Most students learn that bacteria separate their chromosomes as part of the process of binary fission and eukaryotes separate their chromosomes by mitosis or meiosis followed by cytokinesis (cell division). However, they rarely learn that there are many other common variations on these three themes. First, the basics will be described, and then, variations will be explained. Together, the diversity in the replication and partitioning of chromosomes illustrates some of the evolutionary steps in these processes. In bacteria, the chromosomes are attached to the cell membrane by specific proteins. As replication and cell division are initiated, these proteins double, thus attaching the replicating chromosome to the membrane in two places (see Figure 7.2). 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.