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Forensic Biological Evidence > M4 > Flashcards

M4 Flashcards

1
Q

4 bases projecting from the backbone of DNA that consists 5 Carbon Sugars (ribose) and phosphates that form the backbone of DNA

A

A - adenine G- guanine, T - thymine, C - cytosine

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2
Q

DNA is a polymer consisting of monomer units known as

A

nucleotides

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3
Q

Nucleotides consist of an organic base consisting of

A

A 5 carbon sugar (ribose) and phosphate to form the backbone of DNA.

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4
Q

DNA regulates cell activity by

A

specifying how to make proteins

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5
Q

Some proteins are structural and others function as

A

enzymes

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6
Q

Genetic differences among people that enable them to be distinguished are called

A

Genetic Polymorphisms

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7
Q

Prior to DNA typing analysis, forensic scientists used

A

proteins and enzymes as genetic markers to try to individualize biological evidence

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8
Q

The entire complement/entire set of DNA in one cell is called the

A

genome

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9
Q

Human DNA has ~3.5 Billion

A

base pairs (bp)

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10
Q

The base sequence in the coding portions of the DNA is known as the

A

genetic code

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11
Q

The majority of DNA is

A

Non-CODING

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12
Q

Non-Coding DNA regions contain

A

Tandemly Repeated Sequences (STR)

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13
Q

DNA Human Identity Testing is used in

A

Forensic cases - Matching suspect w/evidence
Paternity testing - Identifying Father
Historical investigations
Missing persons investigations
Mass disasters - putting pieces back together
Military DNA “dog tag”
Convicted felon DNA
Emigration & Human Trafficking

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14
Q

The DNA Profiling Process involves

A

DNA Extraction
DNA Quantitation
PCR Amplification
Separation & Detection
Interpretation

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15
Q

Steps in Nucleic Acid Extraction

A
  1. Cell & Tissue Disruption
  2. Lysis of cellular & organelle membranes
  3. Removal of protein & cytoplasmic constituents
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16
Q

Cell & Tissue Disruption

A

a method in which the outer boundary or cell membrane is broken down in order to release cellular materials such as DNA

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17
Q

Used in the process of of nucleic acid extraction to break down the protein component of the cell membrane and allow access to the DNA & RNA

A

Proteinase K

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18
Q

Mechanical methods of cell & tissue disruption

A

Grind bones & teeth
Decalcification with Ethylenediaminetetraacetic acid (EDTA)

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19
Q

Lysis of Cellular & Organelle Membranes

A

Release DNA from nuclei & mitochondria

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20
Q

Lysis

A

the disintegration of a cell by rupture of the cell wall or membrane

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21
Q

Lysis buffer

A

buffer solution used for the purpose of breaking open cells for use in molecular biology

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22
Q

Lysis buffer consists of

A
  1. Detergents (SDS) - destroys membranes
  2. Buffer (Tris) - maintain pH, avoid enzyme degradation by Dnase
  3. High salt concentrations (guanidinium salts) - Dissociate histones from DNA
  4. Reducing agents (DTT) - Inhibit oxidation that can damage DNA
  5. Chelating agents - capture divalent metal ions that are Dnase cofactors
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23
Q

Histones

A

a protein that provides structural support for a chromosome

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24
Q

Cytoplasmic components & proteins interfere with

A

DNA isolation & need to be removed from the sample in DNA extraction

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25
Q

Methods to remove dissolved proteins

A

Phenol-chloroform-isoamyl mixtures
DNA binding to a solid matrix - wash away contaminants

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26
Q

Methods of Extraction in the
3. Removal of Protein & Cytoplasmic Constituents

A

a) Solid phase-based (Silica) Extraction
b) Differential Lysis Extraction
c) Application of Automation & Robotic platforms

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27
Q

Removal of Protein & Cytoplasmic Constituents Method based on Sample Type as appropriate for the laboratory

A

1 Selection of suitable isolation method for sample type & condition
2. Pre-extraction cell separation (e.g., cell sorting, laser capture microdissection)
3. Pre-extraction processing (e.g., soak grinding, demineralization)
4. Post-extraction processing (e.g., filtration, concentration, preservation conditions)
5. Non-extraction direct amplification approaches

