In 1880, first time dividing cell nucleus passes from a series of change is mitosis. Walther Fleming was German biologist who observe mitosis. Mitosis is kind of cell division which a cell is divide into two daughter cells with equal number. Eukaryotic is only cell which occur mitosis.
Stages of mitosis
The process of division of cytoplasm is cytokinesis. The process of division of nucleus is known karyokinesis. There are two major phases first of all discuss karyokinesis consist of four stages are as follow:
- Pro-phase
- Meta-phase
- Ana-phase
- Telophase
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| mitosis |
Pro phase
Genetic materiel found in nucleus is in loose thread form is chromatin. Chromosomes are highly order structure. Chromosome is made of two sisters chromatids who collect in centrometer.
During DNA, genetic material loose pack as chromatin. For mitosis DNA need more secure and tightly pack for easily division.
Mitotic are structures become from microtules that aid in arrangement. Every cell in Mitosis consist of two centrosomes. Centrosomes began to move on opposite site during this phase.
In plants cells, nucleus migrate center of cell prophase. Some of these not called mitosis such a Prokaryotes because does not have proper spindles and nucleus.
Meta-Phase
In meta phase, chromosomes become meta-phase plate they align them in theoretical line. Centrosomes describe to opposite end of cell. In this stages, cell completely check all chromosomes with detail who aligned with meta-phase plate. If the cell halting then error show in alignment or in spindle attachment.
Metaphase plate is a process of arrange the chromosomes in equator of cell forming. Fibers from kinetochore from opposite attached each with chromosomes. Mostly other fibers from opposite attach with each other.
Ana-phase
In ana-phase, sister pull to opposite exit of the cell. Spindle break the chromatids and not attached to chromatids. In the end of this stage, cells are success in separating copies into two opposite poles groups.
Telophase
In this phase, cell has elongated. The reversal of prophase is telophase. Telo-scope cell division take more steps but nuclear division easily.
Meiosis
Meioun means make smaller, meiosis comes from Greek word meioun. In 1876, meiosis was first time discover. Oscar Her twig was German biologist who first time discover meiosis. Inter-phase is divide into three equal parts S phase, G2 and G1. These interface follow by meiosis 1 and meiosis 11.
Meiosis I
Cytokineses and Karyokinesis are two main steps where meiosis I occur. Meiosis is further subdivided into telophase I, anaphase I, metaphase I and prophase I.
In prophase I, chromosomes combine with each other and make pairs is called synapsis. It is the longest phase in meiosis. each pair is called bivalent. Each bivalent has four chromatids called tetrad.
In 1911, Thomas Morgan was American geneticist who first time observed phenomenon crossing over in fruit fly.
Meta-phase I, pairs align with equal parts and make meta-phase plate.
In anaphase I, chromosome pull from one pole to each other pole and in last in telophase chromosomes arrive at the point pole. Each pole still divide into two chromatids and each half number pole.
Meiosis II
Meiosis II same like a mitosis. It is subdivide into prophase II, metaphase II, anaphase II and telophase II. Pro-phase I take more time compare to prophase II.
In meta-phase II, chromosomes attach with spindle fibers. Anaphase II, sister chromatids are pull. In last Telophase II, cell wall formation produce four daughter cells.
Due to binary fission meiosis does no occur in prokaryotes. In 1890, first time reproduction of meiosis discover by August Weizmann. He was German biologist. Disjunction and non-disjunction are two famous error occur in meiosis.
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