Gene probes and medical diagnosis

Question 1

what are DNA probes? (3 mark answer)

Answer 1

• Short, specific sequence of nucleotides
• complimentary to base sequence of target allele
• With a label attached

Question 2

What are the two most common types of DNA probe label?

Answer 2

Radioactivity

Fluorescence

Question 3

How is radioactivity detected?

Answer 3

Using x-ray film

Question 4

How is fluorescence detected?

Answer 4

Using UV light

Question 5

What is the first stage of using DNA probes?

Answer 5

The DNA sample is digested using restriction enzymes and separated using gel electrophoresis

Question 6

What is the second stage of using DNA probes?

Answer 6

• The separated strands are transferred to a nylon membrane and incubated with fluorescently labelled DNA probes
• If alleles are present, the DNA probe will then hybridise to it

Question 7

What is the third stage of using DNA probes?

Answer 7

The membrane is exposed to UV light and if the gene is present, the sample will fluoresce

Question 8

What is a microarray used for?

Answer 8

To screen for multiple alleles at the same time

Question 9

What are the steps involved in microarray?

Answer 9

• Fluorescent labelled DNA probes are washed over the array
• If there are any DNA sequences that match any probes, then they will stick to the array
• The array is then washed to remove any unbound probes
• Placed under UV light and any DNA probes which are bound will fluoresce, showing the person has the allele

Question 10

What are some uses of screening with DNA probes?

Answer 10

• Identify inherited conditions
• Determine how a patient will respond to specific drugs
• Identify health risks
• Genetic counselling - advising patients and relatives about the risks of genetic disorders
• Personalised medicine