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28
Q

3 Removal of Protein & Cytoplasmic
a) Silica-based Extraction

A
  • DNA is reversibly absorbed by silica in the presence of chaotropic salts
  • Chaotropic salts disrupt hydrogen bonds
    • causes nucleic acids to
      become hydrophobic
    • Phosphate groups available
      to interact w/silica
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29
Q

Silica

A

is the stationary phase to which DNA binds

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30
Q

Removal of Protein & Cytoplasmic Constituents
DNA Absorption onto Silica

A
  • Occurs in the presence of chaotropic agents
  • Double-stranded DNA is absorbed
  • Cellular contaminants DO NOT BIND
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31
Q

Removal of Protein & Cytoplasmic Constituents
Washing

A
  • Removes chaotropic salts & contaminants
  • Certain solvents (EtOH) will not affect DNA’s interaction with silica
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32
Q

Removal of Protein & Cytoplasmic Constituents
Elution of DNA

A

DNA is eluted by rehydration w/low salt solutions

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33
Q

Elution of DNA

A

generally a process of extracting one material from another by washing with a solvent

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34
Q
  1. Removal of Protein & Cytoplasmic Constituents Steps
A
  1. Cell Lysis & Protein Digestion
  2. DNA Absorption onto Silica
  3. Washing
  4. Elution of DNA
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35
Q

Removal of Protein & Cytoplasmic Constituents
c) Differential Extraction

A

THE GOAL of the procedure is to separate a sample that would otherwise generate a mixed DNA profile into 2 separate DNA profiles by enriching for the DNA from the MALE sperm donor (e.g., collected in a sexual assault case) in the sperm fraction and enriching for the DNA from the donor of the non-sperm cell fraction.

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36
Q

In Differential Extraction sperm and non-sperm cells are lysed at separate times based on

A

the properties of the different cell membranes. Sperm and non-sperm cell fraction can be isolated.

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37
Q

In Differential Extraction is useful for extracting DNA in

A

Sexual assault cases
* usually mixtures of spermatozoa from MALES & epithelial cells from FEMALES
* mixed DNA profiles complicate data interpretation

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38
Q

In Differential Extraction lyse non-sperm cells with

A

Proteinase K
* Sperm cells are resistant
—Membranes contain proteins crosslinked by disulfide bonds

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39
Q

Differential Extraction Method includes

A
  • Centrifuge tube
  • Lyse sperm cells with Proteinase K & DTT
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40
Q

Dithiothreitol (DTT)

A

is a reducing agent that breaks down the protein disulphide bridges that make up the sperm nuclear membrane.

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41
Q

Sperm nuclei are impervious to digestion without

A

DTT

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42
Q

In Differential Extraction Method 1 sample generates

A

2 fractions of DNA
* Sperm & non-sperm cell DNA may not be completely separated

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43
Q
  1. Removal of Protein & Cytoplasmic Constituents
    c) Automation & Robotic Platforms
A

QIAcube connect or classic QIAcube

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44
Q

DNA Advisory Board (DAB) requires this standard of Human-Specific DNA quantitation

A

Standard 9.4 of Human-Specific DNA quantitation so the appropriate levels of human DNA can be included in the subsequent PCR amplification.

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45
Q

Multiplex STR typing works best with a

A

fairly narrow range of human DNA - typically .5 to 2.0 ng of input DNA works best with commercial STR kits.

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46
Q

DNA Quantification

A

determines the amount of HUMAN DNA in a sample

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47
Q

Polymerase Chain Reaction (PCR)

A

a laboratory technique for rapidly producing (amplifying) millions to billions of copies of a specific segment of DNA

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48
Q

A narrow concentration range is required to

A

“SEED” the PCR reaction of amplification

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49
Q

Too much or too little DNA gives rise to

A

artifacts - false positive or false negative alleles

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50
Q

DNA Quantification Test should measure

A

quality as well as quantity of DNA

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51
Q

Quantitating DNA is important for forensics because

A
  • If we can confidently determine the amount of DNA in an extract we can then ask:
    • Will mitochondrial sequence be required?
    • Should we use low copy number LCN methods of STRs?
    • Re-extract the sample?
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52
Q

If problems occur in the STR typing process we can have confidence that the

A

DNA template is not the source (CE, cycler, kit)

