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Forensics > Unit 4: DNA > Flashcards

Unit 4: DNA Flashcards

1
Q

What does DNA stand for?

A

Deoxyribonucleic Acid

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2
Q

Does anyone have the exact same DNA?

A

No two people have the exact same DNA unless they are identical twins

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3
Q

What is DNA fingerprinting also known as?

A

DNA profiling, in which it is a technique that helps scientists distinguish between individuals of the same species using only samples of their DNA

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4
Q

The process of DNA fingerprinting was invented by?

A

Alec Jeffreys at the University of Leicester in 1985

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5
Q

What can DNA fingerprinting be used for?

A
  1. Identify the bodies of victims
  2. Paternity
  3. Identify victims of war and large-scale disasters
  4. Track genetically modified crops
  5. Settle immigration disputes
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6
Q

Small amount of biological evidence left at crime scenes is called…

A

Trace evidence

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7
Q

What are some examples of biological evidence?

A

Saliva, blood, skin

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8
Q

What type of evidence is DNA evidence?

A

Because it identifies a specific person, it is considered individual evidence

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9
Q

What does it mean when the DNA fingerprint comes up as no match?

A

It is a very powerful argument for excluding an individual

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10
Q

Ambiguous or no result

A

This means that there is no result because there were problems with the specimen or the test

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11
Q

Match

A

The crime scenes DNA and the suspect DNA are the same but it is the function of the lab, expert witnesses, and the courts to determine guilt

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12
Q

What type of acid is DNA?

A

Nucleic Acid and it is found in the nucleus of your cells

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13
Q

How many pairs of chromosomes do human cells have?

A

23 pairs

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14
Q

How many total chromosomes do humans have?

A

46

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15
Q

How many chromosomes are in sperm and egg cells

A

23 because they are not in pairs

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16
Q

What are genes?

A

Each chromosome pair can be broken into smaller segments; genes control the traits of the organism, and therefore can vary between individuals

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17
Q

DNA has how many nitrogenous bases…

A

4

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18
Q

What are the 4 nitrogenous bases?

A
  1. Adenine (A)
  2. Thymine (T)
  3. Guanine (G)
  4. Cytosine (C)
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19
Q

These bases form according to the base pairing rule which is…

A
  1. Adenine binds with only THYMINE
  2. Cytosine binds with GUANINE

These pairs are considered to be complementary
i. if one strand of DNA has the genetic code: ATCTGC
TAGACG - its complementary strand would read

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20
Q

What shape is DNA strand?

A

DNA is made when two strands twist together in a shape called the double helix

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21
Q

What are the sides of the helix called?

A

It is referred to as the backbone of DNA which is made up of alternating sugar (the sugar is called deoxyribose) and phosphate molecules

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22
Q

What are the rungs of the helix made up of?

A

They are made up of the paired nitrogenous bases (A-T, C-G) which help to code the DNA with instructions for the cell

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23
Q

What is DNA in Chromosomes called?

A

Nuclear DNA

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24
Q

Is nuclear DNA from both the mother and father?

A

True and it is identical in all cells of an individuals body

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25
Q

Is mitochondrial DNA linear or in the form of a circular loop?

A

In a circular loop and it is only inherited from their mother

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26
Q

What is the human genome?

A

Is the total amount of DNA in a cell. It is contained in both the nucleus and mitochondria

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27
Q

How many base pairs does the human genome have?

A

3 billion base pairs

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28
Q

What is the purpose of the genome?

A

Is to code the blueprint for the human body and how it works, it is responsible for telling the body to make proteins and other needed molecules

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29
Q

What are exons?

A

Exons are encoded DNA with directions to build molecules

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30
Q

What are introns?

A

They are un-encoded DNA, that do not code for the production of molecules and are make up most of DNA and are known as junk DNA and they are important in gene splicing and have an important role in biology

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31
Q

Are most of the human genome the same in all individuals?

A

Yes it is the same, but some variation exists among individuals

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32
Q

Where is most of the variation in DNA found?

A

In the non-coding DNA or introns and much of the non-coding DNA is in the form of repeated base sequences and some of these sequences can be repeated many times

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33
Q

What type of charge does DNA have?

A

Slightly negative

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34
Q

What are Polymorphisms?

A

They are non-coded DNA segments that have unique patterns of repeated base sequences that are unique to individuals

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35
Q

What are Variable Numbers of Tandem Repeats?

A

VNTR are 9 to 80 bases in length

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36
Q

What are Short Tandem Repeats?

A

STRs are 2 to 5 bases in length

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37
Q

What are SNP’s?

