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CM5002 Forensic Science > DNA > Flashcards

DNA Flashcards

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1
Q

What does it mean when pairs of chromosomes are homologous?

A

They have the same size and contain the same genetic material

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2
Q

What is the relationship between genomes, chromosomes, genes and DNA?

A

The genome is divided into chromosomes. Chromosomes contain genes. Genes are made of coding region of DNA
Genomes > chromosomes > DNA > genes

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3
Q

What is a genome?

A

Entire set of hereditary instructions (genetic material) for building, running, maintaining and organism and passing life on

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4
Q

What are chromosomes?

A

Nuclear DNA packaged in specific structural units (in nucleated cells). Within each one, the DNA is wound around small proteins called histones

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5
Q

What are genes?

A

Coding region of DNA material in chromosomes. Number of genes vary from species to species. More complex organisms have more genes

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6
Q

What is the non-coding region of DNA?

A

junk DNA with no genetic information

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7
Q

What is DNA?

A

A polymer of nucleotides

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8
Q

What is a nucleotide?

A

A sugar, a phosphate and a base = a nucleotide

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9
Q

Why do we have 4 nucleotides?

A

Ribose + phosphoric acid = phosphate acid of deoxyribose. Replace a hydroxyl group in ^ with a base to get a nucleotide
Base: adenine/guanine/cytosine/thymine, hence there are 4 types of nucleotides

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10
Q

What is a double helix?

A

DNA consists of two chains wound together (double helix). Held in place by hydrogen bonding, where the bases in DNA will hydrogen bond to each other

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11
Q

What is complementary base pairing?

A

Favourable for A to pair with T, and G to pair with C

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12
Q

What is an amino acid?

A

A group of 3 nucleotides in a protein

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13
Q

What does DNA profiling use and why?

A

Junk DNA because it has great variability between different individuals

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14
Q

Describe the procedure of Restriction Fragment Length Polymorphism (RFLP). (7)

A
  1. Blood/semen sample about the size of a dollar coin
  2. DNA cut into fragments by a restriction enzyme
  3. DNA fragments are separated into bands by electrophoresis
  4. DNA band pattern on the electrophoretic gel is transferred to a nylon membrane
  5. Nylon membrane with DNA fragments positioned exactly as they were on the gel
  6. A radioactive DNA probe is added to the membrane where it binds to specific fragments (Using complementary DNA pairing)
  7. X-ray film is placed next to the membrane to detect the radioactive pattern (Developed X-ray film shows DNA fragments that combined with radioactive probe; only this is visible)
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15
Q

Describe the procedure of Gel Electrophoresis. (4)

A
  1. Place sample in wells
  2. Add standards for comparison to other wells
  3. An electric field (voltage) is applied across the gel
  4. Because DNA is a charged, it will migrate across the gel from negative to positive pole. Different sized DNA migrate at different rate. Hence, separation occurs
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16
Q

Describe the procedure of Capillary Gel Electrophoresis. (6)

A
  1. Gel is inside a capillary tubing
  2. Voltage applied
  3. Sample enters cathode (negative terminal)
  4. Travels across the tubing
  5. After passing a certain point, it will be detected with UV light (DNA fragments absorb UV)
  6. See different peaks according to the different fragments
17
Q

What is the relationship between RFLP and electrophroresis?

A

Electrophoresis is a part of RFLP to separate DNA fragments into bands.

18
Q

What does Polymerase Chain Reaction (PCR) do?

A

Allows a specific region of DNA to be repeatedly duplicated, to make enough of the target DNA region that it can be analyzed or used in some other way

19
Q

What is the advantage of PCR?

A

Can analyse very small amounts (36 cells), such as saliva from cigarette ends, back of stamps, barely visible blood stains etc

20
Q

Describe the procedure of PCR.

A

1) Double stranded DNA is heated at 94ºC. It breaks down into separate strands
2) Heat at 60ºC and add primers (short-lengths of DNA) CAGA and CCGA. Because of complementary base pairing, they will bind to the specific regions of the original DNA that they recognise
3) At 72ºC, add DNA polymerase enzyme, and add G, A, T and C. (Enzyme will build DNA polymer from nucleotides and pick up where the primers are. Add nucleotides G, A, T, C to maintain complementary base pairing across the whole strand)
4) Creates exact copies of the original DNA strands
5) Keep repeating this process (30 times)

21
Q

What are Short Tandem Repeats?

A

It is what we are looking for in the junk DNA. A method of determining an individual’s DNA profile by counting the number of times a small DNA sequence (short tandem repeat unit) is repeated at a specific chromosomal location.

22
Q

What is multiplexing?

A

Simultaneous analysis of multiple STRs (using multiple probes). Using more STRs = higher probability of having something unique

23
Q

How does STR and Capillary Gel Electrophoresis work?

A

DNA fragment is detected in pairs, where one is from mother and one is from father.

24
Q

How does Paternity & Maternity testing work?

A

It determines from where did you get your STRs. Nature randomly selects one from each pair from father, then one from each pair from mother. Child’s STRs must match both parents completely

25
Q

What happens when the STR from mother and father is the same?

A

it becomes a big single peak during Capillary Gel Electrophoresis.

26
Q

Do siblings share the same STR? How do we verify if two people are siblings?

A

Some STR of siblings will match, some do not. Only identical twins have exactly the same DNA.

To verify if two people are siblings, compare both their DNA to their parents

27
Q

How are DNA databases utilised? (3)

A

Many countries have databases of DNA of known criminals (DNA from crime scene)

  1. Can also be used in cold cases if the evidence has been preserved
  2. Finding DNA with unusual features and matching it to people in the database, and investigating his family group
  3. Private DNA databases also exists, for genealogy (finding one’s long lost family member etc)
28
Q

What is Mitochondrial DNA (mtDNA)?

A

A circular genome located the mitochondria

29
Q

What are 5 differences between mtDNA and nuclear DNA?

A

1) Only has 16569 bases
2) Non-coding region (D-loop) exhibits variation between unrelated individuals of about 1-3% (Can use for profiling)
3) Higher copy number per cell; more resistant to sample degradation than nuclear DNA
4) mtDNA inherited strictly from mother. Not unique to individual: similar to one’s mother, grandmother etc
5) Faster mutation than nuclear DNA

CM5002 Forensic Science (10 decks)

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