The three major troponin I isoforms are encoded by separate genes and are expressed in a muscle-type-specific manner. A human cardiac troponin I cDNA has recently been isolated and used to establish the genomic location of the cardiac troponin I gene locus (designated TNNC1). By somatic cell hybrid analysis, the locus for TNNC1 maps to human chromosome 19 and can be localised to the region p13.2-q13.2.