Amitosis is also called Karyostenosis, which is a type of direct cell division.
The name ‘Amitosis’ was given by Remake and the explanation of amitosis was given by Walther Fleming in 1880 and others. It is the most primitive type of cell division.
Condensation of chromosomes does not occur in amitosis means the chromatin network, which is initially present in the form of long threads does not condense to form distinct structures which are called chromosomes.
In amitosis, chromosomes are not visible during the division process. It is a process of division without recognizable chromosomes. In this process, spindle fiber formation does not take place.
The division of the nucleus is direct, that is without sequential changes (prophase, metaphase, anaphase, telophase). During amitosis, the division of cytoplasm and nucleus occur simultaneously by constriction.
In amitosis, the division may be equal or unequal. Amitosis is the fastest cell division process, which may complete 20-30 minutes. Amitosis is the cell division of prokaryotes. But exceptionally also occurs in some eukaryotes- Yeast (Budding occurs by amitosis).
Examples of amitosis
Amitosis usually occurs in:
- In Amoeba, multiple fission occurs by amitosis.
- In Paramecium, division of meganucleus.
- Budding in Yeast occurs by amitosis.
- Seen in the cells grown from placental tissue in rats
- In mammals – Growth of fetal membranes (amnions, chorion, allantois, yolk sac)
- During the division of mitochondria and chloroplast.