The C-Src gene is closely related to the viral-sarcoma gene (V-SRC) present in certain cancer-causing retroviruses. The normal cellular gene, C-Src, was first discovered in chickens in the late 1970s by American scientists J. Michael Bishop and Harold E. Varmus. Its detection marked a tremendous breakthrough in cancer research and triggered a major shift in the modern understanding of the disease. Before the discovery, cancer was generally believed to result from invasion by a viral gene foreign to normal cells, but the existence of C-Src demonstrated that a gene normally present in the cells themselves can induce tumors. In the digital video sequences presented in this section, C-Src is fluorescently labeled with m-Emerald and H2B is shown tagged with mApple.