A

Single Nucleotide Polymorphisms like T, A

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38
Q

VNTR and STR data from DNA fingerprints can be analyzed for two main purposes….

A

i. tissue matching (comparing DNA evidence from a crime scene with DNA from a suspect, and how it looks two samples that have the same band pattern are from the same person)

ii. inheritance matching (comparing family member’s DNA for proof of familial relationships and how it looks each band in a child fingerprint must be present in at least one parent 50% from mom and 50% from dad)

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39
Q

What is Trace Evidence?

A
  • Is the small amount of evidence left at a crime scene is very small and therefore considered to be trace evidence
  • A problem with analyzing trace evidence is that forensic tests will destroy the evidence sample, as in the case with DNA
  • Therefore, prior to DNA fingerprinting, PCR us used
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40
Q

What is used to prevent DNA evidence from being destroyed and to replicate DNA samples?

A

PCR which is Polymerase Chain Reaction; PCR is a technique that makes thousand of copies of segments of DNA that investigators want to analyze

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41
Q

How does PCR work?

A

Crime scene (template) DNA is mixed with nucleotides, an enzyme known as DNA polymerase, and primase

Primers are short segments of complementary DNA that base-pair with the template DNA upstream of the region of interest and serve as recruitment sites for the polymerase

Cycles of denaturation, annealing, and extension are repeated to achieve exponential amplification of the target sequence, allowing for billions of DNA copies to be produced in just a few hours

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42
Q

To avoid DNA evidence contamination, crime scene investigators should…

A
  1. Wear disposable gloves and change them often
  2. Use disposable instruments for handling each sample
  3. Avoid talking, coughing, or sneezing over evidence
  4. Do not touch your face or body when collecting or packaging evidence
  5. Air-dry evidence before packaging. If evidence cannot be dried, it may be frozen
  6. Avoid using plastic bags to store evidence that contains DNA; use paper bags or envelopes
  7. Keep evidence cool and dry during transportation and storage. Avoid direct sunlight which can damage DNA
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43
Q

Steps of DNA Fingerprinting

A

Step 1: Extraction of the DNA
Step 2: Cut the DNA into restriction fragments RFLP’s, Restriction Fragment Length Polymorphisms
Step 3: Amplification (making many copies of those fragments) use PCR
Step 4: Electrophoresis (a process that separates RFLPs, according to their length, creating a DNA fingerprint)

44
Q

How does Gel Electrophoresis Work?

A
  1. Restriction enzymes cleave DNA into smaller segments of various sizes
  2. DNA segments are loaded into wells in a porous gel. The gel floats in a buffer solution within a chamber between two electrodes
  3. When an electric current is passed through the chamber, DNA fragments move toward the positively-charged cathode
  4. Smaller DNA segments move faster and farther than larger DNA segments
45
Q

Analysis of DNA Fingerprints

A

DNA fingerprints should look like a striped column. In order for DNA fingerprints to match, the columns must have bands in the exact same places with the exact same widths

46
Q

What does DNA Fingerprinting help with?

A
  1. Match a crime scene DNA with a suspect
  2. Eliminate a suspect
  3. Free a falsely imprisoned individual
  4. Determine maternity, paternity, or match to another relative
  5. Identify human remains
47
Q

What is the point of DNA?

A

DNA contains genetic codes that determine proteins that make up our physical features

48
Q

What are Purines?

A

They are double ring structures (adenine and guanine are purines)

49
Q

What are Pyrimidines?

A

They are single ring structures (thymine and cytosine are pyrimidines)

50
Q

Do purines always bond with pyrimidines?

A

YES

51
Q

What is Chargaff’s Rule?

A

It states that DNA from any cell should have a 1:1 ratio of pyrimidine and purine bases (as per the base pairing rules)

  • In other words, the amount of guanine is equal to cytosine; and the amount of adenine is equal to thymine

ex: if a DNA molecule contains 28% cytosine, we can figure out how much guanine, thymine, and adenine are present in the molecule

Cytosine (28%)
Guanine (28%)
Adenine (22%)
Thymine (22%)

52
Q

Who are Watson and Crick?

A

They determined the shape of DNA based on X-ray diffraction their work was more of a puzzle completion, they figured out that the shape of DNA was a double helix (2 strands of nucleotides and helix is twisted)

53
Q

Who was Rosalind Franklin?

A

She put work and information in to determine the structure of DNA

54
Q

What is Photo 51?

A

It was Rosalind Franklin’s work that confirmed the helical structure of DNA

55
Q

How do the bases bond together?

A

Using hydrogen bonds

56
Q

How many hydrogen bonds do adenine and thymine have?

