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Forensic Science > 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
Q

Recessive

A

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

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26
Q

Each chromosome is DNA, or a…

A

single polymeric molecule

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27
Q

Nucleic acids

A

Organic substance whose molecules consist of many nucleotides linked in a long chain; has a conserved general structure

28
Q

Nucleic acid structure (3)

A

Phosphate group
5 carbon sugar (either ribose or deoxyribose)
Nitrogenous base

29
Q

DNA Structure (3)

A

4 nucleotides
Sugar-phosphate repeating to make the backbone
Bases encoding the information stuck out from the backbone

30
Q

Polymer

A

Substance that has a molecular structure consisting mostly of a large number of similar units bonded together (DNA)

31
Q

DNA Nitrogenous Bases (4)

A

Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)

32
Q

DNA Double Helix (2)

A

Strand in an anti-parallel format

Moves from 5’ to 3’

33
Q

Purines

A

Adenine and Guanine - bigger

34
Q

Pyrimidines

A

Cytosine and Thymine

35
Q

Sequence variation

A

Genes encode different genotypes through genetic variation

36
Q

Where do the restriction enzymes cut?

A

At the site of molecular palindromes
ACT AGT
TGA TCA

37
Q

CODIS

A

Combined DNA Index System; used by the FBI to link crimes to known offenders

38
Q

How many bases are in a human genome?

A

3 billion

39
Q

DNA variations exist in

A

genes (coding regions)

the spaces between genes (non-coding regions)

40
Q

DNA profiling analyzes…

A

Short Tandem Repeats (STRs)

41
Q

Length Polymorphisms

A

Variation in length at a particular locus

42
Q

Sequence polymorphism

A

Variation in sequence of base pairs at a particular locus

43
Q

Approaches to to DNA Analysis (4)

A
  1. Restriction Fragment Length Polymorphism
  2. Variable Number Tandem Repeat
  3. Short Tandem Repeat
  4. Single Nucleotide Polymorphism
44
Q

VNTR

A

Variable Number Tandem Repeat; variation in sequence length; minisatellites

45
Q

STR

A

Short Tandem Repeat; Variation in sequence length; microsatellites

46
Q

SNP

A

Single Nucleotide Polymorphism; variation in DNA sequence

47
Q

Tandem Repeats

A

Pattern of two or more nucleotides is repeated

48
Q

RFLP Process

A
  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
Q

DNA Probe

A

Small fragment of nucleic acid that is labelled with an enzyme or fluorescent dye tag

50
Q

Current method of DNA fingerprinting

A

Autosomal Short Tandem Repeats (STR)

51
Q

Where is STR found?

A

Non coding regions of nuclear DNA

52
Q

Benefits of STR

A

Faster and cheaper
Doesn’t degrade the DNA
Requires less DNA
Greater power of discrimination

53
Q

STR Steps (5)

A
  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
Q

Polymerase Chain Reaction (PCR)

A

Molecular Xeroxing; three temperature phases carried out in a thermal cycler replicate, or “amplify,” the desired DNA fragments

55
Q

PCR Temperature Phases

A
  1. Template denaturation (high temp)
  2. Primer anneal (low temp)
  3. DNA synthesis (medium temp)
56
Q

PCR Process

A
  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
Q

Disadvantages of PCR (2)

A

DNA may not amplify due to PCR inhibitors

Contamination from other DNA sources can occur without proper technique and protocol

58
Q

STR PCR Analysis

A

PCR primers bracket the locus
DNA polymerase copies the section
Uses multiple loci

59
Q

Co-Mingled DNA

A

Fluids at a crime scene become mixed and contain more than one person’s DNA

60
Q

Co-Mingled DNA Solution

A

Must compare the co-mingled DNA with the victim’s and suspect’s DNA

61
Q

How to calculate the likelihood of the DNA sequence

A

Multiple frequency of each allele, then divide by one

There’s a one in x chance that another person has this DNA

62
Q

How many markers are on the CODIS system?

A

13

63
Q

Specialized PCR-based systems

A

mtDNA - requires less material, maternal
Y-STRs - STRs on the Y chromosome, paternal
SNPs - single nucleotide polymorphisms

64
Q

RFLP Strength

A

5 RFLP probes provide almost exclusive identity

65
Q

RFLP Weaknesses

A

Requires a lot of undegraded DNA
Process is destructive
Slow and costly
Multiple technical steps

Forensic Science (4 decks)

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