Shortcut Methods

Points to remember:

The sequence of events by which a cell duplicates its genome, synthesises the other constituents of the cell and eventually divides into two daughter cells is termed cell cycle.

The cell cycle is under genetic control.

The cell cycle is divided into two phase: interphase and Mitotic (M) phase.

The interphase lasts more than 95% of the duration of the cell cycle.

The M Phase represents the phase when the actual cell division or mitosis occurs.

Interpahse is further divided into G1 (Gap 1), S (Synthetic) and G2 (Gap 2) phase.

Sometimes the cells, such as heart cells and cells that divide occasionally, exit the G1 phase and enter the G0 phase (quiescent phase). Cells in this stage remain metabolically active and start dividing as per the requirement of the organism.

The amount of DNA per cell doubles during the S phase.

Mitosis is responsible for the cell growth and genetic continuity of the organisms.

The M Phase starts with the nuclear division (karyokinesis) and usually ends with division of cytoplasm (cytokinesis). Karyokinesis is subdivided into: Prophase Metaphase Anaphase and Telophase.

Mitosis is also known as equational division because the chromosome number in the parent and daughter cells remains the same.

Mitosis occurs primarily in vegetative (2n) cells of animals and plants.

Mitosis also occurs in haploid cells of certain lower plants and male drones of honey bees that are haploid.

Asexual reproduction or vegetative propagation occurs due to mitosis.

During mitotic prophase, condensation of chromosomes takes place and each chromosome has two chromatids.

During metaphase the two sister chromatids, which are held together by the centromere, are placed at the equator, referred to as metaphase plate.

Anaphase is characterised by centromeres splitting, chromatid separation and movement of chromatids to opposite poles.

During telophase the chromosomes cluster at opposite poles and decondense thus losing their individuality.

Cytokinesis in the plant cell occurs by cell plate formation whereas in animal cells it occurs by furrowing of the cytoplasm.



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