|P.364 right column 2nd paragraph: "Why So Many Replication Origins? The answers seem obvious. First, multiple origins increase the probability that a chromosome will be replicated during an S phase and thereby reduce the chance of chromosome loss at mitosis. Second, most eukaryotic cells have more DNA per chromosome than can be duplicated from a single origin in an S phase. For a human cell, the approximately 3,000,OOO kb genome is replicated in about 8 h. Since the rate at which replication forks plow through chromatin is no greater than ~ 2 kb/min [BNID 104136], bidirectional origins would need to be spaced at roughly 2000 kb intervals to finish replication in the allotted time. But this analysis, which views replication as a process that must accommodate the cell cycle rather than the other way around, underestimates the number of origins by 20-fold-the observed spacing between active origins is about 100 kb."