Figure 4.

Possible scenarios of origin stalling within a chromosome and at a telomeric region. Stall events may occur either within the chromosome (A) or at the telomeric region (B). One-side stall event (a) does not endanger replication if it happens within the chromosome – DNA will be replicated by another active fork. If, unlikely, active forks stall on 2 sides of yet unreplicated DNA (a'), part of the DNA between them cannot be replicated and replication partially fails, but if there is a dormant origin between (a”), it is activated (blue highlight) and can finish the replication. At the telomeric chromosome end there must be a dormant ‘emergency’ origin that become activated in case of stalling (b). If not, DNA from a telomeric region cannot be replicated (b').