Figure 1
APS/Alan Stonebraker

Figure 1: (Top) As cells age, telomeres (the protective ends of chromosomes) are subject to two driving forces that determine their length: each replication leads to telomere shortening, but in cells like germ or stem cells, the action of the enzyme telomerase adds DNA stretches to the telomeres. (Bottom) Telomere length as a function of time: The length evolution can be described as a “biased” random walk, arising from the fact that lengthening and shortening probabilities vary with the length of the telomere: short telomeres tend to get longer, while long telomeres become shorter. The telomere length distribution reaches a steady state after a certain number of cell divisions.