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53
Q

3 Common Quantitation Methods

A
  1. Slot Blot Assay
  2. Interchelating Dye
  3. Quantitative PCR
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54
Q

Slot Blot Method

A
  • Detects primate DNA
  • Genomic DNA is denatured & small volume is spotted onto a nitrocellulose
  • DNA immobilized on a nylon membrane
  • Hybridization w/labeled 40 - nucleotide probe
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55
Q

Denatured DNA

A

When DNA is made single stranded and the single stranded denatured DNA links to the nitrocellulose membrane

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56
Q

Interchetaling Dye Method

A
  • Fluorescent Dye used
  • Not specific to HUMAN DNA
  • Fluorescence measure by spectrofluorometer
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57
Q

Quantitative PCR (qPCR or “real time PCR”)

A
  • Method of choice in most crime labs
  • More sensitive
  • Large range of detection
  • Amount of PCR product amplified during exponential phase of PCR correlates w/the initial concentration
  • Real-time PCR most common method in forensic lab
  • analyzes the amplification of a target sequence at each cycle of PCR
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58
Q

DNA replication begins w/the

A

unwinding of the DNA strands of the double helix

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59
Q

In DNA replication each strand is now exposed to a collection of free nucleotides that will be used to

A

recreate the double helix, letter by letter using base pairing.

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60
Q

PCR is the outgrowth of knowledge gained from understanding of how

A

DNA strands naturally replicate within a cell.

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61
Q

For the forensic scientists, PCR offers a distinct advantage in that it can amplify

A

minute quantities of DNA many millions of times

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62
Q

PCR Phases

A

Exponential Phase
Linear Phase
Plateau (“end point”)

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63
Q

Amount of PCR product amplified during exponential phase of PCR correlates with the

A

initial concentration

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64
Q

PCR Results produce

A
  • the standard curve from the known standards
  • Quantities from unknown samples
  • Quantitation data used to know how much goes into the next step in the profiling process – STR amplification
    .5 to 2 ng is the ideal amount
  • typically aim to use 1 ng
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65
Q

Advantages to using Real Time qPCR

A
  • The availability of commercial qPCR kits
  • Higher throughput & reduced user intervention
  • amenable to automation
  • High sensitivity
  • Large dynamic range: ~30 pg to ~ 30 ng
  • More accurate measurements of small quantities of DNA
  • Assays are target specific & can be multiplexed
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66
Q

Real Time qPCR Challenges

A
  • Subject to inhibition
  • Quantitation precision suffers at low copy numbers
  • when working below 100 pg qPCR is still subject to variability & uncertainty
  • qPCR quantities specific target sequences, it does not quantify “DNA”
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67
Q

Autosomal Short Tandem Repeats (STR) method requires

A

(Multiplex) <1ng of DNA to type of 20 STR loci

68
Q

Polymerase Chain Reaction (PCR) method

A
  • Molecular Xeroxing
  • An enzymatic process by which a specific region of DNA is replicated during repetitive cycles and GOAL is to generate MANY COPIEs for analysis
  • 3 Temperature phases replicate or “amplify” the desired DNA fragment(s)
69
Q

Copies of DNA generated in the PCR process are called

A

products or amplicons

70
Q

Steps in the PCR/Thermal Cycling

A
  1. The DNA is HEATED to separate it (denaturation)
  2. PRIMERs are added, which hybridize w/strands (annealing).
  3. DNA polymerase & free nucleotides are added to rebuild each of the separated strands (extension).
  4. Now, this cycle is repeated 25 to 30 times
71
Q

Primers

A

short strands of DNA used to target specific regions of DNA for replication

72
Q

Each strand of DNA is used a TEMPLATE to create a REPLICATE that permits DOUBLING of the number of target molecule w/

A

Each cycle of HEATING & COOLING

73
Q

Heating & Cooling samples in a precise thermal cycling pattern

A

over ~30 cycles & during each cycle, a copy of the target DNA sequence is generated for every molecule containing the target sequence

74
Q

Steps in the PCR/ Thermal Cycling

Using Multiplex PCR

A
  • Specific regions of the human genome are simultaneously targeted w/SEQUENCE-SPECIFIC oligonucleotide PCR primers
    *Copied w/DNA polymerase & doxynucleotide triphophate building blocks.
75
Q

In a matter of a few hours how many copies of the genome of each SPECIFIC REGION

A

Close to a billion

76
Q

The PCR amplification process incorporates

A

Fluorescently-labeled primers into the PCR products that enable multi-color fluorescence detection.