A

2 bonds

57
Q

How many hydrogen bonds do guanine and cystosine have?

A

3 bonds

58
Q

Are hydrogen bonds the weakest type of bond?

A

True

59
Q

When does DNA replication occur?

A

During the synthesis phase of the cell cycle which is before the cell divides

60
Q

DNA Replication the First Step…

A

The first step is to break those hydrogen bonds between the bases an enzyme called DNA helicase breaks the hydrogen bonds and unzips the original parent DNA molecule

61
Q

What does the enzyme DNA Helicase do?

A

It breaks the hydrogen bonds and unzips the original parent DNA molecule

62
Q

DNA Replication Step 2…

A

Once the DNA strands are unzipped, the nucleotides are exposed

The second step involves another enzyme called DNA Polymerase this enzyme reads the DNA and determines which NEW nucleotides to add to the parent strand

63
Q

What is DNA Polymerase?

A

This enzyme reads the DNA and determines which new nucleotides to add to the parent strand

64
Q

What are Replication Forks?

A

They form at multiple points in the DNA to speed up replication

65
Q

What do two replication forks make?

A

Replication bubbles

66
Q

What do 5’ and 3’ mean?

A

Since DNA is a 3-dimensional molecule made of linked nucleotides, it really doesn’t have a “left” or “right”; “up” or “down”. If we have ti refer to DNA’s direction we use 5’ and 3’ (5 prime and 3 prime). Recall that deoxyribose is a 5 carbon sugar. These numbers (5,3) are in respect to the position of the 5-carbon sugar

67
Q

What does it mean when DNA is Antiparallel?

A

DNA molecules are antiparallel- meaning the two strands run parallel to one another but in different directions (it always looks like one strand is up-side-down relative to the other)

And during DNA replication, DNA polymerase reads the parent molecule in the 3’ and 5’ direction (opposite)

How to remember… when you read a book you would read chapters 3-5

68
Q

What is the Leading Strand?

A

One new strand will move continuously TOWARD the replication fork

69
Q

What is the Lagging Strand?

A

Because the strands are anti-parallel, the other strand will move AWAY from the replication fork

70
Q

What are Okazaki fragments?

A

They are short segments of new DNA on the lagging strand

71
Q

How many strands are on the final product of DNA Replication?

A

Two molecules of DNA (4 strands total since each molecule is double stranded)

72
Q

Is DNA semi-conservative?

A

True meaning each time DNA is copied, the original DNA molecule is saved, each new molecule consists of one parental strand, and one (new) daughter strand

73
Q

Why is DNA important?

A

DNA is important because it has the recipe for making proteins

74
Q

What is RNA?

A

Ribonucleic Acid is the copy of DNA code; think of DNA as library it contains very important books, but no checking them out! However, copies can be made and those can leave the library, the copies are like the RNA. It is a nucleic acid and is made of linked nucleotides (like DNA)

75
Q

What are the differences between DNA and RNA?

A
  1. DNA is double-stranded and RNA is single-stranded, this means that RNA is smaller than DNA
  2. RNA contains 4 nitrogen bases adenine, guanine, cytosine, and uracil thymine is not present in RNA
  3. RNA contains the 5-carbon sugar ribose which has more more oxygen atom than deoxyribose whereas DNA has deoxyribose
76
Q

What is Messenger RNA?

A

Messenger RNA (mRNA) is complementary to the original strand of DNA. mRNA is first created in the nucleus and then travels to the ribosomes in the cytoplasm. mRNA uses the DNA’s code (or message) to make proteins

77
Q

What are Proteins made up of?

A

Amino acids

78
Q

What are codons?

A

Individual DNA codes the codons correspond to specific amino acids

79
Q

What do codons consist of?

A

They consist of groups of 3 nucleotides called triplets, and each codon codes for one amino acid this is where we need RNA’s help

80
Q

mRNA is always complementary to the template DNA strand

A

True

81
Q

What are the mRNA codons?

A
  1. UGC (cysteine)
  2. AAU (asparagine)
  3. CGG (arginine)
82
Q

How many amino acids are there?

A

Though there are only 20 different amino acids, they are sequenced differently and come in different shapes to make for thousands of different proteins

83
Q

The process of protein synthesis

A

It is a 2 part process in which DNA is decoded into corresponding proteins

  1. The first process is known as transcription (mRNA is created by transcribing the DNA’s code)
  2. The second process is translation (the mRNA that was manufactured during transcription is translated into an amino acid sequence (proteins)
    - Occurs in the nucleus and cytoplasm
84
Q

What are the three types of RNA?

