Q. 23.7( 3 Votes )
•The division of nucleus is called Karyokinesis.
•It has four stages – Prophase, Metaphase, Anaphase and Telophase.
•It is the longest phase. Here thin, thread, network like chromatin reticulum condenses to form thick, short, coiled chromosomes.
•Each chromosome has two chromatids which are held at centromere.
•In animal cell centrosome splits into two. The centrioles present in centrosome have already duplicated and they start moving towards the opposite poles.
•Each centriole is surrounded by radiating rays called aster.
•Between two centrioles a number of fibres called spindle fibres appears.
•Nuclear membrane and nucleolus starts disappearing.
•The duplicated chromosomes have already reached and arranged on the equatorial plane of the cell.
•Each chromosome is attached by spindle fibre with its centromere.
•The centromere which is attached to the two chromatids divides and two sister chromatids separate from each other and start moving towards opposite poles.
•The movement of chromatids to opposite poles occurs due to contraction of spindle fibres.
•Daughter chromosomes reach the opposite poles.
•They again become thin, long network like chromatin reticulum.
•Nucleolus and nuclear membrane reappears.
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