In Situ Hybridization

ISH (In situ hybridization) uses a complementary strand of DNA to localize a specific DNA sequence in a tissue or onto a specific location on a chromosome. ISH is possible because of DNA's ability to hybridize, or anneal, to its complementary strand at the correct temperature. The DNA probe is fluorescently label (Fluorescent in situ hybridization or FISH) or it may be detected through autoradiography if the probe is radioactively labelled.

Process
Sample cells are treated to increase their permeability and allow the hybribization of the probe. A complmentary probe is created with a radioactive or fluorescent label. The probe is added to the treated cells and allowed to hybridize; excess probe is washed away. Autoradiography, immunochemistry, or fluorescence microscopy is used to detect the probe's location.

Applications
ISH can be used to determine the structure, function, and evolution of chromosomes. It is used in chromosomal gene mapping or to determine the expression of genes.