Definition: DNA FISH probes

Explanation: FISH is a laboratory technique used to determine how many copies of a specific segment of DNA are present in a cell. It is also used to identify structurally-abnormal chromosomes. In the lab, a segment of DNA is chemically modified and labelled so that it will look fluorescent (very brightly colored) under a special microscope. This DNA is called a "probe." Probes can find matching segments of DNA when added to cells under certain conditions.