Modes and Types of Cell Division
Section 3.4.
As it was mentioned in Section 3. 1, evolution has created
different modes and types of cell division, preserving its basic
predestination as a mechanism of reproduction of living organisms. Their
variety is so great, that it is difficult to be ranged over and explained
thoroughly. Essentially they can be reduced to two basic modes:
1. Direct division or amitosis.
2. Indirect division or mitosis.
There are reasons to suppose, that in evolutionary aspect the direct division
has preceded mitosis. But because of the combination of historical
circumstances, indirect or mitotic division is better investigated and is more
widely recognized in cytology than the amitotic. One of the reasons for that is the
fact, that during mitosis well-expressed chromosomes and dividing structures
are formed. They are easily observable under light microscope and long ago
focus the attention of researchers, while during amitosis they are lacking or not
yet established. Amitosis is put aside, and its importance is not appreciated
properly.
image
Figure 3–7. Electron micrograph of a bacterial cell during the process of division (Courtesy of S. C. Holt; From Swanson and Webster, 1980).
Direct division or amitosis is a basic mode of division in prokaryotic cells, which is realized without
formation of well-expressed dividing structures (Fig. 3–7). For the first time amitotic division is described by
Remak (1858), and the term “amitosis” is proposed by Flemming (1882) in order to distinguish from the
indirect division or mitosis, already known at that time. Except in prokaryotes there are data on amitotic
division of nuclei in cells of different tissues and organs in higher organisms (see Hessin, 1967).
Some authors doubt the existence of amitosis, others consider it defective mode of division, still others
deny it completely considering it an alternated mitosis. Possibly these
greatly differing viewpoints have incited Bucher (1958) to entitle his article “Does the
amitosis exist?” in which he definitely accepts the possibility of adequate nuclear
division in this way. If accept that amitosis is a process of division without forming the
characteristic of eukaryotic cell mitotic chromosomes and division spindle, which serve
as instruments for distribution of the genetic material in daughter cells, it can be
considered a really existing mode of cell division in the prokaryotic cells, whose
mechanisms are not clearly explained.