Method for detecting a specific DNA sequence
A DNA sequence can be imagined as kind of a zip with the "teeth" being the bases adenine (A), cytosine (C), guanine (G), and thymine (T). The information contained in DNA is encoded in the sequence of these four letters along the strand.
"Teeth" opposite to each other form pairs, either A with T or G with C. For example, the sequence ACGCT has the complementary counterpart TGCGA.
The linear molecule can be unzipped by heating. Hybridisation refers to a process whereby short, single-stranded DNA fragments (“probes”) are introduced, which may potentially match up with sequences on one of the free, individual strands. If a complimentary sequence exists, the probe will be bound to the DNA strand upon cooling. If the probe is associated with an optical marker, the specific fragment of DNA can be visualised and identified.
Principle of hybridisation:
In practice, the DNA is bound to a filter called a blot. To make it easier for the probe to find its complementary sequence, the DNA is first cut by restriction enzymes into smaller segments. The probe is then added to the filter:
In dot-blot hybridisation, the probe solution is dotted onto the filter.
In Southern blotting, the DNA fragments are sorted by agarose or polyacrylamide gel electrophoresis and then transferred to the filter.