Titia de Lange, et al., Structure and Variability of Human Chromosome Ends, Molecular and Cellular Biology 10, 1990,
The minimal size of the subtelomeric repeat is 4 kilo bases (kb); it shows a high frequency of restriction fragment length polymorphisms and undergoes extensive de novo methylation in somatic cells. Distal to the subtelomeric repeat, the chromosomes terminate in a long region (up to 14kb) that may be entirely composed of TTAGGG repeats. This terminal segment is unusually variable. Although sperm telomeres are 10 to 14kb long, telomeres in somatic cells are several kilo base pairs shorter and very heterogeneous in length.