In their review Dodge and Vickerman (1980) differentiate four types of
mitosis.
- Closed mitosis with internal division spindle. In this case all
the time the nuclear envelope remains intact, and the dividing apparatus
is located within the nucleus. This type of mitosis is characteristic of a
number of prokaryotes, unicellular algae, euglena, paramecia, etc. Up to
now no fibres (microtubules), forming a division spindle, are observed in
them. - Close mitosis with external division spindle. In this type of
division, from the very beginning of the process fascicles of microtubes
are formed on the one side of nucleus. After that, they through channels
and tunnels penetrate in the nucleus, and the chromosomes attach to
them. No centrioles or polar small bodies are observed. During
anaphase the nucleus elongates and the chromosomes are separated,
without any break down of the nuclear envelope. It is observed in
different species of free-living and parasitic dinoflagellates. - Semi-open mitosis. In this case, the nuclear envelope remains
substantially intact, but the gaps or polar fenestrae developed in it make
possible the intervenrtion of cytoplasmic mitotic centres in the processes
of nuclear division. Such type of mitosis is described in different species
of green algae and fungi. In some of them one can already observe
centrioles or polar small bodies and small kinetochores through which
the chromosomes attach to the microtubules, and also shapely nucleoli.
The very mitosis is realized with spiralizing the chromosomes, break
down of the nucleolus, and inside the nucleus a structure resembling
division spindle appears. During anaphase the chromosomes are
distributed, the nucleus elongates, followed by dividing in two. The old
nuclear envelope can breaks down and participate in the building nuclear
envelopes of the newly obtained nuclei.- Open mitosis. This is the main type of division in higher
eukaryotes. Naturally there are some differences in the individual plant
and animal organisms, related to the organization of dividing structures.
A peculiarity is, that in all cases the nuclear envelope break down
already at the time of prometaphase and then the processes are realized
openly in cytoplasm.
Using the results of the investigations made on different prokaryotic
and eukaryotic organisms described in the literature, Alberts et al. (1986)
have made a scheme, illustrating some stages of the mitotic spindle (Fig.
3–14).
One variety of mitosis is meiosis called also reducing division. It is
observed by forming the mature sexual cells in higher plant and animal
organisms, normally having in their vegetative cells a diploid set of
chromosomes obtained as a result of fertilization. Its biological essence
lies in transforming diploid nucleus (2n) in haploid (1n) one, and
- Open mitosis. This is the main type of division in higher