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Intro To Forensics > Bio Fluids & DNA > Flashcards

Bio Fluids & DNA Flashcards

1
Q

The identification of blood typically employs…

A

presumptive tests & a confirmatory test

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2
Q

What supports the identification of blood?

A

Visual observation
Positive chemical presumptive tests
Confirmatory test

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3
Q

Catalytic tests employ…

A

the chemical oxidation of a chromogenic substance

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4
Q

Two most commonly used presumptive tests today

A

Kastle-Meyer & Hemastix

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5
Q

Phenolphthalein

A

Produces a bright pink color when used in testing suspected blood

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6
Q

Luminol

A

Produces light when reacting with blood

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7
Q

Chromogenic substances produce what when reacting with a material of interest?

A

A colored substance

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8
Q

The starch-iodine test is __ for saliva.

A

Presumptive

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9
Q

SAP can be found….

A

In semen, breast milk, saliva, and other fluids

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10
Q

A presumptive test for blood can result in a false positive from…

A

Chemical oxidants
Materials of animal origin
Plant material
Vegetable peroxidases

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11
Q

What characteristic does an enzyme need to be useful for PCR?

A

Withstand extreme heat

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12
Q

Who do you inherit your mitochondrial DNA from?

A

Your mother

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13
Q

A heterozygous person has how many peaks a particular locus?

A

Two

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14
Q

Presumptive Test

A

Test which indicates the presence of a compound of interest
-High sensitivity, moderate selectivity
-Material should be examined further

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15
Q

Confirmatory Test

A

Test or tests which positively identify the material
-Moderate sensitivity, high selectivity

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16
Q

The 5 test results

A

False positive
False negative
True positive
True negative
Inconclusive

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17
Q

Presumptive testing method steps

A
  1. Sample the stain (swab or filter)
  2. Apply the reagents
  3. Document results
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18
Q

Kastle-Meyer/Phenolphthalein Test

A

-Use on visible stains
-Reagent is phenolphthalein in an alkaline solution
-Peroxide will react with the iron in hemoglobin (if blood truly is present)

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19
Q

Leucomalachite Green

A

-Use in visible stains
-AKA McPhail’s reagent
-Add hydrogen peroxide to reagent + hemoglobin

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20
Q

Test Sticks

A

-Use on visible stains
-Uses tetramethylbenzidine as the reactive agent
-Touch the lad to a moistened stain; produces blue-green color with a positive result

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21
Q

Leucocrystal Violet

A

-Use on low visibility stains for enhancement
-Reacts with hemoglobin to turn purple/black

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22
Q

Luminous Tests

A

-Use for detection
-Luminol as reactant, makes blood glow (glow is very weak)
-Bluestar as another reactant, produces stronger glow
-Hemascein as reactant, makes blood fluoresce (weaker glow, requires filter)

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23
Q

Which oxidizers most commonly cause false positives?

A

-Bleach
-Copper & Iron
-Plant fluids
-Air (ozone)

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24
Q

Teichman & Takayama Tests

A

-Form hemochromogen crystals by reacting to iron in blood

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25
Q

Immunoassay Test

A

-ABAcard Hematrace
-Hexagon OBT1
-Like a “covid test” but for blood

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26
Q

Karl Landsteiner

A

-Wanted to figure out why some blood transfusions didn’t work
-Discovered/named main blood types

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27
Q

What are immunoassays used for?

A

-Drugs
-Hormones (Pregnancy tests)
-Cholesterol levels
-Fluid Identification

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28
Q

Ouchterlony precipitin test

A

-Different species’ antibodies and questioned blood
-Antibodies and antigens diffuse through gel, leaving a visible line

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29
Q

OBT1 & ABA Hematrace immunoassays

A

Confirm the presence of blood/tell if it’s human or not

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30
Q

Acid Phosphatase (AP)

A

Secreted in large quantities by the prostate and other organs
-Brentamine Fast Blue B is used to identify it (effective on men with low/no spent counts)

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31
Q

Time to detect sperm heads?

