What is one requirement of Fluorescent In Situ Hybridization (FISH)?

Fluorescent In Situ Hybridization (FISH) requires a labeled DNA fragment as a probe to visualize specific nucleic acid sequences within fixed cells or tissue sections. This labeling is typically done with fluorescent dyes, which allow the probe to emit light when excited by a certain wavelength, thus enabling the identification and localization of specific DNA or RNA sequences.

This feature is fundamental to FISH, as the labeled probe binds to its complementary target sequence, revealing information about the genetic material. This technique is widely used in clinical diagnostics, particularly for detecting chromosomal abnormalities and pathogens, as well as in research contexts to study gene expression and chromosome organization.

The other options do not accurately represent essential requirements of the FISH technique. For instance, the probes used can be synthetic DNA, RNA, or even PNA (peptide nucleic acid), and they do not have to be in solid supports, nor are restriction enzymes required for the hybridization process. Thus, the emphasis on a labeled DNA fragment authentically captures one of the critical aspects of FISH methodology.