Finding the gene you want

Gene probes

Every gene contains a unique sequence of the four bases: adenine (A), cytosine (C), guanine (G) and thymine (T). We can test to see if a specific gene is present in a person’s genetic make-up by searching for its unique base sequence.

The search uses a gene probe, which is a piece of single-stranded DNA. The design of a probe uses the fact that when DNA strands pair up, adenine only pairs with thymine and cytosine only pairs with guanine. The base sequence on the probe matches the unique sequence in the gene that the probe is designed for.

To test a DNA sample using a gene probe, the DNA is first treated so that each of the double-stranded DNA molecules unzips into single strands. The probe is then added to the solution. Because of the way the bases pair up, the probe will attach itself only to the section of DNA that contains a base sequence that matches the probe’s sequence.

FISH, - fluorescent in situ hybridisation

Genetics Education, Murdoch Children's Medical Research Institute

Probes are constructed with a radioactive or a fluorescent section, or tag, in them, so that they can be detected after attaching to the DNA. Detecting the probe gives us information about which chromosome the gene is on, and where the gene is on that chromosome.

We know the base sequences in a number of disease-causing genes, and can find out if they are present using probes specifically designed for them.

Watch a gene probe in action - animation

Or conduct a gene probe yourself - interactive

Microarrays

Microarray, genes involved in expressing yeast protein

Genetics Education, Murdoch Children's Medical Research Institute

At any one time in a cell, some genes are switched on and working while others are switched off. To find out which genes are working and ‘expressing’ (producing copies of the gene as messenger RNA) at any one time, microarrays can be used.

Microarrays are like sets of miniaturised chemical reactions arranged on a small glass, filter, or silicon wafer. They can be used to test DNA fragments, antibodies, or proteins. A DNA microarray can take a sample and record the level of expression for every gene within that sample.

Microarrays can assist us by finding:

drugs that interact with a gene of interest
individuals with similar biological patterns
the most appropriate individuals for participating in clinical trials of new drugs

This is a tool which scientists can use to determine the function of genes and get a clearer idea of what is happening inside cells when things go wrong, as in disease.

Watch a movie to see how microarrays find out which genes are expressing.
LowRes [306K] HighRes [1,445K]

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