A

V: 7 days
A: 2-4 days
Mouth: 24 hours

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32
Q

Time to detect tailed sperm?

A

V: <26 hours
Everything else: <5 hours

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33
Q

Being a serologist requires

A

At least a bachelor’s degree of science

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34
Q

Serology is a dying field because

A

DNA analysts typically perform serological duties themselves

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35
Q

Fibrin

A

Protein that is formed after injury to form blood clots

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36
Q

The solid part of blood is made up of

A

Red and white blood cells, and platelets

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37
Q

Main difference between plasma and serum?

A

Serum has no clotting factors, plasma does

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38
Q

Luminol characteristics

A

-Lasts for about 30 seconds
-Can be performed multiple times
-Numerous false positives are common

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39
Q

Bluestar Forensic characteristics

A

-Lasts longer
-Environment does not have to be completely dark
-Common for false positives, but not as often as luminol

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40
Q

Fluorescein characteristics

A

-Requires an ALS to view properly
-Can be used in a heavily lit room

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41
Q

Electrophoresis Method

A

Electrically charged gel used to determine species origin of an unknown sample

42
Q

There is no test kit for _____

A

Vaginal fluids

43
Q

Types of presumptive tests for urine

A

ALS
Jaffe Test
SEM-EDX

44
Q

Touch DNA

A

DNA that is left behind by an individual when they come into contact with an item

45
Q

system of linked databases that start at the local level and move through the state level to the national level

A

CODIS

46
Q

Homologous:

A

pair of chromosomes

47
Q

Locus/Loci:

A

Location of a sequence on a chromosome

48
Q

Alleles:

A

different possible sequences at a locus

49
Q

Homozygous:

A

Two identical alleles at one locus

50
Q

Heterozygous:

A

Two different alleles at one locus

51
Q

DNA is found in any….

A

nucleated cell

52
Q

Examples of nucleated cells

A

White blood cells
Epithelial cells
Bone Marrow
Hair roots
Tooth pulp
Spermatozoa

53
Q

How might we collect DNA samples?

A

Swabbing:
Stain
Orifice
Tool
Buccal swab;

Cut sample:
Clothing
Bedding

54
Q

We must keep samples ____

A

Dry & Cold

55
Q

What do we do during the extraction stage?

A

Break down proteins
Remove cellular debris
Remove clean DNA

56
Q

No two people have ____ genomes

A

identical

57
Q

Variation in ____ is stable

A

non-coding areas

58
Q

Sir Alec Jeffreys

A

geneticist who figured out how to target areas of the genome with great variability and individualize the source of biological material

59
Q

More bands=

A

More power

60
Q

Gel Electrophoresis requires

A

large amounts of high quality DNA

61
Q

STR Process

A

Mix labeled primers with sample
Amplify via PCR
Use electrophoresis to separate the fragments
Compare the fragment sizes to a ladder of known alleles for each locus
Report the fragments as a profile
Compare the profile to a sample or database

62
Q

Strengths of STR

A

Looks at specific loci
1 bp resolution
Fast
Can be multiplexed
Can be databased
Done by a robot rather than a human

63
Q

Most of the tests used at crime scenes are presumptive tests, which have a certain likelihood of false positives. Why is this OK?

A

Even if we accidentally collect non-blood material, confirmatory tests conducted at the lab will collect it.

64
Q

What are chemical markers?

A

Antigens

65
Q

Individual cells can have ___ antigens

A

Many

66
Q

What is the relationship between antigens and antibodies?

A

Antibodies recognize and attach to highly specific types of antigens

67
Q

We are using the OBT1 to determine if a blood sample is human or not. The control area of the test does not change color.

Which of the following statements about this test is true?

A

The mobile antibodies did not bind to the immobile antibodies in the control zone.

68
Q

Which is the appropriate choice for initial survey for and detection of semen stains?

