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cell division, cell cycle and structure of chromosomes. and gentics, first…

- - - - one vertical half of a duplicated chromosome is called a chromatid.
      - the point of attached of the two sister chromatids is called centromere .
        
        functions of centromere
        
        the centromere serves to attach the chromosomes with spindle fiber during cell division.
        
        it helps the sister chromatids to detach from each other during anaphase .
- - - - Histones
    - - DNA
        
        the DNA molecule is very large and hence it is described as macromolecule.
        
        it contains genetic information, aka Genes
      - RNA
- - - - for replacement
- - - - cell division-
        
        Mitosis
        
        production of diploid cells for growth and development .
        
        -it occurs in the sexually reproducing organism
        
        -there is a fusion of gametes
        
        if the chromosome number in the gamete is not reduced to half then when they fuse the chromosome number changes
        
        to keep the chromosome number constant gametes go under meiosis
        
        phases of mitosis
        
        Cytokinesis
        
        Animal cell– division by the appearance of the cleavage furrow which extends from the periphery to the middle ,,the cell membrane moves towards the middle and separates the two daughter cells.
        
        Plant cell- occurs because of the formation of cell plate(cellulose) which extends from the middle to the periphery separating the two daughter cells.
        
        Karyokinesis
        
        4 phases:
        
        Metaphase
        
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        Anaphase
        
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        Prophase
        
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        Telophase
        
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        Meiosis
        
        production of haploid cells or gametes.
        
        it occurs in the sexually reproducing organism
        
        there is a fusion of gametes
        
        if the chromosome number in the gamete is not reduced to half then when they fuse the chromosome number changes
        
        to keep the chromosome number constant gametes go under meiosis
        
        significance of meiosis
        
        1) chromosome no is reduced to half in gametes so after the fusion the chromosome no remains same.
        
        2) it provides for mixing up of genes
        
        the maternal and paternal gets mixed up during the first division as they separate from the homologus pairs.
        
        chiasma and crossing over
        
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    - - has three phases
        
        Synthesis phase (S)
        
        More DNA is synthesize and chromosomes are duplicated.
      - read the information of new DNA. pg no 13
  - - - formation of asteral fibers and the entire formation of the centrioles and the astral fibers is called astra formation.
- - - - Asexual reproduction , eg- amoeba or yeast cell.
        
        Maintains same chromosome number in daughter cells.