Most students learn that bacteria separate their chromosomes as part of the process of binary ssion and eukaryotes separate their chromosomes by mitosis or meiosis followed by cytokinesis (cell division). However, seldom do they learn that there are many other variations on these three themes. First, the basics will be described and then all of the other variations will be explained. Together, it indicates the diversity in the replication and partitioning of chromosomes, but it also illustrates some of the evolutionary steps in the process of replication and separation of chromosomes. In bacteria, the chromosomes are attached to the cell membrane by specic proteins. As replication and cell division are initiated, these proteins double, thus attaching the replicating chromosome to the membrane in two places (see Chapter 6, Figure 6.2). These proteins then begin to migrate toward opposite poles of the growing bacterial cells. By the time the chromosome has been completely replicated, the proteins are at opposite poles and, as the cell grows, the chromosomes are pulled apart completely, which leaves one complete chromosome on each side of the cell as the two cells are pinched apart to form the two daughter cells.