speed of reaction helps
o Any chemical containing conjugated rings with hydroxyls
e.g., steroid creams, tea, faeces- but should spot abnormal colour

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Give some examplesof false negatives which could occur with the AP test

A

o Denaturation (heat), degradation in vagina, washing
o Semen doesn’t get washed out in washing machine, but the problem is finding it. Particularly the case with bedding
o Can find semen 3-4 and sometimes 7 days after ejaculation. However the chance of finding semen after 7 days is very low

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Tell me about the forensic semen scoring

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Semen on a vaginal slide

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Semen vaginal slide in the presence of yeast cells

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Some examples of semen and casework/ problems

A

** Exhibit types **
o Intimate swabs, clothing (knickers), condoms and pseudo condoms (not a condom but something that has been used as such), begging
* Case examples
o Children, animals (rare), time since intercourse (TSI)
** Problems **
o Lack of heads- vasectomy (no sperm heads), azoospermia, oligospermia
o Choline (Florence Iodine- choline periodide) may help- high AP and choline shows semen present
o Laundered items- semen transferred from one item of clothing to another item of clothing. If this was the case would expect sperm heads to be all over the clothing so would test multiple areas to show if from washing or action.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

How does the semen scoring change in regard to time since intercourse (TSI) in the following situations…
* Internal vaginal swab
* Internal anal swab
* Oral swab

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is saliva comprised of?

A
  • Liquid
  • Epithelial cells
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Tell me the following about the liquid portion of saliva:
* what does it consist of? What does this act as?
* How does it vary between individuals?

A

o This consists of water plus amylase this enzyme is the basis for the most common method of detection.
o The water serves to lubricate the mouth to enable swallowing.
o The amount of amylase varies between people, some having low levels and some virtually none. It also varies within one person from time to time and is even to reported to vary within one day.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What are the epithelial cells of saliva?

A

These are from the lining of the mouth and each cell contains DNA, and therefore are the source of material that can be profiled.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Tell me about the quantity of epithelial cells in saliva

A

The quantity of epithelial cells in saliva is highly variable as they are not intrinsic to saliva – they are present solely as a by-product of the movements of the tongue etc within the mouth.

28
Q

If the saliva sample was taken immediately after drinking, what may it contain?
What does this provide a relationship explanation for?

A

o If a saliva sample were taken immediately after drinking it may contain little cellular material or amylase.
o It should be obvious from the above that the relationship between the quantity of amylase in a stain and the quantity of cellular material (and therefore DNA) is not necessarily linked.

29
Q

What may a saliva stain contain a lot of? How does this vary? Why could this cause a problem?

A

A stain may contain a lot of amylases but few cells and a stain from a different person may contain almost no amylase but lots of cells. This causes a problem for attributing any DNA profile obtained to saliva.

30
Q

How can saliva be detected and examples for each?

A

Visual
Light sources- not specific
Chemical-detection of amylase
-Blue dye bound to starch- particulate appearance
-Phadebase paper, filter paper with phadebas on
-Starch digested releasing blue dye- homogenous appearance
**No confirmatory test available currently for saliva **

31
Q

What are some issues that can arise with saliva detection?

A
  • Amylase found in other body fluids and food stuffs especially seed based, fungi, some detergents (dish washing)
  • Test not as good as AP but better than nothing
  • Vaginal and faecal amylase
    o False positive if using phadebas on vaginal swab, would go straight for DNA
  • Amount of amylase varies between individuals
  • All these factors contribute to attribution issues
32
Q

How is saliva detection carried out in a lab?

A
  • Place phadebas paper on item
  • Wet it
  • Leave for 40 minutes for a good result
  • Dilutes DNA out as been exposed to water for 40 minutes
33
Q

Strategy setting- alleged rape, scenario 1

A
  • Police request- urgently identify the offender by searching the NDNAD

Scenario:
o Women walking home after night out
o Dragged into alley and vaginally raped by unknown assailant
o Anal penetration attempted
o Both breasts licked
o Victim threatened with knife and punched repeatedly
o She reports to police and is examined at SARC within 24 hours
* You have one assistant who takes 2 hours to examine one item
* Success rate for DNA profiling of semen is 85%, success rate of saliva is 35%

  • Exhibits available to me:
    o Knickers, dress, bra, blouse, jacket, shoes
    o EVS, LVS, HVS, endo-cervical swab
    o External and internal anal swab
    o Left and right breast swabs
  • What will you examine?
    o HVS - (but would have to know if and where ejaculated)
    o One breast swab
    o Knickers potentially
34
Q

Strategy setting- alleged rape, scenario 2

A
  • Police request- urgently identify the offender by searching the NDNAD

Scenario
o Women walking home
o Dragged into alley and raped by unknown
o Penetration attempted
o Both breasts licked
o Victim threatened with knife and repeatedly punched
o Traumatised and goes home and doesn’t mention for 3 days. Goes to SARC 5 days later

  • You have one assistant who takes 2 hours to examine one item
  • Success rate for DNA profiling of semen is 85%, success rate of saliva is 35%
  • Chance of semen remaining more than 3 days is 10-20%
  • Exhibits available:
    o Knickers, dress, bra, blouse, jacket, shoes
    o EVS, LVS, HVS, endo-cervical swab
    o External and internal anal swab
    o Left and right breast swabs
  • What will you examine?
    o HVS- not the best because low semen levels after days
    o Breast swabs but would have showered
    o Has she washed clothing?
    o Knickers is the best item to go for in this case
35
Q

Strategy setting- alleged rape, scenario 3

A
  • Police request- is there evidence to support the victims account?

