Abstract: A fluorescence detection apparatus is provided which has a partial reflection mirror 8 for transmitting a part of fluorescence light emitted from a fluorescent substance by projecting excitation light and reflecting the rest of the fluorescence light, and a pair of a first and a second photodiode 2,3 for measuring the light transmitted through or reflected by partial reflection mirror 8 respectively at a selected wavelength, and the pair of the first and the second diodes are arranged to be optically equivalent relative to the partial reflection mirror 8. This fluorescence detection apparatus is affected less by positional deviation of the measurement cell relative to the optical measurement system.

Abstract: A method is provided for determining the identity of a nucleotide at a preselected site in a nucleic acid molecule. The method involves the incorporation of a nucleoside triphosphate that is complementary to the nucleotide present at the preselected site onto the terminus of a primer molecule, and their subsequent ligation to a second oligonucleotide. The reaction is monitored by detecting a specific label attached to the reaction's solid phase or by detection in solution.