77
Q

PCR Amplification is based on

A

quantification results; 1ng of DNA is taken to be amplified

78
Q

Advantages of PCR amplification w/FORENSIC specimens

A
  • very small amounts of template required
  • Effective w/degraded DNA
  • Specific DNA sequences can be amplified simultaneously - multiplexing
  • HUMAN specific primers used - NO contaminant DNA
79
Q

Advantages of STR Kits

A
  • Quality control of materials is in the hands of the manufacture
  • Improves consistency in results across laboratories – SAME ALLELIC ladders used
  • Common LOCI & PCR conditions used
  • Simpler for the user obtain results
80
Q

Disadvantages of STR Kits

A
  • Contents may NOT be completely known to user
  • Higher cost to obtain results
81
Q

13 STR loci (plus Amelogenin) were initially chosen for analysis as they provided

A

a high level of individualization; also for ALL forensic laboratories contribute profiles of the same genetic markers to the DNA database.

82
Q

January 1, 2017, 20 Core CODIS STR Loci are required because

A
  1. facilitates greater discrimination
  2. assists in missing person investigations
  3. encourages international data sharing efforts by having more LOCI in common w/other countries for comparison
83
Q

Inhibitors of STR kits

A
  • interact w/DNA template (polymerase) causing amplification to FAIL- can be detected using an internal positive controll
  • MUST be REMOVED during extraction
84
Q

Inhibitors can be detected

A

using an internal positive control

85
Q

Common inhibitors in forensic samples

A
  • Heme from blood
  • Indigo dye from fabric
  • Melanin in hair samples
86
Q

Contamination of STR kits

A

PCR is very sensitive
* Pre & post PCR sample should be processed in separate areas or at DIFFERENT time
* Reagents for pre & post PCR should be separated
* Protective gear such as gloves, lab coats, facial masks, & hair caps
* Aerosol-resistant pipet tips
* DNA - free solutions & test tubes
* Controls must be used to detect contamination
* DNA profiles of lab members should be available for comparison - Staff ELIMINATION database

87
Q

Electrophoresis

A
  • technique that separates DNA amplification products based on SIZE and ELECTRICAL CHARGE
  • Phosphate groups on the background of the DNA molecule, readily give up their H+ IONS, leaving DNA molecules negatively charged
88
Q

Fluorescent Detection

A
  • amplification products have a fluorescent “label” attached to the primer
  • Label is seen through excitation via a laser & corresponding emission captured w/a camera
89
Q

Capillary Electrophoresis
Multiplex PCR produces 20 or more different sized DNA fragments representing …

A

different ALLELES that must be RESOLVED from each other.

90
Q

Capillary Electrophoresis
*Single based resolution is required to distinguished between…

A

closely spaced alleles (e.g., THO1 alleles 9.3 & 10)

91
Q

Capillary Electrophoresis (CE)
*a SEPARATION step is required to pull…

A

DIFFERENT sized fragments apart.

92
Q

Under electrical field, DNA will migrate…

A

AWAY from negative electrode (cathode), & move TOWARD the positive (anode).

93
Q

ABI (Applied Biosystems 3100 Genetic Analyzer is the

A

Most commonly used CE systems

94
Q

CE instruments electrokinetically inject the negatively charged DNA molecules from a

A

formamide-diluted sample of the PCR products mixed w/an internal size standard

95
Q

CE - The size standard is labeled w/a separate fluorescent dye to enable calibration of each analysis so that comparisons can be made between…

A

samples run at different times on the same instrument.