A

Visual detection with ALS

69
Q

On their own, either the acid phosphatase or prostate-specific antigen test would be considered a ___ test for semen

A

presumptive

70
Q

Which tests can be used to reliably identify saliva?

A

Phadebas
RSID Immunoassay
Starch Iodine Test

71
Q

The two best ways to detect the presence of urine is the use of the ____ or the presence of ____

A

ALS; odor

72
Q

Bleach

A

Oxidizes heme-reactive blood tests, causing a false positive

73
Q

Hematrace

A

Immunoassay that reacts to proteins on the outside of the red blood cells

74
Q

Takayama test

A

Confirmatory test which produces hemochromogen crystals

75
Q

Hemastix

A

A self contained test pad on a plastic strip, used with visible stains

76
Q

McPhail’s Reagent

A

Reacts with the iron in the hemoglobin to turn a suspected visible or faint blood stain green

77
Q

What does the PCR process do?

A

Makes a BUNCH of copies of something

78
Q

Microvariant

A

An allele with an incomplete repeat

79
Q

Capillary Electrophoresis

A

Thin tube packed with silica beads that detects individual base pairs in fragments

80
Q

Multiplexing

A

Sorts all loci at once
Loci with similar length alleles are given a unique color

81
Q

If we have an identification….

A

All the known’s allele’s are present in the unknown
There are no extra alleles in the unknown

82
Q

Siblings share ____ of alleles

A

about 50%

83
Q

Can nuclear DNA be extracted from the red blood cells in a blood stain?

A

No, we need to use white blood cells for that (or mitochondrial DNA)

84
Q

You inherit mitochondria ____

A

Maternally

85
Q

Why is it important for forensics that in double stranded DNA, we always see the specific pairs A-T and G-C stuck together?

A

If we have one half of the double helix, we can reconstruct the other perfectly

86
Q

There are a maximum of two alleles that can be found at any given locus?

A

No, many possible

87
Q

The most common DNA reference sample is

A

buccal swab

88
Q

Blood is ______ before collection

A

ALWAYS allowed to dry

89
Q

DNA extraction protocol

A

Lyse cells open
Treat with proteinase
Remove DNA for analysis

90
Q

Everyone has their own genetic footprint except

A

Monozygotic identical twins

91
Q

We name VNTR alleles by….

A

how much they repeat

92
Q

What are the key reasons that PCR amplification is routinely performed on all samples for modern DNA analysis?

A

It generates a lot of identical copies of our sample, making electrophoresis results much easier to read
It only copies the loci that we care about, cleaning up a lot of background noise
It can help compensate for damaged or degraded DNA samples by making copies of intact segments

93
Q

What is the main difference between traditional genetic fingerprinting and STR analysis?

A

STR analysis compares the exact size of DNA fragments at specific loci instead of chopping the entire genome into fragments

94
Q

Peaks in an electropherogram represent….

A

the alleles present

95
Q

How do we calculate the likelihood of homozygous alleles?

A

the frequency of the allele squared

96
Q

How do we calculate the likelihood of heterozygous alleles?

A

2 times the frequencies of each allele

97
Q

How do we calculate overall likelihood?

A

multiply each likelihood together

98
Q

CODIS steps

A

Amplify sample using PCR
Generate an STR profile
Verify that the profile has results at a minimum of 8 loci
Submit your data against the CODIS database
Have a DNA analyst compare the returned profile against the profile from the evidence
If the DNA analysts concludes they are from the same source, obtain a warrant for the CODIS result’s personal information.

99
Q

Y-STR profiles are passed through….

A

father to son, and his son, and all biological sons (no daughters)

100
Q

Carol and Cooper are first cousins who married. Imagine that in addition to Dot, they have a son named Daniel. How would Daniel’s genetics compare to Ben and Bob?

A

The three men would have the same mtDNA profiles and the same Y-STR profiles

Intro To Forensics (19 decks)

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