A short DNA segment that occurs only once in the human genome and whose exact location and order of bases are known. Because each is unique, STSs are helpful for chromosome placement of mapping and sequencing data from many different laboratories. STSs serve as landmarks on the physical map of the human genome.

Dr. Eric Green, of the National Human Genome Research Institute's Genome Technology Branch, defines sequence-tagged site (STS).

Related terms: base pair, chromosome, deoxyribonucleic acid (DNA), DNA sequencing, genome, Human Genome Project, mapping, physical map, polymerase chain reaction (PCR).