Module 8 - Gene probes, genetic fingerprinting and medical diagnosis

Question 1

6 msrks

Describe how genetic fingerprinting is carried out.

Answer 1

1 DNA extracted from sample
2 DNA cut using restriction enzymes
3 must leave VNTRS / required core sequences intact
4 DNA fragments separated using electrophoresis
5 detail of process e.g. mixture put into wells on gel and electric current passed through
6 immerse gel in alkaline solution / two strands of DNA separated
7 Cover with nylon to absorb DNA
8 DNA fixed to nylon / membrane using uv light
9 radioactive marker / probe added (which is picked up by required fragments) / complementary to VNTRS
10 (areas with probe) identified using X-ray film / autoradiography

Question 2

Explain genetic fingerprinting

Answer 2

1. Collect the DNA and use PCR to amplify it.
2. Restriction endonucleases are used to hydrolyse the DNA.
3. Use gel electrophoresis to separate the DNA fragments.
4. The DNA fragments are separated based on charge with smaller fragments of DNA moving faster and further.
5. The DNA should be treated with an alkali to make it single stranded.
6. The DNA probes can then be added and would hybridise with the DNA fragments.
7. Wash away excess probes which did not bind.
8. The probe would have fluorescence or a radioactive tracer bound to it.
9. Use UV light or an audioradiography to determine if the gene/allele/VNTR is present.

Question 3

6 marks

Describe how the technique of genetic fingerprinting is carried out and explain how
it can be used to identify a person, such as Saddam Hussein.

Answer 3

1. DNA is cut
2. using restriction enzyme
3. electrophoresis
4. separates according to length / mass / size
5. DNA made single-stranded
6. transfer to membrane / Southern blotting
7. apply probe
8. radioactive / single stranded / detected on film / fluorescent
9. reference to VNTRs
10. pattern unique to every individual

Question 4

1 mark

What is a DNA probe?

Answer 4

1. Short, single strand of DNA
2. Bases complementary with DNA

Question 5

1 mark

The DNA on the nylon membrane is treated to form single strands. Explain why.

Answer 5

So DNA probe binds/anneals

Question 6

2 marks

The soybean cells were screened for the presence of the P34 protein. This process involved the use of gel electrophoresis to separate proteins extracted from soybean cells.
Suggest two features of the structure of different proteins that enable them to be separated by gel electrophoresis.

Answer 6

1. Mass/number of amino acids/polypeptides
2. Charge
3. R groups differ

Question 7

3 marks

Explain why it takes longer to obtain a genetic fingerprint if the sample is
(i) very small
(ii) contaminated

Answer 7

1. i) PCR is needed
2. ii) other DNA present
3. Need to identify ‘required’ DNA from rest

Question 8

2 maarks

The length of the replicated DNA fragment is different for each species.
Explain why this is important in identifying the species involved.

Answer 8

1. Primer has different DNA sequence
2. DNA specific / complementary base-pairing

Question 9

2 marks

Name two techniques the scientists may have used when analysing viral DNA to determine that the viruses were closely related.

Answer 9

• The polymerase chain reaction
• Genetic fingerprinting
• Gel electrophoresis
• Genome sequencing