Figure 2.

Distance from an origin may affect telomere length. Telomere-proximal origins are inhibited from firing and can be passively replicated by adjacent origins. Here, Ori 1 is efficient, while Ori 2 does not fire in every cell cycle. If telomerase travels with the fork that initiates at Ori 1, the probability of it reaching the end is relatively low. In contrast, if Ori 2 fires, there is a shorter distance to the chromosome end, and telomerase has a high probability of elongating that telomere. Rif1 normally blocks the telomeric Ori 2 from firing; in the absence of Rif1, Ori 2 will fire, and telomeres will elongate.