Scenario
o Women meets man at nightclub and leaves with him
o Dragged in alley and raped
o Penetration attemoted and breasts licked
o Immediately reports within 24 hours and tested
o Suspect arrested and charged with rape
o He only states that they have consensual vaginal intercourse

  • Exhibits given:
    o Knickers, dress, bra, blouse, jacket, shoes
    o EVS, LVS, HVS, endo-cervical swab
    o External and internal anal swab
    o Left and right breast swabs
  • What will you examine?
    o Breast swabs (look for difference in stories)
  • The custody time limit clock is ticking…24 hours generally sometimes 36 in custody, sometimes can add another 12 if go via another route- clock starts when they are arrested
36
Q

What are some componenets found in blood?

A
  • RBC
  • White blood cells aka. Leukocytes
  • Plasma
37
Q

What are red blood cells?

A

These cells carry oxygen around the body, have no nucleus and therefore no DNA.

38
Q

What gives RBC their red colour?
How does this help in forensics?

A

o The haemoglobin which transports the oxygen gives RBC their red colour and it is this that enables bloodstains to be easily detected on most surfaces and colours.
o The actual shade of red, combined with the textual appearance of the stain enables the experienced forensic scientist to discriminate blood stains form most other stains, especially tomato sauce! (That’s ketchup for our American cousins).

39
Q

What can blood be detected with?
Is this test human specific?

A

o When combined with a strong positive KM reaction, the likelihood of the stain being blood is near to certainty.
o Note that the appearance and KM reaction will not distinguish human from animal blood.

40
Q

What activity does haemoglobin also have?
Tell me about this

A

o The haemoglobin also has a peroxidase like activity – the presence of haemoglobin will oxidise suitable substrates when a source of oxygen in the form of peroxide is present. This is the basis of the KM test.

41
Q

What is RBC role in DNA profiling?

A

As RBC have no DNA, they play no part in DNA profiling – in fact haemoglobin is known to inhibit the PCR reaction and must be removed during extraction and clean up. This is probably because Mg2+ is a critical co-factor for PCR and is bound up by the haemoglobin in a similar fashion to iron.

42
Q

What is the cell in blood that is used for DNA profiling?

A

White blood cells
These have DNA and therefore are the blood component that is profiled.

43
Q

How many leukocytes are there per µl?

A

Their number ranges from approximately 4,500 to 10,000 per ul.

44
Q

What is the purpose of leukocytes?

A

o Their purpose is to fight infection – if you have a cold their numbers will rise to fight the virus, if you are healthy the numbers will fall to your normal baseline.

45
Q

How can variations in leukocytes effect DNA profiling?

A

This variation may explain why very small bloodstains sometimes will give a DNA profile and sometime will not – it may depend on whether the donor had a mild infection.

46
Q

How may a persons blood DNA profile be altered?
How ever, why is this unlikely to be an issue in a forensic examination?

A

Potentially a person’s blood DNA profile could be altered by a blood transfusion or medical intervention where they have a lymphocyte transplant such from a bone marrow donor.

This is extremely unlikely to be an issue in a forensic examination as
 blood will have had white blood cells removed before transfusion to avoid histocompatibility problems.
 it is unlikely that people with an illness requiring bone transplants would be either a suspect or victim in a forensic case

47
Q

What is blood plasma?
Tell me about it

A

This is the liquid part of blood and plays no part in the identification of bloodstains, apart from its appearance in retracted colts as part of a blood pattern assessment. serum is plasma with the clotting agents removed.

48
Q

How can blood be detected and give some examples?

A

Visual and chemical
-Chemical could be luminol
White light- in lab
-Good overhead lightinf, fibre optic and ring lights, LP microscopy, good eyesight, and lack of colour blindness
White light- at scene
-Torch with stong even illumination- Crimelite
-Other wavelengths- any different light source may show “stains” not seen easily with the eye- but not as specific as not in humans normal experience (i.e., white light vs IR later)
-Kastle-meyer (KM): turns bright pink colour
-Leucomalachite green blood test (LMG): turns green
-Hemastix: turns green colour to blood (but also other things)
-Luminol: turns bluish-white light when peroxidase is added

49
Q

The Chemical methods of visualising blood

A
50
Q

What is the mechanism behind the KM reaction (1903)?

