21.1 DNA Profiling

Question 1

What is a genome?

Answer 1

All the genetic material of an organism.

Question 2

What is an exon?

Answer 2

Regions of DNA that code for proteins.

Question 3

What is an Intron?

Answer 3

Regions of non-coding DNA or RNA.

Question 4

What is a telomere?

Answer 4

Structure at the end of a chromosome.

Question 5

What is a centromere?

Answer 5

Region at which two chromatids are held together.

Question 6

What is satellite DNA?

Answer 6

Short sequences of DNA that are repeated many times within the introns, telomeres, and centromeres.

Question 7

What is a mini-satellite?

Answer 7

A sequence of 20-50 base pairs repeated 50+ times (aka variable number tandem repeats - VNTRs)

Question 8

What is a micro-satellite?

Answer 8

A small region of 2-4 bases repeated 5-15 times (aka short tandem repeats -STRs)

Question 9

What is DNA profiling?

Answer 9

Producing an image of the patterns in the non-coding DNA of an individual.

Question 10

What is the first stage in the process of producing a DNA profile?

Answer 10

Extracting the DNA.

Question 11

Where must the DNA be extracted from?

Answer 11

A tissue sample.

Question 12

What technique or process is used when extracting DNA?

Answer 12

Polymerase Chain Reaction (PCR).

Question 13

What is the polymerase chain reaction (PCR)?

Answer 13

A process by which a small sample of DNA can be amplified using specific enzymes and temperature changes.

Question 14

Summarise in simple words, step 1 of producing a DNA profile.

Answer 14

DNA is extracted from the sample.

Question 15

What is the second stage in the process of producing a DNA profile?

Answer 15

Digesting the sample.

Question 16

What enzyme is used when digesting the sample?

Answer 16

Restriction endonucleases.

Question 17

What is restriction endonucleases?

Answer 17

Enzymes that chop a DNA strand into lots of small pieces.

Question 18

What is the restriction site or recognition site?

Answer 18

A specific nucleotide sequence the different restriction endonucleases cut DNA at.

Question 19

How many cuts do all restriction endonucleases make?

Answer 19

Two, once through each strand of the DNA double helix.

Question 20

What do restriction endonucleases give scientists the ability to do?

Answer 20

Cut DNA strands at defined points in the introns, leaving repeat units or satellites intact and a mixture of mini- and microsatellite regions intact at the end.

Question 21

Summarise in simple words, step 2 of producing a DNA profile.

Answer 21

Restriction endonucleases cut the DNA into fragments.

Question 22

What is the third stage in the process of producing a DNA profile?

Answer 22

Separating the DNA fragments.

Question 23

What technique or process is used to separate the DNA fragments?

Answer 23

Electrophoresis.

Question 24

What is electrophoresis?

Answer 24

A type of chromatography that relies on the way charged particles move through a gel under the influence of an electrical current. Used to separate nucleic acid fragments.

Question 25

Why is the gel, in step 3 of producing a DNA profile, immersed in an alkaline buffer after running in electrophoresis?

Answer 25

Denature DNA fragments causing strands to separate into single strands and expose the bases.

Question 26

In electrophoresis, why is the agarose gel placed into a buffering solution?

Answer 26

To maintain and prevent a decrease in pH as pH can denature enzymes.

Question 27

What is the purpose of a DNA ladder?

Answer 27

Compare fragments of DNA to known values.

Question 28

What is a DNA ladder?

Answer 28

A set of standards that are used to identify the approximate sizes of a molecule run on gel in electrophoresis.

Question 29

What does the rate of movement depend on within an agarose gel?

Answer 29

The length of DNA fragments. Small fragments with less base pairs move faster.

Question 30

What is southern blotting?

Answer 30

Transferring separated strands to nitrocellulose paper or nylon membrane placed over the gel. The membrane or paper is covered with several sheets of dry absorbent paper to draw the alkaline solution containing DNA up by capillary action. Single-stranded DNA is transferred to the paper or membrane as they are unable to pass through and is then fixed with UV light or heating to 80°C.

Question 31

Summarise in simple words, step 3 of producing a DNA profile.

Answer 31

Fragments are separated using gel electrophoresis. DNA fragments are transferred from the gel to a nylon membrane by the process of southern blotting.

Question 32

What is the fourth stage in the process of producing a DNA profile?

Answer 32

Hybridisation.

Question 33

What is hybridisation?

Answer 33

The addition of fluorescent or radioactive probes to DNA fragments via complementary base pairing.

Question 34

What do DNA probes identify?

Answer 34

The microsatellite regions that are more varied than the larger minisatellite regions.

Question 35

Summarise in simple words, step 4 of producing a DNA profile.

Answer 35

DNA probes are added to label the fragments. These radioactive probes attach to specific fragments.

Question 36

What is the final stage in the process of producing a DNA profile?

Answer 36

Seeing the evidence.

Question 37

How would you see the evidence if radioactive labels were added to DNA probes?

Answer 37

X-ray images are taken of the paper/membrane.

Question 38

How would you see the evidence if fluorescent labels were added to DNA probes?

Answer 38

Paper/membrane is placed under UV light so the fluorescent tags glow.

Question 39

What are the ingredients needed to carry out the Polymerase Chain Reaction (PCR)?

Answer 39

- A sample of DNA. - Free nucleotides (A,T,C,G). - DNA polymerase (Enzyme). - Primers (Complimentary to the beginning of the target sequence, like a starting point).

Question 40

What is a Polymerase Chain Reaction (PCR) machine also called?

Answer 40

Thermal Cycler.

Question 41

What is the first stage when carrying out a Polymerase Chain Reaction (PCR)?

Answer 41

Denaturation.

Question 42

What happens in the first stage of a Polymerase Chain Reaction (PCR)?

Answer 42

Temperature set to 95°C causing DNA stands to separate by the breaking of the hydrogen bonds.

Question 43

What is the second stage when carrying out a Polymerase Chain Reaction (PCR)?

Answer 43

Annealing.

Question 44

What happens in the second stage of a Polymerase Chain Reaction (PCR)?

Answer 44

Temperature decreased to 55°C to allow primers to attach (anneal) to complimentary ends of the DNA template strand.

Question 45

What is the third stage when carrying out a Polymerase Chain Reaction (PCR)?

Answer 45

Extension.

Question 46

What happens in the third stage of a Polymerase Chain Reaction (PCR)?

Answer 46

Temperature increased to 72°C to allow Taq polymerase to add complimentary bases to the template strand. (like its extending from the primers by adding bases).

Question 47

What are some uses of DNA profiling?

Answer 47

- Forensic science (Crime scenes) - Proving paternity of a child (prove or disprove family relationships) - Identifying the species to which an organism belongs to. - Demonstrate evolutionary relationships between different species. - Identifying patients who are at risk of developing particular diseases (eg. cancers and heart diseases)