Gene probes + genetic counselling

Question 1

What are DNA probes?

Answer 1

• Short, single-stranded pieces of DNA that are labelled radioactively or fluorescently so they can be identified
• This is used to locate specific alleles of genes + to screen patients for heritable conditions, drug responses or health risks
• A sample of patient DNA is removed + heated to make it single-stranded
• It’s mixed with DNA probes that have been created to be complementary to a range of different alleles for genes (e.g for different diseases)
• If the patient has that allele, their DNA will bind with the probe. This can be identified using x-ray or UV light

Question 2

DNA hybridisation

Answer 2

• DNA is heated to separate the double helix into single strands + this is then mixed with complementary sequences of single-stranded DNA
• Once cooled, the DNA strand will anneal
• This method is used in medical diagnosis to identify if someone has a copy of a particular allele within their DNA

Question 3

Locating specific alleles of a gene

Answer 3

• To locate a specific allele, the DNA base sequence must be known to create the DNA probe
• This can be determined using DNA sequencing techniques
• The fragment of DNA can be produced using a gene machine
• This fragment can be amplified using PCR
• The label is then added, either a radioactive nucleotide or a fluorescent label which emits light under UV light
• After hybridisation, the DNA is washed so any unbound DNA probes are washed away
• The presence of the radioactive or fluorescence label indicates that the allele of interest is present in the patients DNA

Question 4

What is genetic screening?

Answer 4

This method can be used to screen for potential genetic disorders or for the presence of cancer using oncogenes
Its possible to screen for multiple diseases simultaneously using an array, where multiple different DNA probes are attached

Question 5

Describe an advantage of having your DNA screened

Answer 5

• Personalised medicine
• Certain drugs are more or less effective depending on your genotype. It can also help determine the best dose, which increases the effectiveness, safety + can save money

Question 6

Genetic counselling

Answer 6

• Having DNA screened is a decision that must be thought through carefully + must be discussed with patients so they can make an informed decision
• Genetic counselling is like a type of social work where people can have their family history researched to consider the likelihood of them carrying any alleles linked to diseases before starting a family or for their general health