Yellow Fluorescent Protein (YFP) is a protein that emits a bright yellow light when exposed to specific wavelengths of light, typically blue or ultraviolet. It is derived from the jellyfish Aequorea victoria, which contains the original Green Fluorescent Protein (GFP). YFP is widely used in biological research as a marker to visualize and track proteins, cells, and other biological processes in living organisms. Researchers often use YFP in combination with other fluorescent proteins to study complex interactions within cells. Its ability to fluoresce allows scientists to observe cellular activities in real-time, making it a valuable tool in fields such as molecular biology, genetics, and biochemistry.