Biology - Autoradiography
* The membrane is exposed to X-ray film if the probe has radio-active
* The presence of the marker and therefore of the probe is shown where
the film turns dark
* If the probe has a fluorescent marker, this can be detected by the
emission of a yellow light. The target DNA sequence has been identified.
* Any DNA not hybridised can be removed chemically, isolating the target
In a similar manner electrophoresis can be used to separate fragments of
RNA or proteins.
The method above describes how segments of DNA are located outside cells.
Probes can be used to detect particular segments of DNA along a chromosome
within cells. The cells are treated (by heat or chemically) to denature the
chromosomes  and fluorescent probes are added. The probes will hybridise
with the target DNA. This technique is referred to as fluorescent in situ
hybridisation or FISH (in situ means 'in place').
Gene probes  can be used to detect the presence or absence of alleles
leading to genetic disorders  such as sickle cell anaemia, Duchenne
muscular dystrophy and many more.
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