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HDSO Forensics > DNA Analysis > Flashcards

DNA Analysis Flashcards

1
Q

What was the first DNA fingerprinting method?

A

Restriction Fragment Length Polymorphism (RFLP)

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2
Q

Who created RFLP and how?

A

Alec Jeffreys was searching for disease DNA markers and attempted to use it as personal identification.

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3
Q

Uses of DNA evidence analysis (6)

A 
Criminal and civil cases
Find missing persons
Establish paternity
Medical diagnostics
Identifying the dead
Rape cases
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4
Q

DNA Evidence Sources (6)

A 
Blood (WBCs)
Semen
Saliva (cheek cells)
Hair (root follicle)
Teeth (root and nerve)
Feces
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5
Q

Where does DNA survive the longest in the body?

A

In the root and nerve of the teeth

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6
Q

Cell

A

The smallest unit of life

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7
Q

The two organelles in animal cells that contain DNA

A

The nucleus

Mitochondrion

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8
Q

Nucleus

A

The brain of the cell in the form of chromosomes inherited from parents

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9
Q

Mitochondrion DNA

A

mtDNA; Inherited from the mother; can get more DNA from a blood sample and it doesn’t change between generations

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10
Q

All cells contain DNA except…

A

Red blood cells

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11
Q

Functions of DNA (2)

A
  1. Transmits information from one generation of cells to the next
  2. Provides the information for the synthesis of proteins necessary for cellular function
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12
Q

Chromosomes

A

Where genetic information is organized

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13
Q

How many pairs of chromosomes are in most humans?

A

23 pairs

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14
Q

How many autosomal chromosomes?

A

22 pairs, the last pair are sex chromosomes (XX/XY)

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15
Q

Genes

A

The blueprint for a specific type of protein or RNA in the body; information blocks of characteristics or traits

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16
Q

Where are genes? How many?

A

Hundreds of thousands in each chromosome

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17
Q

Locus

A

A position that a gene is present at

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18
Q

Alleles

A

Different versions of the same gene

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19
Q

Genotype

A

Genetic composition of an organism, as opposed to its physical appearance (ie. the combination of alleles it possesses)

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20
Q

Phenotype

A

Characteristics, both externally visible and physiological, of an organism determined by its genes, modified by the environment

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21
Q

Diploid

A

Containing pairs of chromosomes (humans)

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22
Q

Homozygous

A

A gene pair of the two same alleles (AA)

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23
Q

Heterozygous

A

A gene pair of two different alleles (AO)

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24
Q

Dominant

A

Allele that is expressed in the phenotype of a heterozygous; if two forms are present, the allele that is actually expressed is dominant

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25
Recessive
Allele that is not expressed in the phenotype when two different alleles are present in the cells of an organism; only appears with double recessive
26
Each chromosome is DNA, or a...
single polymeric molecule
27
Nucleic acids
Organic substance whose molecules consist of many nucleotides linked in a long chain; has a conserved general structure
28
Nucleic acid structure (3)
Phosphate group 5 carbon sugar (either ribose or deoxyribose) Nitrogenous base
29
DNA Structure (3)
4 nucleotides Sugar-phosphate repeating to make the backbone Bases encoding the information stuck out from the backbone
30
Polymer
Substance that has a molecular structure consisting mostly of a large number of similar units bonded together (DNA)
31
DNA Nitrogenous Bases (4)
Adenine (A) Guanine (G) Cytosine (C) Thymine (T)
32
DNA Double Helix (2)
Strand in an anti-parallel format | Moves from 5' to 3'
33
Purines
Adenine and Guanine - bigger
34
Pyrimidines
Cytosine and Thymine
35
Sequence variation
Genes encode different genotypes through genetic variation
36
Where do the restriction enzymes cut?
At the site of molecular palindromes ACT AGT TGA TCA
37
CODIS
Combined DNA Index System; used by the FBI to link crimes to known offenders
38
How many bases are in a human genome?
3 billion
39
DNA variations exist in
genes (coding regions) | the spaces between genes (non-coding regions)
40
DNA profiling analyzes...
Short Tandem Repeats (STRs)
41
Length Polymorphisms
Variation in length at a particular locus
42
Sequence polymorphism
Variation in sequence of base pairs at a particular locus
43
Approaches to to DNA Analysis (4)
1. Restriction Fragment Length Polymorphism 2. Variable Number Tandem Repeat 3. Short Tandem Repeat 4. Single Nucleotide Polymorphism
44
VNTR
Variable Number Tandem Repeat; variation in sequence length; minisatellites
45
STR
Short Tandem Repeat; Variation in sequence length; microsatellites
46
SNP
Single Nucleotide Polymorphism; variation in DNA sequence
47
Tandem Repeats
Pattern of two or more nucleotides is repeated
48
RFLP Process
1. Purify DNA from the sample 2. Restriction enzymes cut DNA whenever they encounter a molecular palindrome 3. Gel electrophoresis 4. Southern Blot 5. Transfer to nylon membrane 6. Incubate with a radiolabeled DNA probe 7. Expose x-ray to membrane 8. Create different probes to mark different markers
49
DNA Probe
Small fragment of nucleic acid that is labelled with an enzyme or fluorescent dye tag
50
Current method of DNA fingerprinting
Autosomal Short Tandem Repeats (STR)
51
Where is STR found?
Non coding regions of nuclear DNA
52
Benefits of STR
Faster and cheaper Doesn't degrade the DNA Requires less DNA Greater power of discrimination
53
STR Steps (5)
1. DNA sample is collected 2. DNA is extracted 3. DNA is amplified in a thermal cycle 4. Amplified DNA is separated 5. Analysis
54
Polymerase Chain Reaction (PCR)
Molecular Xeroxing; three temperature phases carried out in a thermal cycler replicate, or "amplify," the desired DNA fragments
55
PCR Temperature Phases
1. Template denaturation (high temp) 2. Primer anneal (low temp) 3. DNA synthesis (medium temp)
56
PCR Process
1. DNA is split into single strands by high temp 2. Primers attach at a lower temp 3. Primers with polymerase extend by stepwise addition 4. DNA is amplified 5. After 25 cycles, there are 30 million copies
57
Disadvantages of PCR (2)
DNA may not amplify due to PCR inhibitors | Contamination from other DNA sources can occur without proper technique and protocol
58
STR PCR Analysis
PCR primers bracket the locus DNA polymerase copies the section Uses multiple loci
59
Co-Mingled DNA
Fluids at a crime scene become mixed and contain more than one person's DNA
60
Co-Mingled DNA Solution
Must compare the co-mingled DNA with the victim's and suspect's DNA
61
How to calculate the likelihood of the DNA sequence
Multiple frequency of each allele, then divide by one | There's a one in x chance that another person has this DNA
62
How many markers are on the CODIS system?
13
63
Specialized PCR-based systems
mtDNA - requires less material, maternal Y-STRs - STRs on the Y chromosome, paternal SNPs - single nucleotide polymorphisms
64
RFLP Strength
5 RFLP probes provide almost exclusive identity
65
RFLP Weaknesses
Requires a lot of undegraded DNA Process is destructive Slow and costly Multiple technical steps

HDSO Forensics (10 decks)

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