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Cell Division - Mitosis & Meiosis
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CELL DIVISION: Mitosis & Meiosis
Can be divided into 2 stages: INTERPHASE.
Mnemonic:“Go Sally Go! Make Children!”
It is an equational division. Occurs in somatic cells.
Prophase, Metaphase, Anaphase, Telophase
Mnemonic: “People Meet And Talk”
Coiling of chromatin occurs, forming thin long threads.
By the end, chromosomes start forming,
Nucleolus & nuclear membrane starts disappearing by the end.
Spindle fiber formation starts.
Centriole in animal cells starts moving towards the poles.
Nuclear membrane and nucleolus has disappeared,
Spindle fibers have formed,
2 types of spindle fibers occur chromosomal fibers that are attached to chromosomes at the centromere & continuous fibers that join the 2 poles.
Chromosomes having two chromatids are seen,
Chromosomes align themselves on the equatorial plate due to contraction of spindle fibers.
Amphiastral mitosis occurs in animal cells & anastral mitosis occurs in plant cells.
Chromosomes start moving towards poles due to contraction of spindle fibers.
Various shapes of chromosomes are seen.
Chromosomes have reached the poles,
Uncoiling of chromosomes occur,
Nucleolus and nuclear membrane reappear,
Spindle fibers disappear.
2 nuclei are formed by the end.
Starts in mid-Anaphase and ends by the end of Telophase dividing the cell into 2 daughter cells.
Occurs by invagination of the cell membrane in animal cells & by cell plate method in plant cells.
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Meiosis I – reductional division:
Prophase I, Metaphase I, Anaphase I, Telophase I.
Prophase I: divided into 5 substages.
Mnemonic: Little Zara in Pink Dress is Dancing.
Chromatin coils forming thin long threads.
Further coiling of chromatin occurs.
Pairing of homologous chromosomes occurs due to the mutual attraction between them.
Synapsis is pairing of homologous chromosomes.
Synaptinemal complex occurs between homologous chromosomes, that helps in precise pairing.
Each chromosome splits longitudinally to form two chromatids attached at the centromere.
Bivalent changes into tetrad.
Crossing over, i.e., exchange of segments between non-sister chromatids occurs.
Crossing over occurs by the help of recombinase enzyme.
Homologous chromosomes try to separate.
Chromosomes remain attached at regions where crossing over has occurred.
Chaisma is the regions where crossing over has occurred.
Chromosomes pull themselves apart from the centromere, as a result chaisma starts moving towards ends.
This is Terminalization, which starts in diplotene stage.
Terminalization completes forming ring-shaped chromosomes.
Nucleolus & nuclear membrane starts disappearing, spindle fiber formation starts.
Nucleolus & nuclear membrane has disappeared, spindle fiber formation is completed.
Chromosomes align on equatorial plate.
Homologous chromosomes separate due to contraction of spindle fibers,
Terminal chaisma opens up & the chromosomes start moving towards poles.
Chromosomes reach poles and uncoiling starts.
Nucleolus & nuclear membrane reappear, spindle fibers disappear.
Two nuclei one at each pole are formed.
Meiosis II – equational division:
Prophase II, Metaphase II, Anaphase II, Telophase II.
Meiosis II is same as Mitosis.
4 daughters cells each having haploid number of chromosomes are produced.
Also watch:Cell Cycle, Chromosomes.
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