Often, a particular piece of DNA (or RNA) of interest needs to be detected in a mixture containing many pieces with different sequences.
One way to do this is by hybridisation. Hybridisation refers to the process in which two complementary pieces of DNA (or a piece of DNA and a piece of RNA) anneal to form a double-stranded molecule.
The piece of DNA or RNA used to detect complementary sequences is often called a probe. If the probe is ‘labelled’, for example by making it radioactive or fluorescent, then any pieces of DNA or RNA that it hybridises to will also be labelled and can be detected.
Before it can be used for hybridisation, a double-stranded DNA molecule must be separated into single-stranded DNA molecules, or denatured. Denaturing is usually achieved by heating the sample; when it is cooled, the resulting single-stranded molecules will hybridise to complementary molecules in the mixture, including those of the labelled probe.
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