B6. Gene Probes and Medical Diagnosis Flashcards
Locating alleles using DNA probes
What are DNA probes used for? (2)
What are DNA probes? (3)
What does it have? (2)
- DNA probes can be used to locate specific alleles of genes (e.g. on chromosomes) or to see if a person’s DNA contains a mutated allele that causes a genetic disorder.
- DNA probes are short strands of DNA. They have a specific base sequence that’s complementary to the base sequence of part of a target allele (the allele you’re looking for, e.g. an allele that causes a genetic disorder).
- This means a DNA probe will bind (hybridise) to the target allele if it’s present in a sample of DNA
- DNA probe also has a label attached, so that it can be detected. The two most common labels are a radioactive label (detected using X-ray film) or a fluorescent label (detected using UV light)
Figure 1: A DNA probe.
Locating alleles using DNA probes (3 Steps)
- A sample of DNA is digested into fragments using restriction enzymes and separated using electrophoresis
- The separated DNA fragments are then transferred to a nylon membrane and incubated with a fluorescently labelled DNA probe. If the allele is present, the DNA probe will bind (hybridise) to it
- The membrane is then exposed to UV light and if the gene is present there will be a fluorescent band.
Screening for multiple genes
What can the probe be used for and what can this do?
What is a DNA microarray?
How does it work (4 steps)
- The probe can be used as part of a DNA microarray, which can screen for lots of different genes at the same time.
- A DNA microarray is a glass slide with microscopic spots of different DNA probes attached to it in rows.
- A sample of fluorescently labelled human DNA is washed over the array.
- If the labelled human DNA contains any DNA sequences that match any of the probes, it will stick to the array.
- So this means you can screen the DNA for lots of different mutated genes at the same time.
- The array is washed, to remove any fluorescently labelled DNA that hasn’t stuck to it, and then visualised under UV light. Any labelled DNA attached to a probe will show up
Any spot that fluoresces means that the person’s DNA contains that specific allele.
Figure 4: Diagram of a DNA microarray
Tip: If a radioactively labelled probe is used, the fragments are transferred to X-ray film. If the gene and probe are present, a …
Tip: If a radioactively labelled probe is used, the fragments are transferred to X-ray film. If the gene and probe are present, a shadow will form on the film.
Tip: Microarrays aren’t just used to diagnose genetic diseases. Researchers can use them to analyse other ____samples, or even to analyse ______ samples.
Tip: Microarrays aren’t just used to diagnose genetic diseases. Researchers can use them to analyse other DNA samples, or even to analyse mRNA samples.
Uses of screening with DNA probes
3 uses?
1 problem?
- It can be used to help identify inherited conditions.
- It can be used to help determine how a patient will respond to specific drugs.
- It can also be used to help identify health risks.
However, some people are concerned that genetic screening may lead to discrimination by insurance companies and employers if people are known to have a high risk of developing a condition.
Genetic counselling
The results of screening can be used for genetic counselling. Genetic counselling is advising patients and their relatives about the risks of genetic disorders.
It involves advising people about _________(e.g. looking for mutated alleles if there’s a family history of cancer) and explaining the results of a screening.
Screening can help to identify if someone is the ________ of a _________ ________, the type of mutated allele they’re carrying (indicating the type of genetic disorder or cancer) and the most effective treatment.
If the results of a screening are positive (an individual has the mutation) then genetic counselling is used to advise the patient on the options of ___________ or ___________ available
The results of screening can be used for genetic counselling. Genetic counselling is advising patients and their relatives about the risks of genetic disorders.
It involves advising people about screening (e.g. looking for mutated alleles if there’s a family history of cancer) and explaining the results of a screening.
Screening can help to identify if someone is the carrier of a mutated allele, the type of mutated allele they’re carrying (indicating the type of genetic disorder or cancer) and the most effective treatment.
If the results of a screening are positive (an individual has the mutation) then genetic counselling is used to advise the patient on the options of prevention or treatment available
Personalised medicine
The results of screening can also be used in personalised medicine. Your genes determine how your body responds to certain drugs. Different people respond to the same drug in different ways-which makes certain drugs more effective for some people than others. This is where personalised medicines come in. Personalised medicines are medicines that are tailored to an individual’s ____. The theory is that if doctors have your genetic information, they can use it to _________ how you will respond to different drugs and only prescribe the ones that will be most effective for you.
The results of screening can also be used in personalised medicine. Your genes determine how your body responds to certain drugs. Different people respond to the same drug in different ways-which makes certain drugs more effective for some people than others. This is where personalised medicines come in. Personalised medicines are medicines that are tailored to an individual’s DNA. The theory is that if doctors have your genetic information, they can use it to predict how you will respond to different drugs and only prescribe the ones that will be most effective for you.
