Green fluorescence protein (GFP) is derived from the jellyfish Aequorea victoria, which emits green light (emission peak at a wavelength of 509 nm) when excited by blue light (excitation peak at a wavelength of 395 nm). GFP fluorescence is stable under fixation conditions and suitable for a variety of applications. It has been widely used as a reporter for gene expression, enabling researchers to visualize and localize GFP-tagged proteins within living cells without chemical staining.