What is the first step in the FISH protocol?

The first step in the FISH (Fluorescence In Situ Hybridization) protocol involves obtaining metaphase chromosome spreads or interphase cells. This step is crucial as it provides the cellular material necessary for the subsequent procedures of the FISH technique.

In order to visualize specific DNA sequences within chromosomes, researchers need to have high-quality spreads of either metaphase chromosomes, which are the condensed forms of chromosomes that are most easily analyzed, or interphase cells that still contain the genetic material of interest but in a less organized state. This initial preparation allows for the application of fluorescent probes that will bind to complementary DNA sequences during the hybridization step that follows.

Once the chromosome spreads are prepared, the next steps—denaturation of cellular DNA, specific hybridization of probes, and possibly covering parts of chromosomes—can be effectively carried out. It is essential to start with well-prepared samples to ensure accurate results in later stages of the FISH protocol.