Probes

Question 1

Describe what a DNA probe is?

Answer 1

Short strands of DNA with a specific base sequence which is complementary to the base sequence of part of the target allele meaning it will bind if target allele is present.

Question 2

How is a probe detected?

Answer 2

Can be labelled with a fluorescent label which can be detected using UV light or radioactive label which is detected using X-ray film.

Question 3

What is DNA hybridisation?

Answer 3

A section of DNA or RNA is combined with a single complementary strand.
- double strand must be separated by heating to break hydrogen bonds between complementary base pairs

Question 4

Describe how a specific allele of a gene is located using probes?

Answer 4

• sequence of nucleotides in mutant allele must be determined using DNA sequencing techniques
• DNA fragment is produced which has sequence of babies complementary to the mutant allele
• multiple copies of the DNA probe are produced using an amplification technique (PCR) + marker attached
• DNA from suspected individual must be heated to separate the double strand and is then cooked in mixture containing probes
• DNA is washed clean off any unattached probes if mutants allele present some probes will have hybridised with the DNA
• will fluoresce if allele present

Question 6

Name a method in which different genes can be screened for at the same time

Answer 6

DNA microarray which is a glass slide with different DNA probes attached to it in rows

Question 7

Describe how different genes can be screened for at the same time?

Answer 7

• sample of fluorescent key labelled DNA is washed over the microarray
• if labelled DNA contains any base sequence which is complementary to the probe it will anneal
• array is washed to remove an unattached DNA and then shone under UV light to identify which specific alleles the DNA contains

Question 8

Name three uses of screening with DNA probes

Answer 8

• Helping to identify inherited conditions
• Help identify potential health risks e.g particular mutant alleles increase risk of developing cancer
• Determine of a patient will respond to a specific drug e.g some drugs only effect against specific types of disease caused by a specific mutation

Question 9

What is genetic counselling?

Answer 9

Advising patients and their relatives about the risks of genetic disorders, involves advising people about screening and explaining results.

Question 10

What is personalised medicine?

Answer 10

Medicines that are tailored to an individuals DNA

• the genes of an individual determine how the body responds to a drug to allows doctors to prescribe most effective drugs by predicted how your body will repond

Question 11

How are different alleles located using probes?

Answer 11

DNA is digested into fragments using restriction enzymes and separated using gel electrophoresis

Fragments then transferred to a nylon membrane and incubated with fluorescently labelled probe
- if allele present probe will anneal to it

Membrane exposed to UV light and fluorescent band will appear on the DNA fragments where which contains the allele