Genetic screening, DNA probes and microarrays
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Explainer Video
Summary
Genetic screening, DNA probes and microarrays
In a nutshell
Genetic screening is used to identify heritable conditions. Geneticists use this method to screen for specific alleles that are associated with genetic disorders. DNA probes and hybridisation can be used to locate these alleles, genetic counsellors can then use this information to advise patients.
DNA probes
Definition
DNA probes are short sections of DNA that are complementary to a specific part of a target allele. The target allele is usually one that causes a genetic disease.
DNA probes can be used to locate a specific allele within a person's genome as they hybridise (bind) to their complementary sequence. They can also identify whether or not an individual's genome contains an allele that is associated with a certain genetic disease or disorder.
There are two types of DNA probes.
Radioactively labelled probes | These DNA probes are made up of nucleotides that contain the radioactive isotope . |
Fluorescently labelled probes | These DNA probes are able to fluoresce when they have bound to the target allele. |
The process of using DNA probes to locate alleles is explained below.
| 1. | Identifying the sequence | The first step is to identify the sequence of bases on the target allele. This may be achieved through DNA sequencing or by searching existing genetic libraries. |
| 2. | Complementary DNA fragment | A complementary DNA fragment must be created that has a sequence of bases complementary to the target allele. |
| 3. | Fluorescent labelling | The DNA probe is made by attaching a label (radioactive or fluorescent label) to the DNA fragment, so it can be detected easily. |
| 4. | PCR | Using PCR, multiple copies of the DNA probe can be produced. |
| 5. | DNA hybridisation | The individual's DNA that is being tested will be heated to separate the double-stranded DNA. The separated DNA strands are cooled and mixed with probes that bind to the complementary base sequence on one of the strands. |
| 6. | Probe binding | If the DNA from the individual contains the mutated target allele one of the probes will bind to it as the probe will have complementary base sequences to the mutated allele. |
| 7. | Detection | The remaining hybridised DNA can be detected using a special microscope for fluorescent probes or using x-rays for radioactively labelled probes. The dye fluoresces (8.) at a specific wavelength of light (9.). |
Microarrays
In order to screen for multiple alleles at a time, DNA probes can be used as part of a microarray.
| 1. | A DNA microarray will have different wells that contain different DNA probes. |
| 2. | An individual's DNA is fluorescently labelled and placed over the microarray. |
| 3. | If the individual's labelled DNA contains the target mutant allele, it will bind to the DNA probes in the wells. |
| 4. | The microarray is washed to remove any unbound DNA. |
| 5. | It is the placed under a UV light and any labelled DNA will fluoresce. |
Uses of genetic screening
Genetic screening using DNA probes is very useful. Some of the applications are explained below.
Use | Explanation |
| Genetic counselling | The results of a genetic screen can identify if someone is a carrier of a disease-causing gene and ascertain the relative risk of them developing a disease. Examples
|
| Personalised medicine | Personalised medicine involves using an individual's genotype to determine how their body will respond to certain drugs. Example
|
| Lifestyle choices | Some diseases will have contributing genetic factors. Individuals can then make informed decisions regarding their health and lifestyle to minimise their risk of other risk factors. |
FAQs - Frequently Asked Questions
What is a DNA probe?
DNA probes are short sections of DNA that are complementary to a specific part of a target allele.
What is personalised medicine?
Personalised medicine involves using an individual's genotype to determine how their body will respond to certain drugs.
How are genetic screens useful?
Genetic screens are useful because the results of a genetic screen can identify if someone is a carrier of a disease-causing gene and ascertain the relative risk of them developing a disease.