A
  • mRNA
  • tRNA (transfer RNA helps transfer amino acids to the corresponding mRNA codons, tRNA is always complementary to the mRNA strand, they are also referred to as “anti-codons” because they are complimentary to mRNA codons)
  • rRNA (a major component of ribosomes; also helps bond amino acids together to make polypeptides (proteins)
85
Q

What are proteins made of?

A

amino acids

86
Q

What are some start codons?

A

AUG codes for the amino acid methionine

87
Q

What are some stop codons?

A

UAA, UAG, UGA

88
Q

Where is DNA located in the cell?

A

Nucleus

89
Q

DNA is made up of individual units called…

A

Nucleotides

90
Q

Purines only bond with pyrimidines and vice versa

A

True

91
Q

DNA’s shape is described as a…

A

double helix

92
Q

What does DNA do?

A

DNA contains genetic codes that determine proteins that make up our physical features

93
Q

What is the relationship between DNA and amino acids?

A

Amino acids are the building block of proteins. A gene’s DNA sequence determines the order of amino acids that make up a protein, so if there are changes in the DNA sequences there would be a change in the amino acid sequence as well

94
Q

What is DNA coiled into?

A

Chromosomes

95
Q

Proteins called _____ and _____ help to keep the DNA ____

A

Nucleosomes and histones; coiled

96
Q

What is genetic genealogy?

A

It is the combination of genetic analysis with traditional historical and genealogical research to study family history

97
Q

What is genealogy used for?

A

For forensic investigations, it can be used to identify remain by tying the DNA to the family of a missing person

Or to point to the likely identity of a perpetrator

  • By comparing a DNA sample to a database of DNA from volunteer participants, it is possible to determine whether there are relatives of the DNA sample in the database and how closely related they are
  • This information can then be cross-referenced with other data sources used in traditional genealogical research, such as census records, vital records, obituaries and newspaper activities
98
Q

What does genetic genealogy use to identify DNA?

A

It uses autosomal DNA single nucleotide polymorphisms (SNP’s) to determine how closely related 2 individuals are

Unlike other genetic markers such as mitochondrial DNA or Y chromosome DNA, they must make sure that DNA is inherited from all ancestral lines and passed on by both males and females and thus can be used to compare 2 individuals regardless of how they are related

99
Q

Who was Joseph James DeAngelo aka the Golden State Killer

A
  • He was an American serial killer, serial rapist, burglar and former police officer who committed at least 13 murders, 51 rapes, and 120 burglaries across California between 1974 and 1986
100
Q

What were his nicknames?

A

-burglary: Visalia ransacker
- sexual assaults: east area rapist
- murders: the original nightstalker
- the golden state killer

101
Q

Who was Michelle McNamara?

A

To heighten the awareness of the case, the writer coined the name golden state killer in early 2013

102
Q

What happened in James’ early life that could have led to his behaviour?

A
  • Saw his younger sister raped
  • Was abused by his father
  • He committed burglaries and animal torture as a teen
103
Q

How did Deangelo get caught?

A
  • They uploaded the killers DNA profile from a rape kit to the genealogy website GEDmatch
  • The website identified 10-20 people who had the same great great great grandparents as the Golden State Killer; and they used this list to create a family tree from this tree they got 2 suspects one ruled out by a DNA test leaving DeAngelo the main suspect
  • DNA was collected from the door handle of his car and both samples match the Golden State crimes
104
Q

What is DNA Phenotyping?

A

It is the prediction of physical appearance from DNA (think photograph what do you see physical features)

  • It can be used to generate leads in cases where there are no suspects or database hits, to narrow suspect lists, and to help solve human remains cases
  • DNA carries the genetic instructions for an individual’s characteristics, producing a wide range of appearances among people
  • Snapshot reads tens of thousands of genetic variants (genotypes) from a DNA sample and uses this info to predict what an unknown person looks like
  • It predicts genetic ancestry, eye colour, hair colour, etc
105
Q

Can you figure out age, BMI and facial hair with genetic phenotyping?

A

False

106
Q

What is touch DNA/trace DNA?

A
  • It is a forensic method for analyzing DNA left at the scene of a crime
  • It is called “touch DNA” because it only requires very small samples, for example from the skin cells left on an object after it has been touched or handled, or from footprints
  • Touch DNA analysis only requires seven or eight cells from a layer of skin
  • This technique has been criticized for high rates of false positives due to contamination
107
Q

When is Touch DNA or Trace DNA used mostly?

A

To eliminate suspects rather than prosecution because of the high chance of contamination

Forensics (6 decks)

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