96
Q

CE - A polymer solution (sieve) inside the capillary permits resolution of DNA fragments differing by as little as a

A

a single base pair (bp) over a size range of approximately 100 to 400 bp

97
Q

CE - Formamide

A

denaturant solution that disrupts the hydrogen bonds between the complementary strands of the PCR products
*helps keep the strands denatured

98
Q

CE - Polymer

A

linear flexible chains act as obstacles to be navigated by the larger negatively charged DNA fragments
* Larger molecules are slowed down more than the smaller more agile DNA fragments, thus separating them

99
Q

CE - Fluorescent dyes are present on one strand of each PCR product due to incorporation of a

A

PCR primer during multiplex PCR amplification.
* These dyes are excited by laser as they pass a detection point in the CE instrument

100
Q

CE - 4, 5, or 6 fluorescent dyes used in STR analysis have

A

different chemical properties
* they emit light at slightly different chemical properties, they emit light at slightly different wavelengths enabling detection in different color channels.

101
Q

Requirements for ACCURATE STR Typing

A
  1. High precision
  2. Color separation of different dye sets used
  3. Resolution of at least 2 bp > 300 bp
  4. Reliable sizing over 75-450 bp region
102
Q

Advantages of CE

A
  1. The injection, separation, & detection steps can be fully automated
  2. Multiple samples can be run unattended by CE
  3. Tiny quantities of sample are consumed w/an injection
  4. Samples can easily be retested if needed w/o more preparation
103
Q

Disadvantage of CE

A
  1. Single capillary instruments CANNOT process high numbers of samples compared the gels.
  2. A high start-up cost
  3. Maintenance & supplies for the instruments can be expensive
104
Q

Allelic Ladder

A

is an artificial mixture of the ALL common alleles present in the human population for a particular STR marker
*the analysis software use these known peaks to determine the genotype of the unknown samples.

105
Q

Allele Calls

A

Comparison of the unknown fragments to the migration pattern of the allelic ladder allows determination of the genotype.
*software programs use macros to automatically make the comparison

106
Q

Discrimination power through Multiplexing

A

The loci used in STR systems have been shown to be inherited independently, which provides powerful statistical weight to genotypes.

107
Q

Thresholds

A

are set to separate signal from noise - are we are confident the peak is real?

108
Q

Signal peak height

A

is measured in relative fluorescence units (RFUs) that are related to the amount of DNA present in the sample loaded onto the analysis instrument

109
Q

Detection Threshold for Measuring DNA data

A
  • These thresholds for reliable data are determined through Validation Studies
  • typically vary from 50 RFU to 200 RFU
110
Q

Detection (analytical) Threshold

A
  • Dependent on instrument sensitivity
    *Impacted by instrument baseline noise
111
Q

Dropout (stochastic) Threshold

A
  • occurs when an allele is not copied during the PCR amplification process.
    *Dependent on biological sensitivity
  • Important in mixture interpretation
112
Q

DNA Data Analysis

A
  • The analyst carefully reviews the DNA data & checks software genotype calls & edits out artifacts
  • Software designates sample genotypes via comparison to the allelic ladder
113
Q

Determining the Genotypes of STR Fragments

A
  • Genotype for an STR locus is the number of repeat units of the allele
  • Genotype is determined by using the allelic ladder
114
Q

STR Results

A
  • Individuals will differ from one another in terms of their STR profile
  • STR genotype can then be put into a alpha numeric form for search on a DNA database
115
Q

Off-ladder allele

A

a rare allele that fails to match alleles in the ladder

116
Q

3 Types of “Off-Ladder” Alleles

A
  1. Below Ladder
  2. Above Ladder
  3. “Variant” between Ladder Alleles
117
Q

of Steps Involved in STR Genotyping

A
  1. Data Collection
  2. Color Separators
  3. Peak Identification
  4. Peak Sizing
  5. Comparison to Allelic Ladder
  6. Genotype Assignment to Alleles
  7. Data Review by Scientist
  8. Confirmation by second Scientist
118
Q

Biological Artifacts

A

a) Stuttering/Stutter
b) Non-Template Addition
c) Heterozygote Imbalance
d) Allelic Dropout

119
Q

Electrophoretic Artifacts

A

a) Pull up Peaks
b) Spikes

120
Q

Stuttering - Amplification Artifacts

A
  • Peaks that show up primarily 1 repeat less than the rule allele as a result of strand SLIPPAGE during DNA synthesis (PCR amplification)
  • Stutter peaks make mixture analysis MORE DIFFICULT
121
Q