A
51
Q

The KM test can lead to false positive and negatives, tell me what these could be

A

**KM false positives **
* Presumptive test- non-blood substances may give positive result
* Plant peroxidase, rust, mould, bacteria, faeces
* Typically, they do not look like blood, caution with rust
* Chemical oxidants (e.g., cleaning agents in a sink trap)- colour change without addition of peroxide

KM false negatives
* False negatives- e.g., if blood heated on radiator, destroys peroxidase activity, old or washed/ dilute blood may not give KM positive reaction

52
Q

What are the different ways in which the KM test can be carried out? What test is similar?

A
  • KM reagent a sensitivity of approximately 1 in 10,000 dilutions
  • Spot test- filter paper rubbed onto stain; reagents added to paper
    * Direct test- part of stain added to paper and reagents added (added reagents in turn to observe colour, when final added then should have instantaneous colour change)
  • General screen- when searching for non-visible bloodstaining, consider LPM search beforehand as screening may disrupt small bloodstains
53
Q

Some aspects of laboratory examination of blood

A
  • Low power microscopy can be up to x96
  • Can have a foot pedal which takes a photo of what can be seen
  • Double gloves, lab coat, hair mob, beard cap, masks, clean bench and everything to use before exhibit is out
54
Q

Tell me about the Hemastix test?

A
  • Simple and sensitive test of Prescence of blood
  • Peroxidase activity of haemoglobin (Hb)
    o Catalyses reaction of di-isopropyl benzene Di hydroperoxide and 3,3’, 5,5’-tetramethylbenzidine
  • Wet pad, apply to bloodstain, pad goes green
  • Sensitivity of 1 in 10,000 dilutions
  • Less specific than KM- a positive reaction indicates a possible presence of blood
55
Q

How does the immunologicla test of blood work?

A
  • Simple and sensitive test for presence of human blood
  • Antibodies raised to human Hb
  • Works like a covid LF test
  • Issues of risks around the interpretation
56
Q

How does the luminol test work?

A
  • Sensitivity claimed for dilution of 1 in 300,000 to a million (not seen in practice)
  • Peroxidase activity of haemoglobin catalyses reaction
  • 3-aminophthalhydrazide (luminol) is oxidised in alkali solution to 3-aminophthalate
  • In oxidising conditions, luminol produces free nitrogen and light is emitted
  • Reach is with hematin- oxidised Hb, hence old blood stains work better
57
Q

What are some formulations for luminol?

A

Several formulations- Grodsky, Weber, BlueStar

o For “invisible” blood- mostly scene for signs of clean up
o Most sensitive and least specific tests
o Sprayed in (ideally) total darkness & reaction is brief (seconds to mins)
o Recording a problem- interpretation even more so

58
Q

How does the infra-red detection of blood work?

A
  • Blood absorbs IR- appears dark
  • Many fabrics do not absorb IR- appear light
  • Blood appears, dark on light
59
Q

What are the pros to IR detection of blood?

A
  • Non-destructive
  • Instantaneous
  • Visualises BPA
  • LOD - <1m, typically 1 to 3mm
60
Q

What are the cons to IR detection of blood?

A
  • Fabric only- not all fabric detects IR
  • Not blood specific
  • Misses some blood
  • Equipment can be costly
61
Q

Blood- Case examples

A
  • Exhibit types
    o Clothing, weapons
    o Samples from scenes, vehicles
    o Hand and penile swabs
  • Case examples
    o Finger-marks in blood,
    o Distribution may be sufficient
  • Problems
    o Animal blood, false positives
62
Q

Attributing DNA to body fluids

A
  • Strong stain, plenty of DNA
    o Expect a profile
  • Strong stain on contaminated substrate
    o Expect a mixture
  • Weak stain, minimal DNA
    o Expect no profile
  • Weak stain on contaminated substrate
    o Single profile, but not from stain
  • For blood and semen- have measure of strength
    o Colour and sperm score
  • For saliva- have weak/ variable measure of DNA
    o As cells are not intrinsic to saliva
63
Q

What is the future of body fluid identification?

A
64
Q

What are the pros to using mRNA to identify body fluids?

A
  • Potentially highly sensitive- based on PCR
  • Less subjective (compared with assessing KM result)
  • Can be incorporated into current DNA testing
  • For some body fluid types there is currently no detection method e.g., vaginal secretions, menstrual blood
65
Q

What are the cons to using mRNA to identify body fluids?

A
  • Need to develop specific PCR regimes
  • Mixtures difficult to deal with- unable to link mRNA with a particular DNA profile
  • Quantity of mRNA expressed can vary within one individual e.g., saliva
  • Requires sophisticated PCR work to give simple result (“is it blood?”)
  • Relatively expensive DNA test vs KM test
  • Tests are still not 100% specific
  • In this country, not yet available

7BBFM128: Forensic Biology (19 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions