In prokaryotes, binary fission is used for the purpose of asexual reproduction. Prokaryotes include bacteria and archaebacteria. The parent cell divides into two parts that will eventually grow to the size of the parent cell. The single DNA molecule is replicated first. The original and copied DNA separate from eachother and attach to different parts of the cell. Then, the cell membrane pulls apart and the DNA and its replicate become enclosed in one of the new cells that forms. The cells that are produced are smaller than the original parent cell with the same genetic material as the parent cell. Therefore, in a colony that came from one cell originally, all the other cells are clones of the original.
Since prokaryotic organisms lack membrane bounded nucleus, they are incapable of nuclear division processes that would be expected of eukaryotic mitosis or meiosis. Therefore, they simply duplicate their genetic material, or DNA, and then divide into two parts (cytokinesis), each part receiving one copy of DNA. "Binary fission is a primary method of reproduction for prokaryotic organisms" (Encyclopedia Britannica).