Short repeat unit loci are

A

MORE likely to stutter

121
Q

Loci w/complex repeat sequences

A

have LESS stutter

122
Q

Proposed mechanisms for stutter products

A
  • During the DNA synthesis step of PCR amplification, a DNA polymerase slips
  • a region of the primer-template complex becomes unpaired, causing the template strand to form a loop
  • The result of the loop is a SHORTENED PCR product smaller than the template by a single repeat unit.
123
Q

Non-Template Adenylation

A

*Taq polymerase will often add an extra nucleotide to the end of a PCR product – usually and “A” (adenylation)
* DNA adds adenosine
*Multiplex STR kits use conditions that favor adenylation

124
Q

Heterozygote

A

Two alleles are different

125
Q

Heterozygote imbalance

A
  • 1 heterozygote allele has a larger peak than the other allele
    as a result of preferential amplification or mutations leading amplification fail
126
Q

Pull-up Peaks

A
  • Minor peak of 1 color on an electrophergram is pulled up from a major allelic peak in another color, when colors have overlapping spectra & can happen when a sample is OVERLOADED
127
Q

Spikes

A
  • Sharp peaks w/similar signal intensities that are present in all color panels of an electropherogram that is caused by air bubbles or urea crystals in the capillary, or voltage spikes
128
Q

SOFTGENETICS

A
  • STR Analysis Software
  • Compatible w/all commercial STR typing kits
  • GeneMaker HID superior to GeneMapper
    *Used in 28 countries
129
Q

STR Interpretation Software
Contamination Check

A
  • Allows data to be reviewed for possible contamination
  • Profile to profile comparison w/in a project
  • Comparison to lab’s elimination database
130
Q

STR Interpretation Software
Mixture Assessment

A
  • Attempts to determine an individual contributor to a mixture based on user’s pre-defined criteria
  • The software will calculate the probability of each genotypic combination based on the STR results
131
Q

In Mixture Assessment the resulting probabilities yield a possible contributor to the mixture along w/combined probability of

A

inclusion/exclusion (PI/PE), random man not excluded (RMNE), & a likelihood ratio (LR) when identifying a known contributor.

132
Q

Degraded DNA

A
  • Environmental exposure of biological evidence
  • UV light, humidity, high temps, bacterial contamination
  • Older methods of DNA Typing made it impossible to analyze
  • PCR amplification allows for detecting miniscule amounts of DNA
133
Q

Degradation can reduce the height of some peaks or

A

make them disappear entirely

134
Q
A
135
Q

Allelic dropout

A

partial DNA profile

136
Q

DNA Repair

A
  • PreCR Repair Mix
  • Recover damaged, compromised, or degraded DNA samples
  • Repair DNA prior to its use in DNA-related technologies
  • Easy-to-use
  • Does not harm DNA template
137
Q

Mixtures

A

Samples of DNA w/2 or more contributors
* Often encountered in forensic cases in which evidence recovered from the victim is mixed w/a suspect’s bodily fluids

138
Q

3 main factors determine the complexity of a mixture

A
  1. How many people contributed DNA to the mixture?
  2. How much DND did each person contribute?
  3. How degraded is the DNA?
139
Q

Drop-Outs

A

Degraded, or inhibited DNA & results i n partial DNA profiles, where the DNA from 1 or more contributors is NOT present at all loci.

140
Q

Drop-Ins

A

is the presence of low amounts of DNA w/in a profile that are not inherent to the DNA extract.

141
Q

Random Match Probability (RMP)

A

estimates the probability of a matching DNA profile (not the person of interest’s) w/in chosen population.

142
Q

Likelihood Ratio (LR)

A

is NOT a probability but rather a RATIO of 2 probabilities that evaluates the evidence given 2 or more mutually exclusive propositions:

LR = Pr(EIH1)/Pr(EIH2)

*E is the evidence - DNA profiles
H1 is the proposition that the POI is the contributor of DNA
H2 is the proposition the some other randomly selected individual from the population unrelated to the POI

143
Q

Combined Probability of Inclusion (CPI) or Random Man Not Excluded (RMNE)

A
  • Is the simplest method
  • Not an interpretation method
  • It is used to ESTIMATE the proportion of unrelated individuals in the population that could be included as possible contributors to the profile
  • Can be OVERLY INCLUSIVE - dealing w/low-level mixture data
144
Q

