FIG 2.

Assignment of old and new poles and daughters in E. coli. The blue and red colors denote new and old, respectively, for both poles and daughters. Because the division plane in a rod-shaped bacterium such as E. coli cuts the cell at the midpoint of the long axis, the poles formed at the plane are new and the distal poles are old. If the polarity of the first cell is unknown, old and new poles can be determined after one division, but the assignment of old and new daughters requires two divisions. The polarity of the first cell can be determined if its genealogy can be tracked backward one or more generations. Note that the bottom four daughters are colored red and blue to designate them as old and new daughters, but their old and new poles are identified by O and N.