Definition: Fluorescent In-situ hybridization

Explanation: The detection of nucleotidic sequences on a combed DNA molecule is peformed indirectly, by first hybridizing the seeked nucleotidic sequences (the probes) with the combed DNA (also called the matrix DNA or target). If the probes are synthesized with incorporated fluorescent molecules or antigenic sites which can be recognized with fluorescent antibodies, the direct visualisation of the relative position of the probes is possible. This is the goal of physical mapping. The hybridization step consists in simply mixing the single strand probes with the denaturated target DNA (the combed molecules). Denaturation of the DNA is obtained by heating the DNA, which separates the two strands, and allows access of the single strand probes to their respective complementary combed single strand. The detection of the probes is the final step of fluorescent in situ hybridization. It consists in recognising the probes with fluorescent antibodies corresponding to the antigenes incorporated in the probes .