Biology notes topic Mitosis of zoology.
Watter Fleming (1878) a German biologist was the first to study the cell division. It involves equal division of the nucleus followed by equal division of cytoplasm hence is also called " equational division". Mitosis commonly occur in somatic cell of the body.
Karyokinesis occur by following stages-
# Interphase
# Prophase
# Metaphase
# Anaphase
# Telophase
Interphase - when the cell is not in division stage it's nucleus is said to be in Interphase or metabolic state. Nucleus has a definite nuclear wall. The karyolymph is very dense with one or more nucleolus and inconspicuous chrmatic reticulum in it.
Prophase- the nuclear reticulum and nucleoli become clear due to dehydration of the nuclear sap at this stage. The chromatic network dissociates and the chromosome become distinct. The two chromatic lie closely parallel and are still connected with each other at a single point called centromere. The nucleolus begins to disappear and simultaneously the matrix sheaths appear around the chromosomes. The centrioles move and come to lie on two opposite side of the nucleus.
Metaphase- the beginning of Metaphase is marked by the dissolution of nuclear membrane and simultaneous appearance of spindle fibres. The chromosome at this stage become arranged in the equational plane of the cell and their kinetochores lie in the centre of the spindle.
Some of the spindle fibres are connected with the centromere of the chromosomes.
Anaphase- the beginning of Anaphase is marked by doubling of the centromeres. Now the sister chromatids of the chromosomes begin to move apart towards opposite poles of the spindle. During anaphasic movement of the chromatid the interzonal fibres between two centromeres lengthens and the chromosomal fibrils contract and finally disappear.
Telophase- reappearance of nucleolus. Spindle fibres disappear and nuclear membrane appear around the two opposite chromosomal sets. The chromosomes loses its identity turns into chromatin again. The Telophase ends when the two daughter nuclei are completely organised from the two sets of the daughter chromosomes.
Cytokinesis- the division of cytoplasm is known as cytokinesis. It is accomplished either through the formation of a cell plate between two nearly formed daughter nuclei or by means of peripheral furrowing.