Cells were labeled with BrdU.The leftmost panel was stained with propidium iodide to identify bulk DNA.The right panel was stained using an antibody to BrdU to identify replicating DNA.

• 区分独立复制子与熔化眼的常用方法是依靠DNA的伸直，因为在其中几个复制子能够发现具有活力，假设当所有的复制子在相同时间内已经起始时在同一状态时被观察，但必须在连接单位的复制叉相遇之前。