A gene that is coupled with a gene of primary interest when they are inserted together into a cell. The reporter gene allows identification of those few cells that have been successfully transformed or transfected by encoding a visual signal. An example of a reporter gene is that which encodes the green fluorescent protein (GFP) of the jellyfish Aequorea victoria. A minor variation of the strategy is the insertion of a gene whose product generates a visible signal, e.g. the luciferase gene from the firefly Photinus pyralis, which emits light in the presence of ATP and its substrate, luciferin. By the same strategy, the accompanying gene may allow selection of successfully transformed cells, e.g. the chloramphenicol acetyltransferase (CAT) gene, which confers resistance to chloramphenicol.