Telomeres are the physical ends of eukaryotic chromosomes that in vertebrates consist of multiple copies of the sequence TTAGGG. The protective telomeres keep the chromosome ends intact, and thereby protect the underlying genes. In normal somatic cells, the telomere length shortens at each cell division, finally leading to senescence. Some cells maintain their capacity to divide due to the action of the enzyme, telomerase. Examples are germ cells, fetal cells, hematopoietic stem cells, and basal cells of the epidermis. Established tumor cell lines can divide forever and are "immortal" mainly due to reactivation of telomerase. In 80-90% of human primary tumors telomerase is reactivated. Telomerase activity and the preservation of telomere length are, therefore, important for the cancerous process. The genetically determined variation in telomerase activity between individuals makes telomere length measurements relevant for the study of age-related diseases. The telomeres of the individual chromosome arms show heterogeneity in the number of telomeric repeats.

The Telomere PNA FISH Kits are for the detection of human (or other vertebrate) telomere sequences by fluorescence in situ hybridization (FISH) using a fluorochrome-conjugated PNA probe. PNA is superior to DNA in terms of sensitivity and specificity as a coverage of 99-100% can be achieved. The probe does not recognize subtelomeric sequences allowing exact measurement of the telomere length.