Steps in analyzing Mixtures

A
  1. Determine the genotypes of ALL alleles & identify the number of contributors
  2. Estimate rations of the contributors
  3. Compare reference samples
145
Q

Steps in Mixture INTERPRETATION

A
  1. Identify the Presence of a Mixture
  2. Designate Allele Peaks
  3. Identify the number of Potential Contributors
  4. Estimate the Relative Ratio of the Individuals Contributing to the Mixture
  5. Consider ALL Possible Genotype Combinations
  6. Compare Reference Samples
146
Q

The Key in Mixtures is to ask the right questions:

A
  1. How complex is the mixture in terms of number of contributors & the amount of DNA from each?
  2. How confident can we be that the DNA is relevant to the case?
  3. What other types of evidence exist to corroborate the DNA evidence?
147
Q

Interpretation of STR Profiling Results

A
  • Inclusion - Match
  • Exclusion
  • Inconclusive Result
148
Q

CORE STR Markers -
Loci should NOT be linked or inherited together

A
  • Forensic STR loci are usually on different chromosomes to be sure they are not linked
    ** Loci that are far apart on the same chromosome may be used
  • Have few amplification artifacts such as stutter
149
Q

FBI & NIST raising standard of STR loci from 13 to 20

A
  • Quality Assurance Standards
  • Makes international DNA searches more effective
  • Better for degraded samples
  • If 7 markers are dropped out, you still have what is considered a full profile in 2-16
150
Q

With the NEW 20 CORE STR Markers the chances that 2 people who are not closely related have the same number of repeats at both copies of all 20 markers is

A

LESS than 1 in a billion billion

151
Q

Database

A

is an organized file or files of data that can be searched to retrieve information

152
Q

DNA Databases

A

compare profiles derived from evidentiary samples to a database of DNA profiles obtained from known individuals to provide law enforcement w/investigative leads

153
Q

CODIS

A

enables federal, state, and local crime labs to exchange & compare DNA profiles electronically.
* Consists of NDIS, SDIS, & LDIS

154
Q

Categories of forensic/offender DNA records may be stored & searched in NDIS:

A

Accordance w/the Federal DNA Act
* Arrestee
* Convicted Offender
* Detainee
* Forensic Mixture
* Forensic Partial
* Forensic Unknown
* Juvenile
* Legal
* Multi-allelic Offender

155
Q

3 Criteria for determining the eligibility of a DNA record

A
  1. That a crime has been committed
  2. That demonstrates the DNA sample was recovered directly from the crime scene & is attributed to the putative
  3. The elimination sample(s) have been requested, if applicable
156
Q

Missing Person Index

A
  • Unidentified Human Remains
  • Missing persons direct reference samples
  • Family reference samples
157
Q

Only the following information is stored & can be searched at the national level:

A
  1. The DNA profile
  2. The Agency Identifier of the agency submitting the DNA profile
  3. The Specimen Identification Number
  4. The DNA laboratory personnel associated w/a DNA profile analysis
158
Q
A
158
Q

Requirements for the DNA data submitted to the NDIS:

A
  1. DNA data must be in accordance w/FBI director’s Quality Assurance Standards
  2. DNA data must be generated by an accredited lab
  3. Accredited lab undergoes External Audit every 2 years
  4. Must be 1 of the Categories of data acceptable at NDIS
  5. Must meet minimum CODIS core Loci requirements
  6. PCR data must be generated using PCR accepted kits
  7. Laboratories must have & follow expungement procedures
159
Q

Searching CODIS -
High Stringency

A

is a search that requires all alleles to match between the 2 DNA profiles

160
Q

Forensic Partial & Forensic Mixture Indices

A

Where DNA profiles that are partial of mixtures are maintained

161
Q

CODIS Searching -
Moderate Stringency

A

a search that requires all alleles to match, but the 2 DNA profiles can contain a different number or alleles

162
Q

Partial Matches as defined by FBI

A

between 2 single source profiles have at each locus all of the alleles of 1 sample represented in the other sample

** NOT an EXACT MATCH of 2 profiles

163
Q

Sex & Red Blood cells are the only cells that do not have

A

a complete copy of your DNA

164
Q
A

Forensic Biological Evidence (3 decks)

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